Thyroxine and triiodothyronine turnover in the chicken and the bobwhite and Japanese quail

Abstract

Except for the data of Heninger and Newcomer (1964) on the t 1 2 of T 4 and T 3 in cardiac tissue of chickens and brief reports on the t 1 2 of T 4 in blood plasma of chickens (Tata and Shellabarger, 1959; Hendrich and Turner, 1967) and Japanese quail (McFarland et al., 1966) , no information has been found in the literature on the degradation of thyroid hormones in birds. In the present investigations, thyroxine- and triiodothyronine-distribution spaces (TDS) and biological half lives ( t 1 2 ) of the two hormones are reported. The extrathyroidal thyroxine- (ETT) and thyroid-secretion rate (TSR) from thyroxine degradation have been calculated from T 4 turnover data in the chicken, bobwhite and Japanese quail. Protein-bound iodine values (PBI) in the three species of birds are also presented. In addition, the results of TSR by thyroxine degradation are compared in chickens receiving diets adequate or deficient in iodine. Thyroxine and triiodothyronine turnover was studied in the chicken, bobwhite quail and Japanese quail. The thyroid secretion rate (TSR) as determined by this method in 7-week normal chickens, 7-week goitrogen-treated chickens, 56-week normal chickens, bobwhite, and Japanese quail, averaged 2.03, 1.59, 1.02, 2.49, and 2.78 μg/100 gm body weight/day, respectively. The TSR of iodine-deficient chickens was found to be significantly decreased. The representative biological half lives of T 4 in the blood of chickens, bobwhite, and Japanese quail were 3.25, 4.60, and 5.50 hours, respectively. The half life of T 3 in each species of birds tested is not significantly different. The representative thyroxine-distribution space (TDS) in ml/100 gm body weight of chickens, bobwhite, and Japanese quail, respectively, measured 29.39, 28.08, and 55.29. TDS/unit body weight of 56-week old chickens is significantly lower than in 7-week chickens. T 3-distribution spaces in all birds are higher than that of T 4. The representative protein-bound iodine of chickens, bobwhite, and Japanese quail were measured as 1.12, 1.76, and 1.26 μg, respectively. Increased plasma radioactivity was found in cardiac blood samples as compared to those taken by venous puncture. It is believed that this represents discharge of unchanged hormone from extrathyroidal tissues, probably the liver, in response to the withdrawal of a relatively large volume of blood. The possible role of this mechanism in regulating thyroid hormone levels is discussed.