Binding of estradiol and 5 alpha-androstane-3 beta-17 beta-diol by the male rat enriched gonadotrope cells

Cell-specific mechanisms of estrogen receptor in the pituitary gland

Analysis of the mechanism of action of estrogen receptor shows protein and mRNA polymorphism within distinct pituitary receptor-positive cells. The lactotropes exhibit unique properties in these mechanisms that distinguish them from gonadotropes. Therefore, this cell type constitutes an especially interesting model in the male as well as in the female for estrogen receptor studies.

5 alpha-DHT metabolism in monolayer cultures of distinct pituitary cell populations

5 alpha-Dihydrotestosterone (DHT) metabolism into 5 alpha-androstane-3 alpha, 17 beta-diol (alpha-diol) and 5 alpha-androstane-3 beta, 17 beta-diol (beta-diol) was studied in monolayer cultures of distinct cell populations from prepubertal male rats pituitaries. Cells were characterized through immunocytochemistry with the various antihormone antisera. Centrifugal elutriation was used to prepare a gonadotrope-enriched population "G" and a gonadotrope-depleted population "L", containing most lactotropes and somatotropes. Using centrifugation on Percoll gradient, two sub-populations, P1 and P2, were prepared by further fractionation of the "L" population. Cells were incubated for 48 h with [3H]DHT (1 microM, sp. act. 0.9 Ci/mmol) and metabolites extracted from the whole cell and medium. DHT was metabolized to about the same extent (30-40%) in all cell fractions. Compared with unfractionated population, the conversion of DHT into alpha-diol increased significantly in the P1 fraction, consisting of lactotropes, somatotropes and highly depleted in gonadotropes. This increase was lower in the somatotrope-enriched P2 fraction in which the amount of lactotropes was similar to P1 but that of gonadotropes slightly higher. In contrast, the conversion of DHT into alpha-diol decreased significantly in the "G" population compared with total or "L" fractions, whereas androstanedione formation, low in every population, increased significantly. The increase in alpha-diol formation could be related either to the decrease of gonadotropes or to a role of non-immunoreactive cells. As the beta-diol formation was constant in all cell types, the beta-diol/alpha-diol amount increased significantly in gonadotropes. Then, beta-diol and DHT could be both active steroids in gonadotrope regulation inasmuch as specific binding sites were identified for these two steroids. It can be concluded that DHT action at the pituitary level is subject to complex control mechanisms involving a specific balance of its metabolites in each particular cell type.

Antiestrogen binding within different pituitary cell populations. Comparison with androgen and estrogen receptors

Gonadotrope-enriched populations were prepared from 42-day old male rats by centrifugal elutriation. They contained 4.8 +/- 0.7% of the cells, 51 +/- 10% of the LH and less than 3% of the PRL (n = 4). Gonadotrope-depleted fractions were also obtained that contained most of PRL cells. Specific antiestrogen binding sites (AEBS) were quantitated in these populations after destruction of estrogen receptor. Results showed the presence of a distinct, specific high affinity binding site for antiestrogen in dispersed pituitary cells and in enriched fractions. However, AEBS are not specific of a pituitary cell type. Thus, AEBS appear different from estrogen receptors in pituitary gland: by the thermal stability of AEBS, by the localization of AEBS in particulate material, by the uniform distribution of AEBS in different populations which differ markedly for E2 binding sites. Whereas the ratio of binding AE/E2 averaged 11.4 in the initial cell suspension it reached only 2.9 in the gonadotropes. The dissociation constants for AEBS were in the same range (1.16 - 2.27 X 10(-9) M) for the different populations.