A decrease in FSH receptors of granulosa cells during follicular maturation in the domestic hen

The follicles of the ovary in the domestic hen are arranged in a hierarchy. Responsiveness of the adenylyl cyclase enzyme system of the granulosa cells to FSH decreases as follicles proceed towards ovulation. To test the hypothesis that this decline in FSH responsiveness could be the result of a decrease in FSH receptor numbers, an FSH receptor assay was characterized for chicken granulosa cells and used to measure receptor number and affinity of the largest (F1), third largest (F3) and fifth largest (F5) follicles removed 18 h before ovulation. The numbers of binding sites for F1, F3 and F5 follicles (n = 4) were 0.22 +/- 0.05, 0.5 +/- 0.14 and 1.22 +/- 0.27 pmol hormone bound/mg protein respectively, and were significantly (P less than 0.001) different among follicles. The apparent association constants for the F1, F3 and F5 follicles were not different and had a value of 23.4 +/- 4.9 litres/nmol (n = 12). Our results indicate that FSH receptor numbers decrease in granulosa cells without a change in affinity as follicles approach ovulation. The decrease in FSH receptor numbers is associated with the reported decline in FSH-stimulated steroidogenesis and adenylyl cyclase activity which occurs during follicular maturation.