Induction of functional prolactin receptors by follicle-stimulating hormone in rat granulosa cells in vivo and in vitro.

Abstract

The role of follicle-stimulating hormone (FSH) in the regulation of prolactin (PRL) receptors in granulosa cells was investigated. After 2 days of incubation in a chemically defined medium, the specific binding of lz51- PRL to cultured granulosa cells was low (1.01 + 0.23 fmol/106 cells). In contrast, addition of FSH (100 ng/ ml) caused a 3-fold increase in the specific binding of lz51-PRL (3.86 f 0.33 fmol/106 cells). In viuo administra- tion of FSH for 2 days caused a similar 3-fold increase in 12’I-PRL to granulosa cells. FSH (1 pg) and human chorionic gonadotropin (hCG; 1 pg) did not displace 12’I-PRL, but human growth hormone (hGH) was as effective as PRL in competing for 12’I-PRL binding sites. The effect of PRL on progesterone, 20a-dihydropro- gesterone, and estrogen biosynthesis was investigated. During a B-day incubation in defined media containing 100 nM androstenedione (aromatase substrate), control and PRL-treated cells from unprimed animals secreted negligible amounts of steroid hormones. However, after pretreatment for 2 days in vitro with FSH (100 rig/ml), these cells responded to PRL (1 gg/ml) by showing a 5- fold and 3-fold increase in progesterone and 2Oa-dihy- droprogesterone production, respectively. In contrast, PRL did not increase estrogen formation by such cells, indicating the PRL effect was specifically coupled to progestin synthesis. The stimulatory effect of PRL on progesterone synthesis was dose-related; the minimal and apparent maximal effective doses of PRL were 30 rig/ml and 1 pg/ml, respectively. A dose-related in- crease in 20a-dihydroprogesterone was also observed with PRL but it was less than the progesterone re- sponse. Comparable steroidogenic responses to PRL were observed with granulosa cells pretreated with FSH for 2 days in viva, suggesting our in vitro obser- vations reflect a normal physiological event. The pro- gesterone/20a-dihydroprogesterone ratio was signifi- cantly decreased (a-fold) by PRL over control and FSH- treated cells, suggesting PRL decreased 20a-hydroxy- steroid dehydrogenase activity. These results demonstrate that 1) FSH stimulates the formation of specific PRL receptors in granulosa cells in vitro and in uiuo, 2) the FSH-induced PRL receptors