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dc.contributor.authorZiglioli, Vincenten_US
dc.date.accessioned2017-11-09T07:00:19Z
dc.date.available2017-11-09T07:00:19Z
dc.date.issued2016-05-17en_US
dc.identifier.othervt_gsexam:7634en_US
dc.identifier.urihttp://hdl.handle.net/10919/80004
dc.description.abstractBackground: Because of the vague clinical signs and limitations of thyroid function tests, misdiagnosis of hypothyroidism in dogs is common and leads to inappropriate treatment with levothyroxine. Chronic supplementation can suppress the hypothalamic-pituitary-thyroid axis (HPTA) and make it difficult to assess thyroid function following withdrawal of levothyroxine. Objectives: To determine if the HPTA is suppressed following levothyroxine administration in euthyroid dogs and the time required for resolution of any suppression. Animals: Twenty-eight healthy euthyroid dogs Methods: A prospective randomized study administering levothyroxine to euthyroid dogs with levothyroxine, for either 8 weeks (group 1) or 16 weeks (group 2). Serum concentrations of total thyroxine (T4), free thyroxine (fT4) by equilibrium dialysis, thyrotropin (TSH), and 3,5,3'-triiodothyronine (T3) were measured every 4 weeks during supplementation and for 16 weeks after levothyroxine was discontinued. Results: Mean serum T4 and fT4 were significantly higher and TSH was lower in all dogs during levothyroxine administration compared to baseline. Mean serum concentrations of T4 and fT4 in both groups and TSH in group 1, beginning 1 week after levothyroxine was discontinued, were significantly different compared to values during levothyroxine administration but not compared to baseline values. Conclusions and Clinical Importance: Suppression of the HPTA occurred during levothyroxine supplementation and mean serum T4, fT4 and TSH concentrations were not significantly different compared to baseline 1 week after discontinuation in both groups. Assessing thyroid function tests 1 week after cessation of levothyroxine will likely provide an accurate assessment of thyroid function in euthyroid dogs.en_US
dc.format.mediumETDen_US
dc.publisherVirginia Techen_US
dc.rightsThis Item is protected by copyright and/or related rights. Some uses of this Item may be deemed fair and permitted by law even without permission from the rights holder(s), or the rights holder(s) may have licensed the work for use under certain conditions. For other uses you need to obtain permission from the rights holder(s).en_US
dc.subjectCanine hypothyroidismen_US
dc.titleEffects of Levothyroxine Adminstration and Withdrawal on the Hypothalamic-Pituitary-Thyroid Axis in Euthyroid Dogsen_US
dc.typeThesisen_US
dc.contributor.departmentBiomedical and Veterinary Sciencesen_US
dc.description.degreeMaster of Scienceen_US
thesis.degree.nameMaster of Scienceen_US
thesis.degree.levelmastersen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineBiomedical and Veterinary Sciencesen_US
dc.contributor.committeechairPanciera, David Lawrenceen_US
dc.contributor.committeememberMonroe, Edwarden_US
dc.contributor.committeememberTroy, Gregory C.en_US
dc.contributor.committeememberBoes, Katie Maeen_US


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