ACTIVIN-A INHIBITS OXYTOCIN AND PROGESTERONE PRODUCTION BY PREOVULATORY BOVINE GRANULOSA-CELLS INVITRO

The aim was to examine the effect of activin on luteinization of preovulatory bovine granulosa cells in vitro. Bovine activin-A was found to inhibit the production of oxytocin (OT) and progesterone by bovine granulosa cells from individual preovulatory follicles cultured in serum-free medium. The minimal response on OT production (25% inhibition) occurred with 0.1-1 ng/ml activin-A and the maximal inhibition (83%) occurred with 10 ng/ml activin-A after 2-3 days in culture. Progesterone showed a similar response (30% inhibition for 0.1-1 ng/ml and 74% for 10 ng/ml). Inhibin production was not consistently effected by activin-A. Inhibin (75 U/ml) had no detectable effect upon OT or progesterone production. When activin-A was withdrawn from the cell culture after 72 h and the incubation continued for a further 72 h, a recovery in OT was seen on day 4 and 5 after activin-A doses of 0.1-1 ng/ml, but not after higher doses (3 and 10 ng/ml). Progesterone did not show a recovery, but the levels remained constant for 3 days (0.1 and 0.3 ng/ml activin-A) or for 1 day (1-10 ng/ml activin-A) and then fell to control levels by day 6 of culture. We conclude that bovine activin-A has an autocrine action on bovine granulosa cells in vitro, to inhibit basal production of OT and progesterone, consistent with the role of activin-A in delaying the process of luteinization. © 1990 by The Endocrine Society.