Influence of Lactation upon Pancreatic Islet Function*

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Abstract
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-13-acetate, a greater insulin output in lactating than nonlactating rats. It is speculated that the decreased secretory activity in islets removed from lactating rats may be accounted for, in part at least, by a decreased Ca content of the islet cells. (Endocrinology118: 687–694, 1986)

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