VTechWorks Repository :: Browsing by Author "Lee, John C."

Browsing by Author "Lee, John C."

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Altered Autonomic Nervous System Function in Chickens Divergently Selected for Body Weight
Kuo, Alice Yi-Wen (Virginia Tech, 2000-08-04)
Autonomic nervous system activity is related to body weight regulation. Based on the MONA LISA hypothesis it has been suggested that most obese subjects and animals have low sympathetic nervous system activity. The aim of this study was to investigate whether there are differences in autonomic nervous system activity between lines of chickens selected for either high (HWS) or low body weight (LWS). In Exp. 1, various pharmacological agents were injected intravenously, and the changes in blood pressure (BP) and heart rate (HR) of both HWS and LWS chickens were compared. The results showed that the HWS birds had a greater increase in BP and HR than the LWS following injection of atropine, a muscarinic receptor blocker, and LWS birds had a greater decrease in BP and HR to propranolol, a beta- adrenergic receptor blocker than the HWS birds. These results suggested that HWS chickens have higher parasympathetic tone, whereas LWS chickens have a higher sympathetic nervous system tone regulating the cardiovascular system. HWS and LWS chickens displayed a similar response in BP and HR following injection of the ganglion blocker tetraethylammonium chloride. These results suggest that there is no significant difference in the central autonomic nervous system in the cardiovascular regulation between HWS and LWS together. Since there does not appear to be any differences in the activity of the autonomic nervous system activity at the level of the central nervous system, these findings imply that the difference in response to atropine and propranolol could be caused by differences in adrenal activity. The ratio of heart rate and blood pressure after the injection of phenylephrine showed significant difference between these two lines of birds, but not when phenylephrine was injected following atropine. This result indicated that HWS are more dependent on the parasympathetic nervous system to regulate the baroreceptor reflex. The percentage of adrenal and sympathetic impact on the regulation of heart rate showed that LWS females required greater adrenal activity than the other birds. In Exp. 2, the body weight and food intake responses of HWS and LWS chickens to ip injections of reserpine were compared. Reserpine caused a transitory decrease in food intake and body weight in both lines of birds. However HWS chickens recovered more slowly from the depression caused by reserpine than the LWS chickens. This could be due to lower sympathetic nervous system activity. In conclusion, it appears that HWS may have lower sympathetic activity than LWS. Combining the results of both experiments, it appears that the HWS birds have lower sympathetic and higher parasympathetic activity. Furthermore central nervous system autonomic activity in BP and HR regulation is not different between HWS and LWS, but the activity of the adrenal gland may be different between these two lines of birds.
Apoptosis as a Mechanism of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-Induced Immunotoxicity
Kamath, Arati B. (Virginia Tech, 1998-11-10)
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly toxic environmental pollutant and is well known for its immunotoxic effects, particularly on the thymus. The exact mechanism by which TCDD induces thymic atrophy is not known. In the current study, we investigated whether TCDD triggers apoptosis in the thymocytes and whether Fas and Fas ligand play a role in TCDD-mediated immunotoxicity. Administration of a single dose of TCDD at 0.1, 1, 5 or 50 mg/kg body weight intraperitoneally into C57BL/6 +/+ mice caused a significant dose-dependent decrease in the thymic cellularity; whereas, in the C57BL/6 lpr/lpr (lpr) (Fas-deficient) and C57BL/6 gld/gld (gld) (Fas ligand-defective) mice, TCDD failed to induce a decrease in thymic cellularity at doses of 0.1-5 mg/kg body weight. In the lpr and gld mice, thymic atrophy was seen only at 50 mg/kg body weight of TCDD. Significant apoptosis was detected within 8-12 hours after injection in the wild type mice, whereas, in the lpr and gld mice apoptosis could not be detected. Upon culturing the thymocytes from TCDD-treated mice for 24 hours in vitro, the wild-type cells showed increased apoptosis when compared to the control; whereas, similar cells from lpr and gld mice did not show apoptosis. Furthermore, TCDD-treatment caused significant alterations in the expression of surface molecules on the thymocytes in the wild-type mice and minimal changes in the lpr or gld mice. Sera from TCDD-treated wild-type mice also exhibited increased levels of soluble Fas ligand. Also, TCDD-induced apoptosis was inhibited both in vitro and in vivo by caspase inhibitors and other inhibitors of apoptosis. Together, the current study demonstrates that TCDD-induced apoptosis plays an important role in thymic atrophy caused by TCDD in vivo. Furthermore, phenotypic changes in the density of thymocyte surface molecules may serve as a useful biomarker for chemical toxicity involving apoptosis. The current study also demonstrates that Fas-Fas ligand interactions play an important role in the induction of apoptosis and immunotoxicity by TCDD.
