Changes in levels of a LH binding inhibitor in aqueous extracts of porcine corpora lutea as a function of aging of the corpus luteum

The 30,000 x g supernatant fraction of aqueous extracts from porcine corpora lutea of old, mid and early luteal phases was investigated to determine its inhibitory activity on the binding of [ 125 I]-hCG and on progesterone secretion by granulosa cells harvested from large (6-12 mm) follicles of porcine ovaries. The extracts from old and midcycle corpora lutea had greater ability to inhibit the binding of [ 125 I]-hCG than did extracts of early luteal phase corpora lutea. During a 1 h incubation period with tracer hCG, the extracts of late and mid luteal phase corpora lutea exerted a 90% inhibition of [ 125 I]-hCG to porcine granulosa cells whereas the extract of early luteal phase corpora lutea exerted a 70% inhibition. Addition of 10% of a 30,000 x g supernatant of old corpora lutea, either directly or after removal of steroids with 0.1% charcoal, inhibited progesterone secretion 90-95% by granulosa cells of large porcine follicles grown for 2 days in monolayer culture. The addition of 1 µg ovine LH along with the extracts from old corpora lutea could not reverse the inhibitory effect. Addition of 10% of a 30,000 x g supernatant of nonluteal ovarian tissue obtained during the mid or late luteal phase inhibited progesterone secretion by cultures of granulosa cells obtained from large follicles after 2-4 days of culture (P