[Studies on the suppression mechanism of follicle-stimulating hormone (FSH) release by porcine follicular fluid].

To study the mechanism of inhibin action on the release of FSH, the effect of porcine follicular fluid (pFF) on the LH-RH binding to the anterior pituitary cells as well as cyclic AMP (cAMP) and diacylglycerol (DAG) content in the pituitary cells were examined in monolayer cultures of the rat anterior pituitary cells. The suppression of the binding of labeled LH-RH to the pituitary cells was not affected by pFF. Neither the LH-RH receptor concentration nor the affinity of LH-RH with the binding sites was affected by pFF according to the Scatchard analysis. A dose-related decrease in FSH content in the conditioned media was observed in the pFF-treated culture wells, whereas luteinizing hormone levels remained unaltered by pFF. There was no significant difference between pFF-treated and untreated groups in cAMP or DAG content in the rat anterior pituitary cells. These data may indicate that inhibin has no effect on the LH-RH receptor, suggesting the presence of its own receptor on the gonadotropes. Messenger system(s) other than A-kinase and C-kinase systems in the cells may be involved in the suppression of FSH by inhibin.