Application and Evaluation of Unified Medical Language System Resources to Facilitate Patient Information Acquisition through Enhanced Vocabulary Coverage
Mills, Eric M. III (Virginia Tech, 1998-04-13)
Two broad themes of this research are, 1) to develop a generalized framework for studying the process of patient information acquisition and 2) to develop and evaluate automated techniques for identifying domain-specific vocabulary terms contained in, or missing from, a standardized controlled medical vocabulary with emphasis on those terms necessary for representing the canine physical examination. A generalized framework for studying the process of patient information acquisition is addressed by the Patient Information Acquisition Model (PIAM). PIAM illustrates the decision-to-perception chain which links a clinician's decision to collect information, either personally or through another, with the perception of the resulting information. PIAM serves as a framework for a systematic approach to identifying causes of missing or inaccurate information. The vocabulary studies in this research were conducted using free-text with two objectives in mind, 1) develop and evaluate automated techniques for identifying canine physical examination terms contained in the Systematized Nomenclature of Medicine and Veterinary Medicine (SNOMED), version 3.3 and 2) develop and evaluate automated techniques for identifying canine physical examination terms not documented in the 1997 release of the Unified Medical Language System (UMLS). Two lexical matching techniques for identifying SNOMED concepts contained in free-text were evaluated, 1) lexical matching using SNOMED version 3.3 terms alone and 2) Metathesaurus-enhanced lexical matching. Metathesaurus-enhanced lexical matching utilized non-SNOMED terms from the source vocabularies of the Metathesaurus of the Unified Medical Language System to identify SNOMED concepts in free-text using links among synonymous terms contained in the Metathesaurus. Explicit synonym disagreement between the Metathesaurus and its source vocabularies was identified during the Metathesaurus-enhanced lexical matching studies. Explicit synonym disagreement occurs, 1) when terms within a single concept group in a source vocabulary are mapped to multiple Metathesaurus concepts, and 2) when terms from multiple concept groups in a source vocabulary are mapped to a single Metathesaurus concept. Five causes of explicit synonym disagreement between a source vocabulary and the Metathesaurus were identified in this research, 1) errors within a source vocabulary, 2) errors within the Metathesaurus, 3) errors in mapping between the Metathesaurus and a source vocabulary, 4) systematic differences in vocabulary management between the Metathesaurus and a source vocabulary, and 5) differences regarding synonymy among domain experts, based on perspective or context. Three approaches to reconciling differences among domain experts are proposed. First, document which terms are involved. Second, provide a mechanism for selecting either vocabulary-based or Metathesaurus-based synonymy. Third, assign a "basis of synonymy" attribute to each set of synonymous terms in order to identify the perspective or context of synonymy explicitly. The second objective, identifying canine physical examination terms not documented in the 1997 release of the UMLS was accomplished using lexical matching, domain-specific free-text, the Metathesaurus and the SPECIALIST Lexicon. Terms contained in the Metathesaurus and SPECIALIST Lexicon were removed from free-text and the remaining character strings were presented to domain experts along with the original sections of text for manual review.
Atrial natriuretic peptide and streptozotocin-induced diabetes in rats
Black, Leslie Seale (Virginia Tech, 1991-04-17)
This study was undertaken to determine whether immunoreactive atrial natriuretic peptide (irANP) concentrations in plasma and atrial tissue are altered in experimental diabetes mellitus (DM), and to compare the response of the DM and normal groups to exogenous administration of ANP. OM was induced by intraperitoneal injection of 45 mg/kg streptozotocin in male Sprague-Dawley rats. After three weeks of established OM (glucosuria and blood glucose> 250 mg/dl), plasma irANP levels were 149.6 ± 19.4 pg/ml in the OM group (n = 18) and 86.3 + 12.9 pg/ml in the normal group en = 12, P <0.01). Atrial tissue irANP levels were significantly lower in the OM group (38.1 ± 7.8 ng/mg, n = 7) than in the normal group (60.1 ± 1.3 ng/mg, n = 4, P < 0.02). In response to intravenous infusion of ANP (2.5 ug/kg prime, followed by 0.1 ug/kg/min for 30 minutes), urine flow rate and urine sodium and potassium excretion rates increased significantly in the normal group (n = 6, P < 0.05), while no significant responses were found in the OM group (n = 6). It is concluded that plasma levels of ANP are significantly elevated in streptozotocin-induced diabetes in rats, and that atrial tissue stores are significantly depleted in this diabetic model. In addition, the renal response to exogenously administered ANP appears to be diminished in streptozotocin-induced OM.
Body composition of dogs determined by carcass composition analysis, deuterium oxide dilution, subjective and objective morphometry, and bioelectrical impedance
Burkholder, William Joseph (Virginia Tech, 1994-05-16)
Prediction of body composition was assessed in thirty-eight female and thirty-seven male random source dogs using in vivo methods of deuterium oxide dilution, subjective and objective morphometry, bioelectrical impedance and ultrasound, either separately or in various combinations. Carcass composition determined by chemical analyses of carcass homogenates served as criterion measures of body composition. Dogs were selected based on gender, body weight and body condition score. Body weight ranged from 7.3 to 34.5 kilograms (kg), subdivided into 4.5 kg increments with 6 female and 6 male dogs per increment. Body condition was categorized as thin, optimum or obese using a defined criteria, body condition scoring system (subjective morphometry) with 12 female and 12 male dogs per body condition category. Selection criteria produced 18 body weight condition groups with 2 female and 2 male dogs per group. One additional male and 2 female dogs were included for economic and ethical reasons. Equations to predict carcass composition from in vivo measurements were derived using standard regression techniques. Influence diagnostics, residual analysis and data splitting were used to validate predictive equations. Predictions from deuterium oxide dilution produced the most precise estimates of body composition. Average standard errors of estimation (SEE) from deuterium equations were 1.3, 1.8, 1.0, and 0.4 percent for percentages of body moisture, fat, protein and ash, respectively, and 0.39, 0.57,0.21 and 0.08 kg for absolute quantities of moisture, fat, protein and ash, respectively. Morphometry produced the most imprecise, but economical, estimates. Average SEE from morphometry equations for proportions were 3.0, 4.0, 1.3, and 0.4 percent, and 0.9, 0.9, 0.3 and 0.07 kg for absolute quantities of moisture, fat, protein and ash, respectively. Subjective morphometry could estimate body fat with an average SEE of 3.4 percent and correctly categorized 75 percent of the dogs. Bioelectrical impedance and ultrasound produced predictions with average SEE intermediate to deuterium and morphometry. Bioelectrical impedance was equivalent to deuterium dilution on the basis of cost per unit improvement in SEE, but ultrasound was not cost effective.
