Thyroid and gonadal hormones in feather regeneration of the redheaded bunting, Emberiza bruniceps

Abstract

AbstractThe 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‐T4 and triiodothyronine‐T3) 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 T4. The rate of feather regeneration was faster during December and June when endogenous T4 levels were high and slower during July/August and March/April when levels of circulating T4 were relatively low. Such a relationship was, however, not observed with T3. Results of administration of T4 and T3 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 T4 on the rate of feather regeneration and on the number of regenerated papillae than T3. Injection of propylthiouracil (PTU—an effective inhibitor of peripheral conversion of T4 to T3 in the redheaded bunting) in thyroidectomized birds that were also receiving T4, 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 T4 is more important than T3 for feather regeneration in redheaded buntings and that the effects of castration are due to alterations in thyroid function.