Involvement of adrenal and thyroid activity in the annual testicular regression of red headed bunting (Emberiza bruniceps).

Thyroid and adrenal activities are closely associated with reproductive cyc le and any alteration in these endocrine functions may cause changes in the pituitary-gonadal axis. To understand this interrelationship during testic ular senstive phase (month of April) male birds were injected with metapyro ne(corticosterone synthesis blocks 1 mug/bird/day & 10 mug/bird/day) and ne wmercazol (thyroxine synthesis blocks 10 mug/bird/day) over a period of 12 weeks. During late breeding phase (month of August) two sets of birds havin g large gonad (photosensitive) and regressed gonad (photorefractory) were i njected with metapyrone (10 mug/bird/alternate day). Results indicate that decreased activity of both adrenal and thyroid, extended the breeding phase but rate of regression decreased only in the case of bird receiving higher level of metapyrone. However,in the second group rate of gonadal regressio n was slow only in those bird where treatment was started during photosensi tive phase. It may be suggested that optimum level of activity of adrenal a nd thyroid function are essential for termination of reproduction and any a lteration in these function may alter seasonal pattern of neuroendocrine go nadal axis.