Effects of testosterone on spermatogenesis and luteinizing hormone release in Japanese quail

Testosterone or testosterone propionate was administered to Japanese quail (Coturnix coturnix japonica) via intraperitoneal Silastic capsules to assess the role of these androgens on spermatogenesis and luteinizing hormone (LH) release. Testosterone was released from Silastic capsules at relatively constant rates and in direct proportion to capsule length. Increasing lengths of testosterone-filled Silastic capsules induced and maintained differential increments in plasma testosterone titers and caused a concomitant decline in plasma immunoreactive LH levels in castrated quail. In intact birds, testosterone implants ranging between 40 and 320 mm caused a graded reduction in paired testis weight, spermatogenic activity, and circulating LH titers, but plasma testosterone levels remained within the range noted in intact control birds. Marked increases in plasma testosterone concentrations were noted in intact birds receiving 600- and 1200-mm testosterone or 500-mm testosterone propionate implants. Importantly, paired testis weight and the relative number of germ cells were maintained at near normal levels when plasma testosterone titers were raised about 18-fold above normal. The results indicate that the continuous administration of small amounts of testosterone (about 1 mg/day) suppressed spermatogenesis by inhibiting LH release and that spermatogenesis was maintained during the continuous administration of large amounts of testosterone (about 12 mg/day) even though LH secretion remained suppressed. The present findings support the hypothesis that testosterone exerts a differential effect on the quail testis that depends, in part, upon the amount of androgen administered.