Submitted to: Experimental Biology
Publication Type: Abstract Only
Publication Acceptance Date: February 4, 2007
Publication Date: May 1, 2007
Citation: Sweazea, K.L., McMurtry, J.P., Elsey, R.M., Starck, M., Redig, P., Braun, E.J. 2007. Hormonal control of metabolic substrate use by birds and reptiles [abstract]. Experimental Biology Meeting.
The differential use of metabolic substrates by birds is not well understood. Therefore, to clarify which substrates are preferentially utilized, studies were conducted on birds with divergent dietary habits and on a close non-avian relative of birds, alligators. Fasting plasma substrate and hormone levels were compared for Mourning doves (omnivorous), Bald Eagles, Great Horned Owls, Red-tailed Hawks, and American alligators (all carnivorous). The plasma of carnivorous birds and alligators had the highest concentrations of ketone bodies (10 to 21 mg/dl) concomitant with low levels of triglycerides (62 to 79 mg/dl) indicative of free fatty acid (FFA) utilization. Elevated FFAs have been correlated with decreased utilization of glucose and insulin resistance in mammals. This may also occur in birds as doves, eagles and hawks were less sensitive to insulin as indicated by high glucose (325 to 350 mg/dl) levels in all three species as well as increased insulin in eagles and hawks (1.1 to 1.2 ng/ml). In contrast, owls had high glucose (361 mg/dl) but low insulin (0.2 ng/ml) levels. More studies are required to determine if owls release insulin in response to a glucose load. Interestingly, previous studies have demonstrated that pancreatectomy of Great Horned Owls results in hyperglycemia and death suggesting they, like alligators and mammals, rely on insulin more than the other birds examined in this study.