Pancreatic Content of Insulins I and II in Laboratory Rodents: Analysis by Immunoelectrophoresis

Abstract

The purpose of these experiments was to determine the relative proportion of insulins I and II in the pancreas of inbred strains of mice and rats, and whether this proportion would be altered by conditions known to affect insulin biosynthesis. Rapid analysis of multiple samples was accomplished by an immunoelectrophoretic method in which insulin can be detected in crude pancreatic extracts without further purification. Insulin I was found to account for 65–76% of total pancreatic content in C3H/HeJ, C57BL/6J, and CD2F1 mice. Glucose injection produced a significant increase in insulin content, which was completely accounted for by insulin I, although fasting for 2 days had no effect. In all three strains there was either no change or a decrease in content of insulin II, while insulin I increased 77–83% (P < 0.05) of the total pancreatic insulin. To determine the effects of chronic hyperglycemia, the content of insulins I and II was measured in the pancreas of obese hyperglycemic mice and compared with that of lean littermates. Insulin content in pregnant rats was also evaluated, since pregnancy is characterized by insulin resistance and hyperinsulinemia. The results of these studies indicate that insulin I predominates in the pancreas of a variety of strains of rats and mice. More important is the observation that conditions that increase insulin production preferentially increase insulin I relative to II, suggesting independent regulation of the two genes.