Cellular Regulation of Follicle‐Stimulating Hormone (FSH) Binding in Rat Seminiferous Tubules

Abstract

Stage‐specific binding of follicle‐stimulating hormone (FSH) was measured in rat seminiferous tubules. The binding in single‐point assays was over 3‐fold higher (P < 0.05) in stages XIII to I than in stages VI to VII of the epithelial cycle. No difference was found between the equilibrium association constants (Ka) of FSH binding in stages XIV to IV (10 ± 1.9 × 109 1/mol) and VII to VIII (9.2 ± 0.6 × 109 1/mol, mean ± SEM, n = 5). In another experiment, the testes were dosed locally with 3 Gy of 4 MV x‐irradiation to selectively lower the number of spermatogonia. After irradiation, FSH binding in staged seminiferous tubule segments was measured when the desired types of spermatogenic cells were reduced in number. Seven days after irradiation when differentiating spermatogonia and preleptotene spermatocytes were reduced in number, FSH binding was decreased in all stages of the cycle, but the cyclic variation remained. Seventeen days after irradiation when intermediate and type B spermatogonia and spermatocytes up to diplotene of stage XIII snowed low numbers, FSH binding was decreased in all stages of the cycle and the stage‐dependent variation disappeared. At 38 days when pachytene spermatocytes and early spermatids were reduced in number, similar results were found. But at 52 days postirradiation when all spermatids were low in number, FSH binding was slightly elevated compared with days 17 and 38. There were no significant differences in serum FSH or LH levels between irradiated and non‐irradiated animals. These findings suggest that all spermatogenic cell types may stimulate FSH binding in the Sertoli cells. Spermatocytes and spermatids seem to be responsible for the stage‐dependent variation.