Inhibition of luteinizing hormone/human chorionic gonadotropin binding to porcine granulosa cells by a follicular fluid protein(s)

Abstract

Previously, we evaluated the effects of a follicular regulatory protein(s) on granulosa cell follicle-stimulating hormone (FSH) receptors during short-term culture. No demonstrable effect on porcine granulosa cell FSH binding capacity was found. Here, we assessed the effects of follicular regulatory protein(s) on porcine granulosa cell human chorionic gonadotropin (hCG) binding capacity. Follicle regulatory protein was prepared from porcine follicular fluid by saturated ammonium sulfate precipitation, dialysis, lyophilization, and pseudoligand affinity chromatography. Receptor assays were performed with the use of porcine granulosa cells and hCG as the radioligand. After 48 hours in vitro, there was an apparent follicular regulatory protein(s)-induced diminution in overall specific granulosa cell 125I-hCG binding compared to the 24-hour determination. After 72 hours, control cultures and those which received FSH alone had significantly greater specifically bound 125I-hCG compared to cultures which were treated with either follicular regulatory protein(s) or FSH plus follicular regulatory protein(s). This disparity became more apparent by 96 hours of culturing. Granulosa cells which received FSH alone or control cultures had significantly greater specifically bound 125I-hCG compared to granulosa cell cultures treated with either follicular regulatory protein(s) or FSH plus follicular regulatory protein(s). Furthermore, follicular regulatory protein(s) produced a dose-response inhibition of hCG binding. When considered together with previous observations of follicular regulatory protein(s)-associated inhibition of granulosa cell aromatase in both human and porcine granulosa cells, these data suggest that follicular proteins may play a major role in the intraovarian modulation of folliculogenesis.