Thyroid Metabolism of Chickens: 2. Estimation of Thyroxine Half-Life in Plasma

Abstract

Chicks were exposed to constant 7.2° or 32.2° C. temperatures for various periods. Plasma radioactivity was partitioned into organic and inorganic components at various intervals up to 6 hours after injection of thyroxine I-131 or NaI-131. The inorganic component was elevated significantly at all bleedings 2 hours or more after injection of thyroxine I-131. The organic component never exceeded 4 percent of the radioactivity following NaI-131 injection. These results suggest that thyroxine half-life should be determined within the first 2 hours after thyroxine I-131 injection if total plasma radioactivity is used.In the thyroxine half-life measurements, blood was collected during the first hour after thyroxine I-131 injection and plasma radioactivity was measured by liquid scintillation spectrometry. Thyroxine half-life was significantly decreased within 1 day of exposure to 7.2° C. Chicks reared to 44 days of age at 7.2° and 32.2° C. had thyroxine half-lives of 34.1 and 52.6 minutes, respectively.