Identification of the progesterone target cells in the female baboon pituitary gland.

The identification of target cells for progesterone was conducted on pituitary glands obtained from long-term ovariectomized and adrenalectomized female baboons that had been injected with 3H-ORG 2058 (16 alpha-ethyl-21-hydroxy-19-nor-4-pregnene-3,20-dione; Amersham Corp). Binding sites were localized using autoradiography alone or in conjunction with immunocytochemistry. The synthetic progestin was primarily found over nuclei of cells in the pars distalis and pars intermedia, although a small population of pituicytes also bound the 3H-ORG 2058. The majority of steroid-sensitive cells in the pars distalis were gonadotrophs. These observations suggest a role for progesterone in the regulation of not only the gonadotropins but also those hormones secreted by the cells of the pars intermedia.