Biphasic effect of testosterone on spermatogenesis in the rat.

The mechanism by which treatment with testosterone produces azoospermia was investigated in adult male rats. Serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels were measured in rats treated with testosterone in order to determine whether testosterone in doses which suppressed only LH, and not FSH, would produce atrophy of the germinal epithelium. Rats received injections of testosterone enanthate (TE), (.3, 3, or 30 mg), 3 times weekly for 6 weeks. Low dose TE (.3 mg): 1) decreased mean testis weight by 42%, 2) produced atrophy of the germinal epithelium, and 3) suppressed serum LH but not FSH. High dose TE (3 and 30 mg): 1) did not affect testis weight, 2) did not affect the histology of the germinal epithelium, and 3) did suppress both LH and FSH. It is concluded that testosterone induces germinal atrophy by suppressing serum LH concentrations and subsequent androgen production by the Leydig cells, thereby decreasing the normally high intratesticular levels of androgen which are necessary for maintenance of the germinal epithelium. When these high concentrations of androgen are restored by treatment with pharmacologic doses of testosterone, no disturbance of the germinal epithelium occurs despite suppression of both LH and FSH.