Summer Research

* Student(s): Sarah McNeil , Angela Pagano , Hannah Stahle , Katie Lee
Advisor: David Gapp

Title: Post-prandial changes in circulating glucose, amino acids and gastrin in the American alligator


Regulation of digestion by gastrointestinal hormones is poorly understood in many subavian vertebrates, especially in reptiles. In particular, measurement of endogenous gastrointestinal hormones has been lacking as a means of correlating the rise and fall of meal-derived nutrients with the hormones regulating various aspects of digestion.

Two groups of American alligators were employed for this study, and they had not fed in the 7 days prior to the onset of the experiments. Five males (range: 2.6-6.7 kg) were used in Experiment 1, and 5 females (range: 1.8-3.4 kg) were used in Experiment 2. Zero time blood samples were taken from the dorsal sinus behind the head. The animals were then fed lab mice, and the number of mice consumed was determined for each animal. Blood samples were taken thereafter at 6, 12, 24, 48 and 72 hours. At each sampling, blood glucose was determined immediately on an automatic glucose analyzer, and plasma was prepared and stored frozen for subsequent determination of amino acids and gastrin. Total plasma amino acid concentration was measured using a ninhydrin-based assay on plasma extracts, and plasma gastrin levels were determined using a commercial radioimmunoassay kit.

In Experiment 1, modest post-prandial rises in blood glucose were observed, even in the one animal that did not feed suggesting a stress-related phenomenon. Plasma amino acids levels rose significantly within 6 hours after feeding and returned to baseline by 48 hours in the two animals that ate 1 or 2 mice, but remained elevated in the two animals that ate considerable more (6 and 13). In the animal that did not feed, plasma amino acids remained relatively unchanged. The feeding-induced rise in plasma gastrin peaked at 24 hours, but remained more elevated in the two animals that ate more mice. In Experiment 2, similar results were obtained for blood glucose values, however, values obtained for plasma amino acids and gastrin were highly variable and did not provide as clear a pattern as seen in Experiment 1.

While preliminary, these results suggest that in the alligator gastrin is rapidly released after ingestion of a meal, and the circulating level and persistence of post-prandially elevated gastrin may be related to the size of the meal ingested. Previous studies have shown gastrin to rise within 1 hour after feeding in alligators suggesting an early neural component to gastrin release in these animals. The present finding of gastrin levels related to meal size and/or the degree elevated of plasma amino acids suggest subsequent modification of the early phase of gastrin release in the alligator.

Student stipend support provided by Bristol-Myers Squibb Foundation (AP, KL) and Merck/AAAS grants (HS, SM).