Increased clearance rate of plasma thyroxine accompanies estradiol-induced vitellogenesis in male Japanese quail

Four days after giving 16 mumol estradiol-17 beta (E2) per 100 g body weight to male Japanese quail, the thyroids of these quail accumulated twice as much 125I as did the thyroids of control quail. Plasma thyroxine concentrations were 7.38 +/- 45 (SE) ng/ml (n = 16) for the E2-treated quail and 3.38 +/- .53 ng/ml (n = 16) for the controls. Clearance rates of plasma thyroxine were 534 ng thyroxine/100 g/day for the E2-treated quail and 234 ng/100 g/day for the control quail. The E2 may have increased the metabolism of thyroxine in these male quail and, by inference, stimulated a twofold increase in the rate of synthesis and secretion of thyroxine.