The effect of follicular fluid protein(s) on gonadotropin-modulated secretion of progesterone in porcine granulosa cell cultures

Abstract

Porcine granulosa cells from medium-sized follicles (2 to 5 mm in diameter) were cultured (100,000 cells per culture) with various concentrations of a 12,500 to 16,000 molecular weight protein fraction isolated from follicular fluid. To these cultures pregnenolone (10−5 mol/L) and either human chorionic gonadotropin or porcine follicle-stimulating hormone were added. The conversion of pregnenolone to progesterone was used to determine 3-β-ol-dehydrogenase activity in the granulosa cells. Follicular fluid protein alone caused a biphasic response in the production of progesterone. Follicular fluid protein in the concentration of 167 μg/ml caused a tenfold increase in the production of progesterone, whereas the 500 μg/ml concentration caused a return to baseline levels. Although porcine follicle-stimulating hormone induced a dose-response increase in the production of progesterone, human chorionic gonadotropin produced no change in the levels of progesterone. Low doses of follicular fluid protein acted synergistically with low doses of porcine follicle-stimulating hormone to increase granulosa cell secretion of progesterone. However, high doses of follicular fluid protein inhibited the low-dose stimulation by porcine follicle-stimulating hormone of the production of progesterone. High doses of porcine follicle-stimulating hormone (10 μg/culture) overcame both the low-dose enhancement and the high-dose inhibition of follicular fluid protein on granulosa cell secretion of progesterone. Thus follicular fluid protein may be an important paracrine modulator of steroidogenesis stimulated by follicle-stimulating hormone in the porcine granulosa cell.