Pancreatic Islet Cells in Preobese Yellow Avy/- Mice: Relation to Adult Hyperinsulinemia and Obesity

Abstract

Plasma insulin levels in yellow Avy/- mice begin to increase before the animals are overtly obese. Are the elevated insulin levels in yellow mice primary or secondary to the subsequent obesity? Elevated blood insulin levels in young preobese mice, due to synthesis and release of insulin by increased number of beta cells, would stimulate lipogenesis, resulting in excess lipid deposition and subsequent peripheral insulin resistance. Examination of this possibility was the objective of this study. The beta, alpha, and delta cells in the pancreata of 7-, 14-, and 21-day-old male yellow Avy/A and agouti A/a (BALB/c x VY)F1 hybrid mice were counted with immunohistochemical/morphometric techniques. The insulin and glucagon concentrations in pancreata from male and female mice of the same ages and genotypes were also assayed. In the 21-day-old male mice, the mean number of beta cells/pancreas was significantly greater in the yellow mice than in the agouti mice; however, insulin content and body weight were the same. This suggests that increased beta cell proliferation in yellow mice precedes any detectable genotype-specific increase in pancreatic insulin content or body weight.