Some Properties of the Interaction of Follicle Stimulating Hormone with Bovine Granulosa Cells and Its Inhibition by Follicular Fluid1

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Abstract
The binding of radiolabeled human follicle stimulating hormone (125I-hFSH) to bovine granulosa cells collected from follicles at varying stages of maturation as judged by size was studied. Specific binding was time and temperature dependent, reaching its maximum after 2 h of incubation at 37.degree. C and pH 7.5. Specific binding was saturable with respect to 125I-hFSH and receptor concentrations and could be inhibited by unlabeled purified human FSH (25 ng = 50% inhibition) and bovine FSH (35 ng = 50% inhibition), but not by large (5000 ng) amounts of bovine LH [lutropin], TSH [thyrotropin], GH [somatotropin], prolactin or human ACTH. Specific binding of 125I-hFSH to granulosa cells from large follicles (> 6 mm) was at least as great as to granulosa cells from medium (3-6 mm) and small (< 3 mm) follicles. Fluid from bovine follicles of all sizes significantly inhibited binding of 125I-hFSH to granulosa cells in a dose related manner. The amount of FSH binding inhibition (FSH-BI)/ml of fluid from large follicles was approximately 2-fold greater than that from small follicles and contained approximately 100-fold higher levels of FSH-BI activity than did small follicles by virtue of increased fluid volume. FSH-BI activity was markedly reduced by dialysis, passing a membrane having a MW retention of 8000 daltons and could be detected in the dialysate. The chemical nature of the dialyzable follicular fluid FSH-BI is not known, although it was not adsorbed by charcoal or soluble in diethyl ether.