[Influence of glucose infusions on proinsulin and insulin syntheses in the islands of langerhans in the rat].

Experiments on RNA synthesis and the observation of an increased secretion of proinsulin during stimulated synthesis of insulin in islets of Langerhans in vitro led to the supposition that insulin synthesis in vivo may be increased to a higher extent than synthesis in vitro. This investigation evaluates the effect of long time infusions of glucose on the synthesis of proinsulin and insulin in islets of Langerhans from the rat. The following results were obtained: 1. the rate of synthesis of proinsulin and insulin increased due to glucose infusions by a factor of 2 after 6 hours and by a factor of 4 after 24 hours; 2. prolonged infusion led to a decrease of insulin synthesis and serum insulin concentrations; 3. the turnover of proinsulin into insulin remained unaffected by the glucose infusion; 4. a specific stimulatory effect on the synthesis of one of the two insulins of the rat was not observed. The conclusion was made, that glucose in vivo stimulates enzyme induction, followed by increased RNA synthesis and mitotic activity. These combined factors lead to an increased insulin synthesis.