[Biosynthesis and secretion of insulin under the effect of an antibiotic of the tetracycline group].

Formation and secretion of insulin during administration of tetracycline hydrochloride in vivo and in vitro were studied in experimental rat Langerhans islets isolated by enzymatic digestion with collagenase. Insulin secretion was determined by radioimmunoassay, insulin biosynthesis was assessed from 3H-leucin incorporation into the de novo formed proteins of the islets with insulin immunoreactivity (proinsulin plus insulin). Injection of the antibiotic in a dose of 25 mg/kg intraperitoneally for 10 days did not change the functional activity of beta-cells--the rate of insulin formation and secretion at low and high glucose concentrations in the incubation medium. Higher doses of the antibiotic applied in vivo (100 mg/kg intraperitoneally for 10 days) and in vitro (100 mumol, 2-hour incubation) inhibited the glucose-stimulated (15 mmol) insulin secretion but exerted no effect on insulin biosynthesis. The possible importance of ionophore properties of the antibiotic, that changes the concentration of intracellular Ca2+ in the mechanism of dissociated action of tetracycline hydrochloride on insulin formation and secretion, as well as the practical significance of the data obtained are discussed.