ENHANCED CELL-PROLIFERATION BY HYPERPROLACTINEMIA IN BOTH EXOCRINE AND ENDOCRINE PANCREAS IN MICE

Effects of hyperprolactinemia induced by ectopic anterior pituitary gr afting on the pancreas were studied in male SHN mice. After pituitary grafting, the weight of pancreas rapidly increased. A similar increase in pancreatic weight was observed during lactation, a condition assoc iated with elevated prolactin levels. Results of DNA and protein assay s revealed that the increase in pancreatic weight in both pituitary-gr afted and lactating mice was mainly due to the increase in the cell nu mber, because the total DNA content per pancreas was greater in these mice than the controls. An increase in fluid volume or hypertrophy of cells also contributes to the weight increase; in contrast, the DNA an d protein contents per unit tissue weight decrease. The rate of DNA sy nthesis determined by 5-bromo-2'deoxyuridine labeling was higher both in acinar cells and islet B cells in pituitary-grafted mice than in th e controls. Thus, hyperprolactinemia stimulates cell proliferation in exocrine pancreas as well as endocrine islets. The effect of prolactin seems to be indirect on acinar cells, because only B cells showed pro lactin immunoreactivity in the mouse pancreas. In addition, insulin mi ght not be a mediator of the prolactin effect on acinar cells, because the serum insulin level in pituitary-grafted mice failed to show any change.