Date of Award


Document Type

Honors Thesis (Open Access)


Colby College. Chemistry Dept.


Catherine R. Bevier

Second Advisor

Julie Millard


Blood glucose homeostasis is tightly regulated in mammals. Insulin and exercise both stimulate glucose uptake into muscle cells via the GLUT4 transporter protein by independent pathways. Insulin triggers a tyrosine kinase pathway, but the mechanism stimulated by exercise is unknown. Discovering the mechanism may provide new therapeutic techniques for people with diabetes mellitus. While mammals have been studied extensively, research on a different model may elucidate aspects of this lesser known pathway. Reptiles rapidly deplete glycogen stores during bursts of activity and produce lactate as a byproduct of anaerobic metabolism. Lactate undergoes gluconeogenesis within muscle tissue, rather than liver tissue, to quickly replenish glycogen stores. Lactate is a preferred substrate for gluconeogenesis; thus, glucose uptake is inhibited. Since exercise has a significantly different effect on metabolism in reptiles, a reptilian model may provide novel information as to how exercise stimulates glucose uptake in mammals. Anolis sagrei were treated with combinations of exogenous insulin and exercise. Blood glucose, blood lactate, muscle glycogen, liver glycogen and muscle GLUT4 were measured. There was no significant treatment effect on levels of post-exercise blood glucose, however, levels of blood lactate increased significantly following exercise. Muscle glycogen was generally lower following exercise, though liver glycogen was not significantly different. GLUT4 was not detected. Finally, there was no difference in the level of any monitored metabolite following insulin injection. It appears that (1) gluconeogenesis occurs in muscle rather than liver tissue; (2) muscle contractions do not stimulate glucose uptake; (3) insulin may not affect glucose metabolism; (4) an isoform of the GLUT4 transporter protein may not exist. Future studies should compare the relative activities of effectors in reptiles and mammals following exercise to help elucidate the mechanism of the contraction-stimulated glucose uptake pathway in mammals.


Insulin, homeostasis, glucose, lactate metabolism

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