Immunocytochemical Localization of Estrogen Receptor in Various Anterior Pituitary Hormone Cells of Adult Male and Female Rats.

Estrogen receptor (ER) -bearing parenchymal cells in the rat anterior pituitary gland were identified and classified immunocytochemically using antibodies against various anterior pituitary hormones as well as ER. The percentage of the respective pituitary hormone-positive cells among the total number of ER-immunoreactive cells (RH/ER) was higher in the order of somatotrophs, lactotrophs and gonadotrophs in both sexes. The proportion of ACTH- and TSHβ-positive cells among ER-immunoreactive cells was below 3%. The proportion of somatotrophs was significantly higher in the male. The RH/ER ratio of gonadotrophs and lactotrophs fluctuated during the sexual cycle of the female and both were highest at the proestrus stage.The present study provides immunocytochemical confirmation of many reports that estrogen regulates LH and PRL secretion via an estrogen receptor protein in all hormone-producing cells such as gonadotrophs and lactotrophs, and suggests that somatotrophs, which are more abundant in ER-immunoreactive paren-chymal cells, may also be under the control of estrogen.