REGULATION OF ISLET BETA-CELL PROLIFERATION BY PROLACTIN IN RAT ISLETS

This study examined the effects of prolactin on beta-cell proliferation in pancreatic islet of Langerhans. Insulin secretion and beta-cell proliferation were significantly increased from neonatal rat Islets cultured for 4 days in the presence of either 500 ng/ml ovine prolactin (oPRL) or rat prolactin (rPRL). These effects could be prevented by including anti-oPRL serum in the culture media. Although insulin secretion and beta-cell proliferation were slightly higher during the first 24 h of exposure to rPRL, maximal response was observed after 4 days for Insulin secretion and 6-10 days for beta-cell proliferation. The initial mitogenic response of beta-cell to rPRL occurred by the limited recruitment of nondividing beta-cells into the cell cycle and by most daughter cells proceeding directly into additional cell division cycles. Subsequently, the maximal effect of rPRL on beta-cell proliferation was maintained by a higher rate of recruitment of previously nondividing beta-cells into cell cycle with only one fourth of the daughter cells continuing to divide. These observations are difficult to reconcile with the proposal that a limited pool of beta-cells capable of undergoing cell division exists in islets. Instead, these observations suggest that individual beta-cells are transiently re-entering the cell cycle and dividing infrequently in response to rPRL. In this case, the majority of the beta-cells would not be expected to be in an irreversible G(o) phase. We also demonstrated that the effects of rPRL on beta-cell proliferation occur at normal serum glucose concentrations and are affected by inhibitors of polyamine metabolism. Additional studies on the effects of rPRL on beta-cells should provide important information on the regulation of beta-cell proliferation during conditions of increased insulin demand.