Studies on the influence of sex hormones on glucose tolerance and insulin secretion in the rat

Abstract

This thesis examines certain aspects of the general hypothesis that 'sex hormones participate in the physiological regulation of carbohydrate metabolism'. Studies in female rats at different stages of the oestrous cycle, following ovariectomy and during advancing age indicate that enhanced sexual endocrine function is associated with an improvement of glucose tolerance and an elevation of plasma insulin levels.This interpretation is substantiated by observations that treatment of ovariectomized females with oestradiol, progesterone and a preparation of gonadotrophins produces similar alterations of glucose metabolism and the circulating insulin pool. Evidence is presented that oestradiol and progesterone induce these changes within six hours, and that progesterone, but not oestradiol may directly promote pancreatic insulin secretion within this period, Testosterone does not appear to exert a significant influence on glucose tolerance in male rats, although there is a tendency for this hormone to reduce plasma insulin levels. Characteristic sex differences of glucose tolerance and circulating insulin levels have been detected and their possible relationship with the prevailing sex hormone environment is discussed. The mechanisms through which sex hormones may effect glucose tolerance and insulin levels, and the implications of these processes are considered with respect to their importance during different reproductove states in the female.