Differential responses to hypothalamic testosterone in relation to male puberty

Abstract

Intrahypothalamic implantation of small quantities of crystalline testosterone propionate severely retarded puberal development of the testes and accessory sex glands in immature male rats. Only implants in the median eminence region were effective. Similar implants in adults had no noticeable effect on the testes, and even much larger ones in adults had less effect on both testes and accessory glands than did the small implants in prepuberal animals. The pituitary FSH (follicle-stimulating hormone) content in prepuberal rats with testosterone implants appeared to be markedly reduced. No consistent changes in pituitary FSH were noted following implantation at puberty or in adults. In all experiments, control groups received cholesterol implants in the median eminence. The basal hypothalamus showed essentially no growth after the age at which these experiments were commenced. The results support the concept of an increase in the "set point" of a hypothalamic, testosterone-sensitive, negative feedback controller occurring at the time of puberty in the male.