Thyroid and gonadal hormones in feather regeneration of the redheaded bunting, <i>Emberiza bruniceps</i>

Abstract

Abstract The time lag in the appearance of the first feather papillae (rate of feather regeneration) was studied after monthly depluming of the redheaded bunting ( Emberiza bruniceps ). Results indicate that the rate of feather regeneration varies over an annual time scale. When a comparison was made between monthly changes in levels of plasma thyroid hormones (thyroxine‐T 4 and triiodothyronine‐T 3 ) in redheaded buntings (Pathak and Chandola, '82a) and the rate of feather regeneration, the rate of regeneration showed a distinct correlation with levels of circulating T 4 . The rate of feather regeneration was faster during December and June when endogenous T 4 levels were high and slower during July/August and March/April when levels of circulating T 4 were relatively low. Such a relationship was, however, not observed with T 3 . Results of administration of T 4 and T 3 separately, in normal as well as in thyroidectomized birds; in different doses; and during different phases of the annual cycle, indicate a strikingly greater influence of T 4 on the rate of feather regeneration and on the number of regenerated papillae than T 3 . Injection of propylthiouracil (PTU—an effective inhibitor of peripheral conversion of T 4 to T 3 in the redheaded bunting) in thyroidectomized birds that were also receiving T 4 , resulted in even faster rates of feather regeneration. Thyroidectomized birds receiving saline had no feather regeneration. Castration led to a slow rate of feather regeneration during May/June only. During this period thyroid activity of the redheaded bunting is known to be significantly influenced by gonadal hormones; this influence is not apparent during January/February or August. Injections of testosterone neutralized the effects of castration. It is concluded that T 4 is more important than T 3 for feather regeneration in redheaded buntings and that the effects of castration are due to alterations in thyroid function.