Effect of Gonadectomy and Steroid Treatment on the Receptor-Binding Activity and Immunoreactivity of Serum and Pituitary FSH in the Adult Rats of Both Sexes

Abstract

The receptor binding activity (R) and immunoreactivity (I) of serum and pituitary FSH were measured in normal, gonadectomized, and gonadal steroid-treated rats of both sexes employing radioreceptor assay and radioimmunoassay, respectively, and R/I ratios were analyzed. At 11 weeks of age, R/I ratios of serum and pituitary FSH were significantly higher in normal females than in males. From 11 to 13weeks of age, the ratios of both FSH further increased in females, while in males, the ratio of serum FSH decreased and that of pituitary FSH increased. Orchiectomy caused an increase in the ratio of serum FSH, while ovariectomy caused a decrease, so the ratios in the gonadectomized animals of both sexes became almost equal, suggesting the secretion of a gonadectomy type FSH in these animals. Both testosterone propionate (TP) and estradiol benzoate (EB) treatments decreased the ratios of serum FSH in gonadectomized rats. However, TP and EB had an effect opposite on the ratio of pituitary FSH in these rats, i.e. TP caused a decrease, while EB caused an increase. This effect was more obvious in females than in males. These observations indicated that the presence and absence of the gonads, and the gonadal steroids influence not only the quantity but also the quality of FSH. The changes in the quality of the hormone are discussed in relation to its multiplicity.