Effect of progesterone on insulin secretion in the rat.

Implants of progesterone resulted in an increased amount of insulin in plasma in response to intravenous administration of glucose in the rat. Isolated islets of Langerhans from progesterone-treated animals showed a greater maximum secretory response to glucose than islets from control animals but their sensitivity to low concentrations of glucose was unchanged. Theophylline increased glucose-induced secretion of insulin to a greater extent in progesterone-treated than in control rats and also produced a greater increase in the concentration of cyclic AMP in isolated islets from hormone-treated animals. These results suggest that the effect of progesterone on insulin secretion may be mediated by a change in cyclic AMP levels in the beta cell. The possible role of progesterone in increasing the secretion of insulin in pregnancy is discussed.