Hormonal regulation of follicle-stimulating hormone receptors in the testes of Japanese quail

The effects of gonadotrophins and testosterone on the binding of ¹²⁵I-labelled rat FSH to a testicular homogenate of hypophysectomized Japanese quail have been studied. Hypophysectomy resulted in rapid decrease in the binding of FSH per testis but did not change the binding per unit testicular weight, suggesting a decrease in FSH binding per Sertoli cell. Injections of NIH-FSH-S12 to hypophysectomized birds (100 μg/day) for 5 days induced hypertrophy of Sertoli cells and 2.2-fold increase in the binding of FSH per Sertoli cell. Injections of testosterone to hypophysectomized birds (5.0 mg/day) for 5 days also increased the binding of FSH per Sertoli cell 2-3-fold, but did not change the cell size. Combined administration of FSH and testosterone induced 4.4-fold increase in the binding of FSH per Sertoli cells and also marked hypertrophy. The Scatchard plot analysis of the binding of FSH to the testicular preparation of hypophysectomized birds treated simultaneously with FSH and testosterone showed that the number of the binding sites, but not the affinity of the binding, was increased by the hormone treatment. Synergistic action of FSH and testosterone was observed in the increase of not only the number of the FSH binding sites but also in testicular weight and the number of spermatogonia and spermatocytes. These results indicated that FSH receptors in the testes of Japanese quail are regulated by FSH and testosterone. It is suggested the FSH acting synergistically with testosterone increases the sensitivity of the testis to FSH itself by increasing FSH receptors. This self-potentiation mechanism may enable rapid testicular development in photo-stimulated birds and mammals at puberty.