Ultrastructural evidence of progesterone receptor by immunochemistry

Antiserum against purified chick oviduct non-transformed "8S"-progesterone receptor has been used for detecting progesterone receptor in rat pituitary cells at the ultrastructural level after immunochemical reaction according to Sternberger. In prepubertal (21-day-old) and adult (diestrus) female rats, the gonadotropic, lactotropic and somatotropic cells were positive, but not the corticotropic and thyreotropic cells. In all positive cases, the progesterone receptor-like antigen was found in both the cytoplasm and the nucleus. Two hours after progesterone administration to immature rats, there was an increase of receptor-like antigen in nuclei of gonadotropic cells. These results and the immunological controls related to antibody specificity give the first evidence of progesterone receptor at the ultrastructural level. They remarkably show that its distribution in pituitary cells parallels the distribution of the estradiol receptor.