Estradiol (E) treatment of spayed macaques induces progestin receptors (PR) in pituitary gonadotropes, but not lactotropes. In contrast, levels of pituitary estrogen receptors (ER) remain constant in spayed or E-treated monkeys. In monkey pituitary cultures, the number of PR-positive cells varies depending on the donor status, whereas the percentage of ERpositive cells is similar. We sought to determine whether E can directly induce PR in monkey pituitary gonadotropes in culture and to provide further evidence that monkey pituitary ER are constitutively expressed. Dispersed pituitary cells from intact or gonadectomized male and female macaques were cultured on extracellular matrix with and without E, phenol red, high or low insulin, insulin-like growth factor-I, or 5% ovariectomized mon-key serum. ER- and PR-positive parenchymal cells were irarau- nohistochemically detected with monoclonal antibodies H222 and D75 (against human ER) and B39 (against human PR). ER levels were also measured with a gradient shift assay incorporating H222. Neither the percentage of ER-positive cells nor the levels of nuclear ER were altered by donor status or by 8 days of culture in phenol red or E. In contrast, cultures from gonad- intact donors exhibited the highest average percentage of PR- positive cells. The lower number of PR-positive cells in cultures from spayed donors did not vary for 8 days on extracellular matrix without phenol red, E, insulin, or serum. E directly increased the percentage of PR-expressing cells in serum-free cultures. Addition of serum also increased the percentage of PR- positive cells. Addition of E to serum-containing cultures further increased the percentage of PR-positive cells. Neither insulin nor insulin-like growth factor-I directly affected the number of PR-positive cells, but a high level of insulin blunted the action of E on PR induction in serum-free culture. We conclude that E treatment has no obvious effect on ER expression in macaque pituitary. However, the induction of pituitary PR by E treatment of spayed monkeys can be accounted for by a direct action of E on PR gene expression in gonadotropes.
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