FOLLICLE-STIMULATING-HORMONE (FSH) RECEPTORS AND FSH-RESPONSIVE ADENOSINE 3',5'-CYCLIC-MONOPHOSPHATE PRODUCTION IN PORCINE GRANULOSA-CELLS DECLINE WITH FOLLICULAR-GROWTH

Comparison of binding of I-125-porcine FSH to porcine granulosa cells from small and large ovarian follicles indicated that binding is dependent on both time and temperature. At 37 C, binding of ligand is more than four times higher in cells from small follicles than in cells from large follicles within 30 minutes of the start of incubation. Binding to cells from both small and large follicles is more stable for a longer period of time at 20 C than at 37 C. Equilibrium saturation binding analysis of I-125-pFSH binding indicated that binding is saturable and of high affinity. Granulosa cells from small and large follicles have similar affinities for I-125-pFSH. However, granulosa cells from small follicles have 4.7-times as many FSH receptors as granulosa cells from large follicles. The sensitivity and responsiveness of the adenylyl cyclase system to FSH were assessed by incubating cells from small and large follicles with increasing concentrations of FSH in a defined medium containing isobutylmethylxanthine (1 mM), an inhibitor of phosphodiesterase. Granulosa cells from small follicles are more sensitive to FSH and have a greater cAMP response to FSH than granulosa cells from large follicles. Thus, both active FSH receptors and FSH-responsive adenylyl cyclase activity decline during follicular growth.