Inhibitory action of porcine follicular fluid upon granulosa cell luteinization in vitro: assay and influence of follicular maturation.

Luteinization assessed morphologically by cAMP release stimulated by luteinizing hormone (LH) and by progesterone secretion was observed in pig granulosa cells cultured in defined medium supplemented with follicular fluid from small or large (6-12 mm) follicles. Granulosa cells luteinized in 20% serum or 20% fluid from large follicles but they did not luteinize and became necrotic in 20% fluid from small (1-2 mm) follicles. Similarly 50% serum in medium 199D or 50% fluid from large follicles permitted about the same amount of cAMP release after 48 hours of culture when cells were incubated 20 minutes with 1 mcg LH/ml; but in comparison 50% fluid from small follicles inhibited cAMP synthesis 71% and 20% fluid from small follicles inhibited cAMP less so. Fluid taken from ovaries in Cycle Days 2-15 had the same effect as that from ovaries in Cycle Days 16-21 if follicle size was the same. No change could be obtained by extracting follicular fluids with charcoal or petroleum ether. Fluid from small follicles depressed progesterone secretion into the medium 50-95% after 2 days in suspension of monolayer cultures compared with fluid from large follicles. The results indicate that small follicles contain an inhibitor or large follicles a stimulant of luteinization.