Modulatory effect of acetylcholine on gonadotropin-stimulated human granulosa cell steroid secretion

The aim of this study was to explore the direct action of acetylcholine on gonadotropin-stimulated progesterone (P) and estradiol (E(2)) secretion of human granulosa cells (GCs) cultured in serum-free medium. Human GCs were isolated from preovulatory follicular fluid aspirated from 22 women undergoing in vitro fertilization at the University Women's Hospital of Tübingen. The production of progesterone and E(2) was measured in the presence and absence of acetylcholine, carbachol, atropine, luteinizing hormone (LH) or follicle-stimulating hormone (FSH) using radioimmunoassay. Statistical analysis of the data was performed by ANOVA and Newman-Keuls test. Administration of acetylcholine or carbachol (10(-5) M) resulted in a significant increase in P and E(2) secretion. This response was specifically blocked by the muscarinic receptor antagonist atropine. Similarly, carbachol resulted in a significant increase in P and E(2) output, though the response to it was somewhat reduced when compared to that evoked by acetylcholine. Acetylcholine did not show any additive effect on LH-stimulated P secretion, while it augmented the stimulatory effect of FSH on P release. In contrast, carbachol markedly diminished the stimulatory effect of LH on P secretion, while it caused no change in FSH-induced P output. When administered together, acetylcholine did not modify the stimulatory effect of FSH on E(2) secretion, however, it markedly elevated LH-induced E(2) output. Similar to this, carbachol significantly increased LH-induced E(2) release, however it decreased FSH-stimulated E(2) secretion. We suggest that acetylcholine has a direct modulatory effect on gonadotropin-stimulated steroid production of GCs, an effect that is mediated via muscarinic receptors. This effect may have a physiological role in the regulation of GC function during the menstrual cycle.