Developmental changes in the binding of follicle-stimulating hormone (FSH) to testicular preparations of mice and the effects of hypophysectomy and administration of FSH on the binding.
Changes with age in testicular FSH binding and the effects of hypophysectomy and administration of FSH on FSH binding were studied in mice. The binding per unit testicular weight reached a peak at 10-20 days of age and it rapidly decreased during 20-37 days. The total binding per two testes increased from 4 days of age, reaching a peak at 31 days, and decreased thereafter when the testis still continued growing. Scatchard plot analyses of the binding showed that the equilibrium constant of dissociation (Kd) was about 3 X 10(-10) M regardless of age, and the changes in FSH binding were due to changes in the number of binding sites. Hypophysectomy at 90 days of age induced a significant decrease in the testicular weight, but the concentration of FSH binding sites markedly increased 16 days after the operation. In hypophysectomized mice the total number of FSH binding sites was increased 1.8-fold as compared with intact mice. In contrast, hypophysectomy induced a decrease in the total number of LH-binding sites. Injections of 100 micrograms NIH-FSH-P-2 for 10 days to hypophysectomized mice significantly decreased the concentration and the total number of FSH binding sites as compared with those in saline-injected hypophysectomized mice. These results suggest that FSH reduces its own receptors in the testis of mice.