Absence of exendin-4 effects on postprandial glucose and lipids in the Gila monster, <Emphasis Type="Italic">Heloderma suspectum</Emphasis> |
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Authors: | Carolyn M Christel Dale F DeNardo |
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Institution: | (1) School of Life Sciences, Arizona State University, Tempe, AZ 85287-4601, USA |
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Abstract: | Circulating nutrients serve as energy resources for functioning tissues throughout the body. While the tight regulation of
plasma nutrients has been extensively studied in mammals, investigations into specific metabolic regulators in reptiles have
been limited and have revealed conflicting results. The peptide exendin-4, which was isolated from the saliva of Gila monsters,
Heloderma suspectum, has demonstrated prolonged plasma glucose-lowering properties in mammals. Although exendin-4 has often been labeled a venom
protein, circulating plasma levels of exendin-4 have been shown to increase in response to feeding. Because exendin-4 has
glucose-regulating effects in mammals, we hypothesized that post-prandial elevation in circulating exendin-4 levels in Gila
monsters reduces plasma glucose and triglycerides. To examine the effect of exendin-4 on circulating nutrients, we measured
plasma glucose, triglyceride, and cholesterol levels of Gila monsters in response to one of four treatments: fed live mice
(a natural post-prandial increase in exendin-4), force-fed dead mice while anesthetized (no post-prandial exendin-4 increase),
force-fed dead mice while anesthetized and injected with exendin-4 immediately after feeding (exogenous increase in exendin-4),
and force-fed dead mice while anesthetized and injected with exendin-4 24 h after feeding (delayed exogenous increase in exendin-4).
After prey ingestion, glucose and triglyceride levels increased significantly over time in all treatment groups, but there
was no significant treatment effect. Plasma exendin-4 levels showed significant time and treatment effects, but did not correspond
to glucose and triglyceride levels. Our results demonstrate that plasma nutrient levels in Gila monsters respond relatively
slowly to feeding and that exendin-4 does not have the same effect on circulating glucose in Gila monsters as it does in mammals.
Further studies are necessary to determine whether circulating exendin-4 has an alternate role in regulating other components
of energy metabolism such as nutrient uptake rate in the small intestine. |
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Keywords: | Exendin-4 Glucose Triglyceride Heloderma suspectum Nutrient regulation |
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