Comparative thyroid function in developing and adult precocial Japanese quail and altricial Ring doves
McNichols, Michael John (Virginia Polytechnic Institute and State University, 1987)
I compared Japanese quail Coturnix japonica, and Ring doves Streptopelia risoria, in the development of thyrotropin (TSH) influence on thyroid hormone (TH) content in the thyroid gland (TG) and the serum, and on TG-cAMP content. In embryos, pituitary gland (PG)-TSH content was measured by an avian bioassay system. Adult quail and doves were studied for comparability of thyroid gland function when receiving comparable dietary iodine. Also, thyroid function in adult doves was compared with different iodine intake. In embryonic quail, there is considerable maturation of thyroid function prior to hatching, TG-TH content is low but detectable in day 8 embryos; TG-TH content increases 300X between day 8 and hatching (16.5 day incubation). Pituitary TSH was detectable on embryonic day 8, with higher levels found closer to hatching. The TG of 8 day embryos responds to TSH injection by increased TG-cAMP content but the serum TH response to TSH does not mature until day 9. Serum TH concentrations suggest that the TG is under the control of endogenous TSH from the pituitary during the latter part of incubation. In doves, most of the development of thyroid function and the maturation of its pituitary control occur after hatching, Thus, thyroid functional development is much later in doves than in quail. TG-TH content is extremely low in embryos and nestlings up to 3 days after hatching, increases slowly innestlings up to day 10, then increases sharply. Serum TH are very low in embryos and rise steadily in nestlings to plateau after day 8. Pituitary TSH content is undetectable in embryos and in nestlings until day 4. The TG does not respond (based on serum TH concentrations) to TSH injection through the day of hatching (day 16; mean incubation period of 16.5 days), but an increase in serum TH occurs in day 2 nestlings in response to TSH injection. The magnitude of this response continues to increase during the first week after hatching. In adult birds, thyroid function was studied in Japanese quail and Ring doves, when both were fed the same dietary iodine (I; 930 μg I/kg). We also compared thyroid function in groups of doves receiving low I (< 100 μg I/kg) or moderate I (930 μg I/kg). We measured thyroid gland (TG) weight, TG stable I (¹²⁷I) I content, TG ¹²⁵I uptake, ¹²⁵I labeling of thyroid hormones, and serum ¹²⁵I thyroxine (T4) half-life. Triiodothyronine (T3) and thyroxine (T4) concentrations in TGs and serum also were determined. Our results indicate that doves and quail receiving the same dietary I show similar serum T3 concentrations and TG functional state, but that there are some differences between the species in the way which this equivalent functional state is achieved. Doves fed low dietary 1 (< 100 μg 1/kg) when compared to doves with moderate I intakes (930 μg I/kg) showed similar serum T3 concentrations despite reduced serum T4 concentrations and TG-hormone stores. This study demonstrates that quail and doves show similar TG function and a similar regulation of serum T3, the · presumed metabolically active hormone, when dietary I availability is the same. Also, doves with low dietary I show decreases in some measures of TG function compared to doves with moderate I, but still maintain a level of serum T3 comparable to that with adequate I intake. This set point regulation of T3 therefore appears to be independent of serum T4 or TG hormone stores.
Controlled cross circulation: effects on donor hemodynamics
Kuntz, Charles A. (Virginia Tech, 1994-05-12)
Controlled cross circulation was performed in six pairs of dogs to assess hemodynamic changes in the donor dog. Cardiopulmonary bypass was performed for 45 minutes, with an aortic cross clamp time of 3 5 minutes. Anesthesia was maintained in the donor dog with 1.8% end-tidal isoflurane. Parameters before and after controlled cross circulation were compared using a Wilcoxon Signed Rank Test. Donor left ventricular dP/dt max, pulmonary capillary wedge pressure, blood volume, systemic vascular resistance, heart rate, total protein, platelet count, and white blood cell count did not change significantly. Donor cardiac output, end diastolic volume, central venous pressure, stroke volume, mean arterial blood pressure, and packed cell volume all decreased significantly (p
Determination of cardiac output across a range of values in horses by M-mode echocardiography and thermodilution
Moore, Donna Preston (Virginia Tech, 2004-02-12)
Determinations of cardiac output (CO) by M-mode echocardio-graphy were compared with simultaneous determinations by thermodilution in 2 conscious and 5 anesthetized horses. A range of cardiac outputs was induced by use of a pharmacological protocol (dopamine, 4 ug/kg/min, dobutamine, 4 ug/kg/min, and 10 ug/kg detomidine plus 20 ug/kg butorphanol, in sequence). Changes from baseline CO in response to each drug were evaluated, and data was analyzed to determine whether there were any interactions between drug treatment and measurement method. The mathematical relationship between CO as determined by M-mode echocardio-graphy (COecho) and as determined by thermodilution (COTD) was described and used to predict COTD from COecho. The 2 methods were compared with respect to bias and variability in order to determine the suitability of COecho as a substitute for COTD . Sources of the variability for each method were determined. Determination of CO by either method in standing horses was prohibitively difficult due to patient movement. The pharmacologi-cal protocol was satisfactory for inducing a range of cardiac outputs for the purpose of method comparison; however, use of dopamine did not offer any additional benefit over the use of dobutamine and was generally less reliable for increasing CO. Inclusion of detomidine provided an additional change in CO but did not increase the overall range of CO over that produced by halothane and dobutamine. COecho and COTD were significantly related by the predictive equation COTD = (0.63 +/- 0.157) x COecho + (16.6 +/- 3.22). The relatively large standard errors associated with COecho measurements resulted in a broad 95% prediction interval such that COecho would have to change by more than 100% in order to be 95% confident that the determined value represents true hemodynamic change. COecho underestimated COTD by a mean of 10 +/- 6.3 l/min/450 kg. The large standard deviation of the bias resulted in broad limits of agreement (-22.3 to +2.3 l/min/450 kg). Measurement-to-measurement variability accounted for 28% of the total variation in COTD values and 64% of the total variation in COecho values. Results might be improved if the mean of 3-5 consecutive beats was used for each measurement, but as determined in this experiment, COecho is too variable to have confidence in its use for precise determinations of CO.
