Effect of corticosterone upon insulin biosynthesis and storage by isolated rat Langerhans islets

A rapid inhibitory effect of corticosterone upon glucose- or leucine-induced insulin release being established, steroid action upon insulin biosynthesis of rat Langerhans islets was studied as a function of time. Islet proinsulin and insulin content was reduced after two hours of incubation in presence of corticosterone (0.2 mg/l) with a 16.7 mmoles/l glucose stimulation. L (-) [4-5(3)H] leucine incorporation into proinsulin and insulin was lowered at all time (points examined: 1, 2 and 3 hours). Incorporation ratio between proinsulin and insulin remained stable, so an interaction at the proinsulin biosynthetic level may be possible. Corticosterone had no effect upon biosynthesis of other islet proteins. Our data suggest that the corticosterone inhibition of insulin biosynthesis is specific.