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

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 con-comitant 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 breed-ers, 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. WW7"E have been investigating the interrela-» • tionship of the vascular and related de-generative changes associated with obesity, diabetes, hypertension, and hyperadrenocorti-cism as these may be expressed by abnormal hypothalamic-pituitary-adrenal-gonadal activ-ity. In this same connection, we have re-ported the development of hyperlipidemia, hyperglycemia, hypertension and arteriosclero-sis, accelerated aging and death in male and female Pacific salmon (and Rainbow Trout) as they fight their way upstream in their fren-zied effort to spawn (Robertson, Krupp, Thomas, Favour, Hane, & Wexler, 1961; Rob-ertson & Wexler, 1960). We have found that repeatedly-bred male and female rats will de-velop obesity, hyperlipidemia, hyperglycemia, hypertension, hyperadrenocorticism, arterio-sclerosis, accelerated aging, and premature death, usually associated with acute myocardial infarction, in parallel with the number and frequency of their pregnancies or copulatory activity (Wexler, 1964a, b). In our ancillary investigations we found that repeatedly-bred male and female rats develop progressively worsening islet hyperplasia, beta