The effects of atrial repolarization on exercise-induced ST-segment depression in apparently healthy females
Brown, Rhonda K. (Virginia Tech, 1994-03-17)
The relationship between the PQ-segment slope on ST-segment depression during vigorous exercise was examined in 26 apparently healthy females between 18 and 26 years of age. Each subject performed 2 submaximal cycle ergometer exercise tolerance tests (trial A and trial B) on nonconsecutive days wherein the following variables, as delta scores, were measured; P-wave amplitude (microvolts), PQ-segment slope (uV!sec), and J-point at 0 and 60 msec (uV). Each variable was measured by both visual and computer averaging. The degree of reproducibility within and between trials differed for the visual and computer averaged measures. Generally higher reproducibility was found with computer averaging particularly within trial B (r =0.63-0.89, p50 uV) at both 0 and 60 msec after the J-point in lead II. However, there was a greater percentage (91%) of flat PQ-segment slopes with clinically significant ST-segment depression at J-point 0 msec in lead V5. These findings suggest possible influence of lead selection on the measurements of the PQ-segment slope and ST-segment. Implication of clinical application would be to use lead VS for diagnosing CHD and by measuring ST-segment depression at J-point 60 msec. However when screening exercise ECG tests in apparently healthy women use J-point at 0 msec.
Effects of Low and High Sodium Chloride Diets and Furosemide Administration on Cardiac Function, Plasma Electrolyte Concentrations, and the Renin-Angiotensin-Aldosterone System
Swancott, Cindy Marie (Virginia Tech, 1998-04-14)
Congestive heart failure is commonly treated with a low sodium diet and diuretic. The purpose of this treatment is the reduction of preload, or blood volume presented to the diseased cardiac muscle. The purpose of this study was to assess the roles of dietary sodium and furosemide on cardiac function, plasma electrolyte concentrations, and the renin-angiotensin-aldosterone system, in healthy canines. Twenty mixed-breed canines were allotted to one of four groups, Group I - Dogs fed low sodium diet (0.08% sodium), Group II - Dogs fed high sodium diet (1.0% sodium), Group III - Dogs fed low sodium (0.08%) and treated with furosemide (2 mg/kg orally (PO) every twelve hours (BID)), and Group IV - Dogs fed high sodium (1.0%) and furosemide ( 2 mg/kg PO BID). Cardiac function was assessed via echocardiography on days 0, 21,and 53. Plasma electrolyte concentrations were measured on days 0, 21, and 35. Activation of the renin-angiotensin-aldosterone system was evaluated on days 0, 21, 35, and 53. Low and high sodium diet with and without furosemide treatment did not alter cardiac function, plasma sodium, or plasma potassium concentrations. However, furosemide treatment combined with a low sodium diet resulted in the lowest plasma chloride concentrations, on days 21 and 35 (p<0.05). Furthermore, furosemide treatment resulted in significant alterations in the renin-angiotensin-aldosterone system, on days 21, 35, and 53, (p < 0.0001). Furosemide treatment significantly increased renin activity and aldosterone concentration. The interaction between furosemide and the low sodium diet yielded a greater increase in plasma renin activity and plasma aldosterone concentrations than furosemide administration with the high sodium diet. These results suggest direct activation of the renin-angiotensin-aldosterone system by furosemide. Future research is warranted in congestive heart failure subjects, due to the adverse affects of decreased plasma chloride concentrations and activation of the renin-angiotensin-aldosterone system.
Effects of opioid antagonism on thermoregulation during prolonged exercise in the heat
Hickey, Matthew Sean (Virginia Tech, 1990-08-05)
Five adult male volunteers were studied to investigate the effect of opiate receptor blockade on the physiological response to a maximum of 60 minutes of stationary cycling at 70% V02peak in a hot (33 0 C/65% RH) environment. Exercise bouts were conducted following the administration of naloxone (4mg IV) 5 minutes prior to exercise with a follow-up 4mg dose at 25 minutes of exercise. In the placebo trial, volume-matched doses of saline were administered at the same points. No significant drug effect was observed on rectal or mean skin temperature during exercise. Post-exercise skin temperature was significantly (P<.001) higher on naloxone versus saline. Forearm blood flow (FBF) was consistently higher from minute 25 of exercise until test termination, although only the minute 25 and minute 55 data points were significantly elevated (P<.05, P<.005, respectively) . The rectal temperature threshold at which FBF plateaued was higher on naloxone (P=.054), and the FBF: rectal temperature slope was higher on naloxone throughout the trial. No significant changes were observed in heart rate or estimated mean arterial pressures, although both were consistently lower on naloxone. Gross sweat response was not altered by the drug. Plasma Beta-Endorphin was significantly (P<.Ol) higher on naloxone versus saline, and Beta-Endorphin was significantly elevated in the naloxone trial only. The observation that FBF was significantly higher on naloxone without inducing compensatory heart rate or blood pressure changes suggests that the opioids may be involved in the blood volume shifts that occur during prolonged exercise in the heat.
