ACTIVIN AND INHIBIN SECRETION BY CULTURED PORCINE GRANULOSA-CELLS IS STIMULATED BY FSH AND LH

Follistatin-free activin and inhibin levels were measured in the culture medium of porcine granulosa cells by a competitive protein binding assay and N-fragment RIA, respectively. Cultures were maintained for 6 days in MEM containing 10% fetal calf serum. FSH and HCG (1-1,000 IU/L) were added on day 2 to cultures containing 1 x 10(5) cells/ml and the medium was changed every 2 days. Granulosa cells secreted a large amount of progesterone, which indicated their luteinization. Activin and inhibin were both secreted throughout the 6 day culture period. Both of them increased equally in response to FSH and HCG in a dose-dependent manner on day 4, but t.heir responses became discrepant on day 6, when the activin response decreased while the response of inhibin increased. This study demonstrated that cultured porcine granulosa cells secrete both activin and inhibin under the control of FSH and LH. The activin response was lost before that of inhibin, suggesting the role of activin at an earlier stage of luteinization.