Progesterone Stimulates Pancreatic Cell Proliferation in Vivo

(Correspondence should be addressed to A Nieuwenhuizen) Treatment of cyclic and pregnant rats with progesterone stimulates cell proliferation within the islets of Langerhans. It was investigated whether this effect of progesterone depends on sex and/or the presence of the gonads or the presence of oestradiol. For this purpose, Silastic tubes containing progesterone were inserted s.c. in intact and gonadectomized male and female rats, and in gonadectomized female rats treated with oestradiol. After 6 days of progesterone treatment, rats were infused for 24 h with 5-bromo-2 0-deoxyuridine (BrdU) and dividing cells were identified in pancreatic sections by immunostaining for BrdU. Progesterone treatment increased islet-cell proliferation in intact male and female rats (P<0.05), but not in gonadectomized male and female rats or in gonadectomized female rats supplemented with oestradiol. Furthermore, in intact male and female rats, progesterone treatment also stimulated cell proliferation in extra-islet pancreatic tissue (P<0.05). Identification of the proliferating cells, by double-immunocytochemistry, revealed that progesterone treatment stimulated proliferation of both a and b cells within the pancreatic islets. In extra-islet pancreatic tissue, progesterone treatment stimulated proliferation in both duct (cytokeratin 20-immunoreactive) an