Effects of organophosphate esters on blood vessels: a physiological, pharmacological, and histological assessment of involvement in organophosphorus-induced delayed neuropathy (OPIDN)
McCain, Wilfred C. (Virginia Tech, 1994)
The contribution of the cardiovascular system. to organophosphate-induced delayed neuropathy (OPIDN) was examined using in situ and in vitro models for demonstration of response to vasoactive agents (e.g., the cholinergic agonist, acetylcholine; the α1 agonist, phenylephrine; and the β2 agonist, salbutamol). These responses were compared before and 1, 3, 7, and 21 days after hens were administered cyclic phenyl saligenin phosphate (PSP, 2.5 mg/kg i.m.), an OP that induces OPIDN but does not significantly inhibit acetylcholinesterase activity, and paraoxon (PXN, 0.1 mg/kg i.m.), an OP that inhibits acetylcholinesterase activity but does not induce OPIDN. The capability of verapamil, a calcium channel blocker, to attenuate these responses was examined, as this agent ameliorates OPIDN. For the in situ study, the ischiadic artery was cannulated and alterations in pressure measured at a constant flow used to indicate changes in vascular resistance. Changes in vascular resistance in response to acetylcholine, phenylephrine, and salbutamol that were different from those in control and PXN-treated hens were noted 1 and 3 days after administration of PSP. These changes were attenuated in hens given PSP and verapamil. Vascular segments from the ischiadic artery were used to provide an in vitro model to determine if OPs caused direct vascular damage that was responsible for effects seen in the in situ model. In the in vitro model, however, responses of PSP and PXN were similar and not modified in vascular segments from hens given verapamil as well as the OPs. This indicated that the contribution of the cardiovascular system to OPIDN was due to more than a direct effect on relatively large caliber vessels. The contribution of the cardiovascular system to OPIDN also did not appear to relate to morphological changes induced by administration of OPs, as no changes in vascular morphology were noted. An OP-induced effect that could contribute to vascular effects noted are levels of plasma catecholamines. These levels were altered in hens given PSP or PXN, with increases seen after administration of PSP and decreases seen after administration of PXN. These alterations in plasma catecholamine levels were attenuated in hens given both verapamil and OP.
Effects of ovokinin on isolated aortas of guinea pigs, normotensive and spontaneously hypertensive rats
Yim, Cynthia (Virginia Tech, 1998-06-25)
Ovokinin, a peptide recently isolated from an enzymatic digest of ovalbumin, has been shown to mediate vasorelaxation of the canine mesenteric artery through bradykinin B1 receptors. Bradykinin can mediate both vasorelaxation and vasocontraction depending upon the tissue or species investigated. The aim of this study was to characterize ovokinin further by determining whether the effects of this peptide, like bradykinin, vary when using different species and tissue preparations as well as different contracting agents. Isolated aortic rings from guinea pigs, normotensive rats, and spontaneously hypertensive rats were exposed to phenylephrine, prostaglandin F2a, potassium chloride, or bradykinin. Bradykinin contracted guinea pig and spontaneously hypertensive rat aortas, however, it had no effect on normotensive rat aortas. In this study, ovokinin did not exhibit activity in any of the preparations except in guinea pigs, where it potentiated the contraction elicited by bradykinin only. This potentiation was blocked when rings were pretreated with captopril, a kininase II inhibitor. Ovokinin may also exhibit slight vasorelaxing activity in spontaneously hypertensive rat aortas precontracted with prostaglandin F2a. These findings suggest that, like bradykinin, the effects of ovokinin are species- and tissue-dependent. The action of ovokinin on the guinea pig aorta may involve kininase II, which is partly responsible for the degradation of bradykinin and other kinins.
Effects of the Angiotensin II Antagonist, Losartan, on Circulo-Respiratory Responses to Submaximal Exercise in Hypertensive Women
Craft, Laura Lee III (Virginia Tech, 1997-10-30)
The effects of the antihypertensive agent Losartan (Lo), on acute exercise performance was assessed in six sedentary, hypertensive women. The purpose, benefits and potential risks of the study were explained to each subject and their informed consent received. In a double blinded crossover design subjects were randomized to 7 days of (Lo) 50 mg, once every morning or placebo (Pl). Subjects reported to the laboratory for an exercise trial on the 7th treatment day. They received the final treatment dose 2.5 hours before the exercise trial. Blood samples for analysis of plasma renin activity (PRA) and Angiotensin II (Ang II) were obtained 15 min before the exercise trial began. In each trial, the subject rested for 15 min in a seated position on the stationary cycle. Hemodynamic and respiratory measurements were obtained. They began exercise at a workload equivalent to 45% VO2 pk for 15 min, immediately followed by a progression of 30 Watt*2 min-1 until volitional fatigue. Measurements included: blood pressure, heart rate, respiratory gas exchange, cardiac output (Q) and rate of perceived exertion (RPE). Total peripheral resistance index (TPRI), stroke volume index (SVI) and rate pressure product (RPP) were calculated. Compared to the pre-administration conditions, 1 week of Losartan treatment significantly reduced (p< .05) resting MAP, SBP and DBP in these subjects. Losartan treatment did not modify submaximal exercise HR, Q, VO2 or RPE. The RPP also was not different between the Lo and Pl trials at rest (p >.05), but was reduced at peak exercise with Lo treatment (p<.05). Losartan significantly reduced calculated TPRI at rest (p< .05) in comparison with Pl (12%) but not during steady-state exercise. Circulating plasma levels of Ang II and PRA were significantly higher with Lo (p<.05). In conclusion, Losartan, a new antihypertensive medication, reduced BP without altering exercise performance in hypertensive women. Losartan is an appropriate first line antihypertensive agent to use in treatment of hypertensive individuals who wish to participate in a regular exercise program.
