Prolactin-mediated progesterone secretion by cultured rat granulosa cells: regulation by purified human glycoprotein hormones and their subunits.

The effects of purified alpha- and beta-subunits of human glycoprotein hormones on initial luteinization and subsequent prolactin-mediated progesterone responses of cultured rat granulosa cells were studied. Granulosa cells, obtained from immature female rats 50 h after PMSG treatment, were incubated for 24 h in control medium lacking added hormones or in medium containing hCG or the alpha- or beta-subunit of human (h) FSH, LH, CG, or TSH at 0.1, 0.5, and 1.0 microgram/ml. Cultures were maintained subsequently for 6 days in medium containing 1.0 microgram/ml bovine PRL (bPRL), with medium changes every 48 h. Indices of luteotropic stimulation in response to bPRL were provided by 1) elevated progesterone concentrations determined by RIA of spent media samples, and 2) cytoplasmic lipid accumulation assessed by osmium tetroxide staining following fixation of monolayers after 7 days of culture. Progesterone concentrations in media from cultures incubated in 0.5 or 1.0 microgram/ml hCG were 6-fold higher than in cultures incubated in control medium, while those in media from cultures incubated in 0.5 or 1.0 microgram/ml hFSH alpha, hLH alpha, hCG alpha, hTSH alpha, hLH beta, or hCG beta (but not in hFSH beta or hTSH beta) were from 2- to 4-fold higher than those in control cultures. This enhancement was not evident when subunits were added to the incubation media at the lowest concentration. Progesterone secretion corresponded directly with the degree of cytoplasmic osmiophilia. These results suggest that the alpha-subunit of each of the glycoprotein hormones as well as the beta-subunit of hLH and hCG have the ability to promote progesterone secretion during initial luteinization and to regulate subsequent PRL-mediated steroidogenesis by rat granulosa cells in vitro. Furthermore, these effects are greater than can be accounted for by potential contamination of subunit preparations with undissociated hormones, as demonstrated by dose-response curves.