Effects of testosterone on the testes of sexually quiescent pheasants: evidence for a negative feedback mechanism.

1. The testicular response of sexually quiescent pheasants to testosterone was studied by injection of testosterone alone and in combination with chicken pituitary extract (CPE) for 20 d. 2. Testosterone alone caused a significant decrease in testicular weight, whereas CPE alone caused a significant increase. In combination testosterone and CPE caused no significant change in testicular weight, suggesting a suppression of the stimulatory effect of CPE by testosterone. The depressive effect of testosterone on testicular weight may be explained on the basis of negative feedback mechanism. 3. CPE alone stimulated the production of spermatogonia and primary spermatocytes whereas testosterone, alone or with CPE, did not elicit such a response. The lack of response of the germinal epithelium to testosterone may indicate the ineffectiveness of the hormone in initiating spermatogenesis in pheasants.