Chickens from lines artificially selected for juvenile low and high body weight differ in glucose homeostasis and pancreas physiology
Sumners, Lindsay Hart
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Early pancreatectomy experiments performed in ducks and pigeons at the end of the 19th century revealed that avians, unlike mammals, do not display signs of diabetes. Relative to mammals, birds are considered hyperglycemic, displaying fasting blood glucose concentrations twice that of a normal human. While circulating levels of insulin are similar in avians and mammals, and structure and function of the insulin receptor are also conserved among vertebrate species, birds do not experience deleterious effects of chronic hyperglycemia as observed in mammals. Understanding avian glucose homeostasis, particularly in chickens, has both agricultural and biomedical implications. Improvement of feed efficiency and accelerated growth in poultry may come from a greater understanding of the physiological processes associated with glucose utilization in muscle and fat. The chicken has also recently been recognized as an attractive model for human diabetes, where there is a great need for preventative and therapeutic strategies. The link between type 2 diabetes and obesity, coupled with the inherent hyperglycemic nature of chickens, make chickens artificially selected for juvenile low (LWS) and high (HWS) body weight a favorable model for investigating glucose regulation and pancreas physiology. Oral glucose tolerance and insulin sensitivity tests revealed differences in threshold sensitivity to insulin and glucose clearance rate between the lines. Results from real-time PCR showed greater pancreatic mRNA expression of four glucose regulatory genes (preproinsulin, PPI; preproglucagon, PPG; glucose transporter 2, GLUT2; and pancreatic duodenal homeobox 1, Pdx1) in LWS, than HWS chickens. Histological analysis of pancreas revealed that HWS chickens have larger pancreatic islets, less pancreatic islet mass, and more pancreatic inflammation than LWS chickens, all of which presumably contribute to impaired glucose metabolism. In summary, results suggest that at selection age, there are differences in pancreas physiology that may explain the differences in glucose regulation between LWS and HWS. These data pave the way for future studies aimed at understanding the developmental regulation of endocrine pancreas function in chickens, as well as how aging affects homeostatic control of blood glucose in chickens.
- Doctoral Dissertations