Effect of insulin on endocrine pancreas function during late pregnancy in the rat

To partly or completely satisfy the increasing demand for insulin, pregnant rats were infused SC with human insulin (2.4 or 4.8 IU/day) from day 14 to day 20 of gestation. Cyclic control rats underwent the same procedure of 6 days of insulin-treatment. During the treatment all groups of rats were hypoglycaemic, but foetal survival was not affected. The low dose treatment prevented the characteristic rise of the insulin response to a glucose challenge during pregnancy, both in vivo and in vitro, while the high dose treatment suppressed the insulin response, as well as the pancreatic insulin content. The insulin responses and insulin contents of pregnant rats were higher than those of the corresponding cyclic control rats. These results support the hypothesis that during gestation the increased insulin demand, due to the actions of placental hormones, is the cause of the increased insulin secretion. However, it cannot be excluded that direct effects of placental hormones on the islets of Langerhans are also involved.