Genomic and Physiological Differences for Ghrelin and Leptin Receptor in Lines of Chickens Selected for High and Low Body Weight
Kuo, Alice Yi-Wen (Virginia Tech, 2003-12-08)
Autonomic nervous system (ANS) activity is related to body weight regulation. Based on the hypothesis that Most Obesities kNown Are Low In Sympathetic Activity (MONA LISA), it has been suggested that most obese subjects and animals have low sympathetic nervous system activity. Leptin, leptin receptor, and ghrelin genes influence the ANS regulation of body weight and food intake. The aim of this study was to investigate whether there are differences in leptin, the leptin receptor, or ghrelin regulation between lines of chickens selected for high (HWS) or low body weight (LWS). Intraperitoneal injections of reserpine were administrated to chickens from the HWS and LWS lines. Body weight and food intake were then compared to evaluate ANS regulation. While reserpine caused a transitory decrease in food intake and body weight in both lines, the magnitude of the change was greater in the HWS than in the LWS chickens. However, chickens from the LWS line exhibited greater catecholamine and indoleamine level changes in response to reserpine than those from the HWS line. Therefore, HWS chickens were more sensitive to the body weight-reducing effects of reserpine than LWS lines, while LWS chickens appeared to have greater sympathetic nervous system activity. Food and water intakes were differentially affected in HWS and LWS chickens in response to intracerebroventricular administration of human recombinant leptin. Leptin caused a linear decrease in food intake in the LWS line, but no effect on food intake in the HWS lines. The HWS chickens tended to have reduced water intake following leptin administration. These results suggest that the leptin receptor, or the down-stream neuropeptide regulation pathway mediating the effect of leptin; may be different between chickens from the HWS and LWS lines. Leptin, insulin like growth factor (IGF)-1, and IGF-2 concentrations in the plasma of HWS and LWS lines of chickens were evaluated. Leptin, IGF-1 and IGF-2 levels were significantly higher in the LWS than HWS chickens. The HWS female leptin concentrations were significantly lower than in HWS males or LWS females. Male chickens had greater IGF-1 concentrations in the plasma than female chickens. However, the concentration of IGF-2 did not differ between sexes. The difference in leptin concentrations in these lines and sexes may explain the differences in age of sexual maturity. Different IGF-1 and IGF-2 concentrations may be involved in the obese and anorexic conditions, fast and slow growth, and high and low food consumption found in these two lines of chickens. Differences in the gene sequence of the leptin receptor were observed in HWS and LWS lines of chickens. A single nucleotide polymorphism (SNP) in the intron between exon 8 and 9 introduced a restriction site for the enzyme Sel I in the HWS, but not the LWS line. Two SNP were detected in the leptin receptor cDNA region at nucleotides 189 and 234. At nucleotide 189, the LWS line has both a homozygous (T-T) and heterozygous (C-T), whereas the HWS line has only homozygous (T-T) form. The SNP found in nucleotide 234 introduces a restriction site Mse I in the HWS, but not the LWS line. These specific changes may be directly involved or closely linked to differences between the two lines in either the coding or regulatory domains of the leptin receptor. Differences in the leptin receptor gene expression between HWS and LWS lines of chickens in various organs and ages were observed. Leptin receptor expression in the whole brain was significantly different between sexes at 28 days-of-age in the HWS and LWS lines. The LWS line had higher leptin receptor gene expression in the liver at 2 days-of-age than at 56 and 363 days-of-age, but no differences were observed in the HWS line. In addition, at 2 days-of age, liver leptin receptor gene expression was higher in LWS than HWS chickens, but the reverse was observed at 363 days-of age. In adipose tissue, leptin receptor expression was higher in the LWS than HWS line. Leptin receptor expression in adipose tissue was greater at 363, than 28 and 56 days-of-ages. Our results showed that changes in the regulation of leptin and the leptin receptor were associated with sex, age, and growth. Differences in the ghrelin gene in the HWS and LWS lines under different feeding conditions were investigated. Both HWS and LWS chickens have six extra base pairs in the 5'-untranslated region. The LWS male ghrelin gene expression was significantly lower than in the LWS female and HWS male. The 84 day-old males had lower gene expression than 84 day-old females and 363 day-old males. When comparing different feeding methods, females allowed ad libitum feed consumption had a lower cycle threshold cycle number (CT) ratio than males allowed ad libitum feeding or fasted females. However, the inflection point cycle number of ad libitum fed females was lower than that of the ad libitum fed males, but greater than the fasted females. Ghrelin gene expression was different between the two lines of chickens, and the expression of ghrelin in chickens was influenced by body weight selection, sex, age, and feeding condition.
