Effects of corticosterone, metapyrone, and ACTH on testicular function at different stages of the breeding cycle in migratory redheaded bunting, Emberiza bruniceps.

To study the seasonal reproductive responses, corticosterone (0.2 and 2 micrograms/day), metapyrone (0.6 mg/day), and ACTH (0.25 IU/day) were administered in male redheaded bunting, Emberiza bruniceps, during different phases of the annual gonadal cycle. All of the three treatments inhibited gonadal growth during the preparatory phase, suggesting that during the early stage of annual gonadal growth, an optimum level of the hormones of pituitary-adrenal axis is essential. In the progressive and breeding phase, while corticosterone administration had no effect, metapyrone inhibited the annual gonadal development, suggesting the necessity of increasing or increased adrenal steroid hormone during this phase. In the regressive phase, while corticosterone enhanced the rate of gonadal regression, metapyrone treatment did not allow the gonad to regress. Further, ACTH administration induced full breeding condition in the regressing gonad. It is suggested that while a higher level of adrenal steroids and a low ACTH (by exogenous corticosterone) may enhance the testicular regression, moderate levels of ACTH (caused by exogenous metapyrone) did not allow regression and increased ACTH levels (by exogenous ACTH) caused full development of the regressing gonad. Thus the sensitivity of the neuroendocrine-gonadal axis not only varies in response to photoperiod, but the reproductive system also responds differently to pharmacological administration of the above three hormones and drugs during different phases of the breeding cycle.