Effects of pregnancy and progesterone and/or oestradiol on the insulin secretion and pancreatic insulin content in the perfused rat pancreas.

Progesterone and oestradiol treatment of ovariectomized rats was administered leading to plasma steroid concentrations comparable to those of the pregnant rat. In these experimental conditions oestradiol enhanced insulin secretion but progesterone had little effect on B cell response to glucose (0.8 g/l and 1.4 g/l) of the perfused pancreas. At low glucose concentration (0.8 g/l) neither of the two steroids, added to the perfusion medium, had any effect on insulin release of the pancreas of the castrated animals; oestradiol exerted a facilitating action on glucose stimulation (1.4 g/l); progesterone had no effect. During pregnancy biphasic insulin secretion was enhanced, but pancreatic hormonal content was only increased at term. Neither oestradiol nor progesterone treatment changed pancreatic insulin content. It is concluded that oestradiol acts on insulin release at pancreatic level directly, whereas progesterone influences insulin release by causing insulin resistance.