Cell replication in the islets of langerhans of adult rats: effects of pregnancy, ovariectomy and treatment with steroid hormones.

It was possible to vary the replication rate of cells in the islets of Langerhans of adult rats. The rate of incorporation of [3H]thymidine into islet DNA was increased at 12 days of pregnancy to 2.3-fold and at 19 days of pregnancy to 1.3-fold that in control rats. Ovariectomy, which leads to lowered plasma levels of ovarian steroids, induced a significant and unexpected increase in the rate of thymidine incorporation into islets; treatment of ovariectomized rats with 2 micrograms oestradiol/rat per day for 3 days reversed this upward trend. When islets from normal rats were cultured with certain combinations of steroid hormones including progesterone and oestradiol or with insulin secretagogues, with the exception of glucose, a decreased rate of DNA synthesis was usually found compared with that in control rats. Since treatment with steroid hormones inhibited incorporation of [3H]thymidine into islets from ovariectomized rats and directly reduced incorporation into tissue-cultured islets from normal rats in vitro, it was concluded that increased levels of steroid hormones were not responsible for the higher rate of regeneration of islet cells in pregnant rats. However, a striking correlation between levels of blood glucose in vivo and DNA synthesis in islets in vitro has been observed.