Influence of Lactation upon Pancreatic Islet Function

The activity of adenylate cyclase, its reponsiveness to NaF and forskolin, the activity of the protein kinases A and C, and the oxidation of exogenous d-glucose, l-leucine, and l-glutamine were all higher in pancreatic islets removed from lactating, as distinct from nonlactating, rats. Yet, the release of insulin evoked by d-glucose or the association of l-leucine and l-glutamine was lower in the islets obtained from lactating animals. The lactation-induced decrease in secretory activity was not attributable to a change in the insulin content of the islets, was not corrected by exposure of the islets to theophylline or forskolin, and was also observed in response to stimulation by Ba2+. The rapidly exchangeable islet Ca pool, as estimated from the basal value for 45Ca net uptake, was severely decreased in lactation. Moreover, a hypoglycemic sulfonylurea, which stimulated islet 45Ca net uptake much more markedly in lactating than nonlactating animals, provoked, in association with 12-O-tetradecanoylphorbol...