Effect of ovariectomy, thyroidectomy and of thyroxine treatment on the plasma level of corticosterone of the female Japanese quail.

Corticosterone was determined by means of competitive protein binding in the plasma of ovariectomized, thyroidectomized, ovariectomized and thyroidectomized, thyroxin-treated, corticosterone-treated and control Japanese quails, exposed to short or long photoperiod. Female birds exposed to short photoperiod possessed a slightly (not significantly) higher plasma corticosterone level than male ones. In photostimulated animals, however, the plasma corticosterone level showed no sex difference. Unlike in male quails, photostimulation did not enhance corticosteronaemia in the female ones. Corticosterone level was decreased by ovariectomy in both short-day and long-day birds. It was decreased by thyroidectomy and increased by thyroxine treatment in short-day birds, while the same interventions were ineffective in photostimulated ones. The data obtained point to that thyroxine treatment enhances, while the lack of ovarian sexual steroids decreases the plasma corticosterone level of female Japanese quails. Comparison of data obtained from ovariectomized + thyroidectomized birds shows that light may be responsible for elevated corticosteronaemia per se.