Lens calcium homeostasis and selenite cataract
Wang, Zaiqi (Virginia Tech, 1992)
A 3- to 5-fold increase in Ca2+ accompanies cataract formation induced by selenite. The mechanism of selenite cataractogenesis involves calcium activation of calpain with subsequent proteolysis within the lens nucleus. This study was undertaken to investigate the biochemical mechanisms that lead to calcium accumulation in these circumstances. The components responsible for rat lens calcium regulation were defined by using either lens membrane vesicle preparations or intact lenses. Both Na+ gradient-dependent Ca2+ uptake and efflux occurred in lens membrane vesicles. Experiments with intact lenses showed that Na + ICa2 + exchange plays an important role in lens calcium regulation. ATP-dependent Ca2+ uptake and Ca2+ -dependent ATP hydrolytic activity have been characterized in lens membrane vesicles. Therefore, both Ca2+ -ATPase and Na + ICa2+ exchange participate in rat lens calcium regulation. Calcium accumulation in lenses treated by selenite may result from either increased influx (via non-selective cation channel), decreased efflux (via Ca2 +-ATPase and Na+ ICa 2+ exchange) or both. The selenite effects on the different components involved in lens calcium regulation were tested.
Magamp post-regulator applied to a quasi-resonant converter and magamp operation under extreme load condition in a PWM converter
Lee, John C. (Virginia Tech, 1988-06-26)
Two issues pertinent to magamp post regulator are treated in this thesis. One of the issues considered is the operation of a magamp under extreme loading conditions. Practical design equations are derived to allow magamp operation under extreme load conditions such as shutdown of output, foldback of output current and very light load (discontinuous operation). The other issue considered concerns with magamp post regulation for a quasi-resonant converter. A magamp circuit is proposed, designed and tested for a zero current switching quasi-resonant forward converter. It demonstrates that output regulation in a quasi-resonant converter can be achieved with a fixed switching frequency operation. It also demonstrates the feasibility of multiple regulated output application of a quasi-resonant converter.
Molecular mechanisms of the carcinogen chromium(VI)-induced DNA-protein crosslinking in cultured intact human cells
Mattagajasingh, Subhendra N. (Virginia Tech, 1995)
Chromium(VI)-induced DNA-protein crosslinking is implicated in chromium Carcinogenicity. However, the mechanism of chromate-induced DNA-protein crosslinking has not been established. Based on the current literature and our preliminary data, we hypothesized that Cr(VI)-induced DNA-protein crosslinks may, in part, be due to generation of active oxygen species following the intracellular reduction of Cr(V1) and that antioxidants may ameliorate the genotoxic and carcinogenic effects of Cr(VI). We proposed to test our hypothesis with the following specific aims: 1) To characterize the DNA-protein complexes induced by the carcinogen Cr(VI) in MOLT4 cells, 2) To investigate the effect of Cr(VI) on "oxidative-stress status" of the cell, 3) To distinguish between proteins directly cross-linked by Cr(III) and those that are cross-linked oxidatively during intracellular Cr(VI) reduction, and 4) To identify major proteins that are complexed to DNA by Cr(III) or via oxidative mechanisms, in MOLT4 cells treated with chromate. Together, the proposed studies should provide new information regarding the mechanism of chromium genotoxicity and carcinogenicity. The identification of specific protein(s) involved in DNA-protein crosslinks may also provide an useful tool to develop biomarkers for assessment of chromium risk. The results of our studies indicate the following: (1) Characterization of chromate-induced DNA-protein complexes in MOLT4 cells: A selected group of non-histone proteins were found to crosslink to DNA upon chromate exposure. The subcellular localization of these proteins was found to be in the nuclear fraction, specifically in the nuclear matrix, suggesting the proximity of these proteins to DNA. Analysis of the stability of the crosslinks to disruptive chemicals and enzymes suggested that Cr(III) and sulfhydryl groups are partially involved in such complexes. However, resistance of some proteins to treatments such as EDTA, B-mercaptoethanol or thiourea, and their need for nuclease digestion to release them by fragmenting DNA indicated that those proteins may be covalently crosslinked to DNA via oxidative mechanisms. (2) Effect of Cr(VI) on the "oxidative-stress status" of MOLT4 cells: Chromate treatment of cells was found to not only decrease the level of low molecular weight antioxidants and antioxidant enzymes, but also induce the formation of active oxygen species, such as hydrogen peroxide. A mechanism for this hydrogen peroxide-inducing effect of chromate was proposed. A close correlation was observed between the cellular levels of oxidants and DNA-protein crosslinking following chromate exposure. Pretreatment of cells with antioxidants also illustrated correlative changes in chromate-induced DNA-protein crosslinking and the cellular level of oxidants. Intracellular generation of reactive species of chromium, such as Cr(V), and generation of active oxygen species during the reaction of Cr(VI) and its reduced forms such as Cr(V) and Cr(III), with its biological reductants were studied by EPR spectrometric techniques. Furthermore, exposure of cells to chromate was also found to induce protein oxidation and lipid peroxidation that were effectively suppressed by antioxidant pretreatment of cells, suggesting a role of reactive oxygen species, protein carbonyls and malonaldehyde in inducing DNA-protein crosslinking. (3) Detection of proteins crosslinked to DNA by direct participation of Cr(III) and via oxidative mechanisms upon chromate exposure of cells: Chromate-induced DNA-protein complexes that