Activin-A inhibits progesterone production by macaque luteal cells in culture

Since inhibin is produced during the luteal phase of the menstrual cycle in women and nonhuman primates, the primate corpus luteum (CL) may be a local site of inhibin/activin action. This study was designed to determine whether inhibin or activin altered steroidogenesis by macaque luteal cells in vitro. Luteal cells were obtained by enzymatic dispersion of CL from rhesus monkeys at midluteal phase of the menstrual cycle. Cells (2 × 10⁴/0.2 mL) were cultured in wells coated with extracellular matrix from bovine corneal endothelial cells in Dulbecco's modified Eagle's medium/F-12 medium (1:1 vol/vol) + insulin (2 ng/mL), transferrin (5 ng/mL), H₂SeO₃ (0.25 nmol), and aprotinin (10 μg/mL). Various concentrations (0-400 ng/mL) of recombinant human-inhibin-A, recombinant human-activin-A or human CG (hCG) (100 ng/mL; CR123) alone or in combination with inhibin or activin were added to the culture media (n = 5 Exp). Media were changed daily for 4 days and progesterone (P) concentrations were determined by RIA. Inhibin exposure did not alter P levels compared to that of control (untreated) cultures. In contrast, activin (10-400 μg/ mL) suppressed P production (P < 0.05) below controls and inhibin-treated cultures by days 3 and 4. Exposure to hCG increased P levels throughout culture (9 x control levels by day 4; P < 0.05). hCG-stimulated P production was unaltered by inhibin, whereas activin (50-400 ng/mL) reduced (maximal inhibition of 40%; P < 0.05) hCG-stimulated P production by day 4 of culture. Cell number on day 4 was not altered by any dose of inhibin or activin, but the number of cells staining for 3β-hydroxysteroid dehydrogenase was reduced (P < 0.05) by 32.9 ± 2.6% in activin-treated cultures. Since P levels declined during culture in all treatment groups, in a second series of experiments (n = 4), luteal cells were cultured for 4 days with or without hCG (100 ng/mL) and low density lipoprotein (LDL; 100 μg/mL) ± 0-400 ng activin/mL. P production in the presence of hCG + LDL was greatly enhanced compared to other treatment groups and was sustained during days 2-4 of culture. Activin at doses of 50-400 ng/mL suppressed (maximal inhibition of ≈35%; P < 0.05) hCG + LDL-stimulated P production on days 3 and 4. These results suggest that the primate CL is a target for activin action to suppress luteal cell activities, including gonadotropin-regulated, lipoprotein-mediated steroidogenesis.