Diurnal sensitivity of the testes to exogenous testosterone propionate in sexually regressed whitethroated munia Lonchura malabarica.

: The testes in different groups of whitethroated munia (Lonchura malabarica) were studied following exogenous treatment of testosterone propionate (1 mg/100 g body wt./day) at 06.00 h or 14.00 h or 22.00 h for 15 consecutive days during the quiescent phase of the annual testicular cycle. The testicular conditions in each group of testosterone treated and appropriate control (administered only with the vehicle of hormone at corresponding time-points) group of birds were analyzed by the studies of paired testicular weight, seminiferous tubular diameter, spermatogenetic index, and cytology of the testicular germ cells. The results of the study revealed that exogenous testosterone was stimulatory to the testicular functions irrespective of the time of treatment. The gametokinetic response of the testes to exogenous testosterone also did not show any statistical difference among the birds treated at different hours of the day. The present study demonstrates for the first time that the responses of the testes to exogenous testosterone during the post-breeding phase in an annual testicular cycle of a wild bird does not vary with the time of administration.