were formed by direct participation of Cr(III) were distinguished from those that were formed via oxidative mechanisms by using EDTA to specifically dissociate Cr(III) mediated crosslinks, and α-tocopherol succinate to suppress oxidatively crosslinked proteins, respectively. DNA-protein complexes induced by x-ray irradiation of cells and incubation of isolated nuclei with Cr(III) were used as positive controls for crosslinking of proteins to DNA by oxidative mechanisms and by Cr(III), respectively. A common group of identical non-histone proteins were found to complexed to DNA by Cr(VI), Cr(III), and x-ray, however a 51 kD basic protein appeared to be predominantly crosslinked to DNA by participation of Cr(III), while a 49 kD acidic protein appeared to be primarily crosslinked by oxidative mechanisms. Chromate-induced DNA-protein crosslinks isolated from α-tocopherol pretreated cells exhibited an increase in the fractionation of DNA by restriction enzymes as compared to that isolated from cells treated with chromate alone, further supporting the involvement of oxidative mechanisms in the process. Formaldehyde, on the other hand, primarily crosslinked histones to DNA, indicating that specificity in protein-DNA crosslinking is dependent on the chemical nature of the crosslinking agent. (4) Identification of major proteins complexed to DNA upon chromate treatment: Attempts were made to identify the proteins that crosslink to DNA upon chromate exposure of cells by using antibodies to candidate proteins, and N-terminal sequencing followed by searching for their homology in GeneBanks. Actin, lectin, and aminoglycoside nucleotidyltransferase were identified as participants in chromate-induced DNA-protein crosslinking. (5) DNA protein complexes as a biomarker of exposure to chromate: Finally, DNA-protein crosslinks were detected immunologically by developing an antiserum to chromate-induced DNA protein crosslinks. The antiserum predominantly reacted with nuclear proteins, and DNA-protein crosslinks induced by Cr(VI), Cr(III) and x-ray, but reacted poorly with formaldehyde-induced DNA-protein crosslinks, further suggesting specificity in DNA-protein crosslinks induced by different crosslinking agents. The antiserum did not react with DNA-protein crosslinks isolated from control cells. Taken together, we conclude that DNA-protein crosslinks are caused by intracellularly generated Cr(III) as well as active oxygen species formed following exposure to Cr(VI). Hence, it appears that antioxidants may be useful in reducing the genotoxic and carcinogenic effect of chromium(VI) in human populations exposed to this toxicant. Participation of the three nuclear proteins, actin, lectin, and aminoglycoside nucleotidyltransferase, in chromate-induced DNA-protein crosslinks suggest that these proteins may be parts of chromatin structure. Since these proteins are crosslinked to DNA by chromate, they may be used as biomarkers of chromate exposure.
Purification and characterization of a protein phosphatase (PP1-Arch) from the archaebacterium Sulfolobus solfataricus, isolation and expression of its gene
Leng, Jie (Virginia Tech, 1994-11-05)
PP1-Arch was verified as a protein phosphatase by both acid molybdate extraction and thin layer electrophoresis. Soluble fraction was prepared from Sulfolobus solfataricus, from which PP1-Arch was purified over 1OOO-fold by DE-52 ion-exchange, hydroxyapatite, gel filtration (G- 100), and Mono Q FPLC chromatography. PP1-Arch was identified from the final purified sample by renaturation on an SDS-polyacrylamide gel. The molecular size of PP1-Arch was determined by both gel filtration chromatography and SDS-PAGE as 28 kDa and 33 kDa, respectively, which suggests that PP1-Arch is a monomer. PP1-Arch was found stable at temperatures as high as 90°C. Activation constants for the divalent metal ions Mn²⁺ and Ni²⁺, and the K_m for phosphocasein were determined. Myosin light chain was found to be a substrate for PP1-Arch in vitro. EDTA, Cu²⁺, Zn²⁺, P_i' and PP_i were shown to be inhibitors of PP1-Arch, while many compounds known to affect eukaryotic protein phosphatase activities were found to be without noticeable effect. N-terminal and an internal peptide sequence of the enzyme were obtained. The gene for PP1-Arch was cloned by a combination of "touchdown" PCR and conventional cloning techniques. The PP1-Arch gene was sequenced on both strands, and the sequence was compared with ones from eukaryotes and bacteriophage λ. The sequence homology between PP1-Arch and PP1/PP2A/PP2B suggests that they belongs to the same genetic family. A recombinant plasmid which was derived from pT7-7 was constructed for expression of PP1-Arch. The PP1-Arch gene was expressed in E. coli and the activity of the expressed enzyme was tested and shown to be divalent metal ion-dependent. Formation of inclusion bodies of expressed PP1-Arch was demonstrated.
The role of the apparent rate constant of cross-bridge transition from the strong binding state (G app ) in skeletal muscle force production
Ward, Christopher W. (Virginia Tech, 1996)
Force regulation at the level of the actin-myosin cross-bridge (XB) can be described by a 2 state model in which the XB's cycle between a strongly bound (SB), force generating state and a weakly bound (WB), non-force generating state. This cycle can be characterized by the apparent rate constants for transition into the SB state (fapp) and returning to the WB state (gapp), Increases in XB force can be accounted for by an increase in fapp a decrease in gapp., or both. While effort towards understanding XB force regulation has focused on the notion that force production is primarily regulated by fapp the purpose of this investigation was to determine if gapp continues to force regulation at the XB and to determine whether gapp differs in,muscles with differing contractile characteristics.

Browsing by Author "Lee, John C."

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