Serum Insulin Changes in Male Rats Associated With Age and Reproductive Activity

Abstract

A comparison has been made of the serum insulin, glucose, free fatty acids, and corticosterone levels, as well as histopathologic changes, of young and old virgin males vs. young and old breeder males. Both the old rats and the male breeder rats manifested significant hyperinsulinemia concomitant with their obesity. Male breeders which had sired 5 to 8 litters had greatly elevated serum insulin levels, whereas male breeders which had sired 8 or more litters, but were in decline as breeders, manifested reduced circulating insulin levels. Glucose levels were commensurately the same in all groups, but free fatty acid levels were greatly elevated in the old rats and in the breeder rats. The older subjects were found to have subcapsular adrenal adenomata and islet hyperplasia, whereas the breeder rats also manifested abnormal adrenal histopathology, but displayed shrunken and fibrotic islets.