PLASMA PROTEIN-BOUND IODINE AFTER INTRAVENOUS INJECTION OF THYROXINE IN THYROIDECTOMIZED DOGS1

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Abstract
A single dose of 500 [mu]g. of thyroxine was given to thyroidectomized dogs, and a single dose of 5000 [mu]g. was given to 1 hypophysectomized and 2 thyroidectomized dogs. After the intraven. injn. of 500 [mu]g. of thyroxine, the disappearance of protein-bound I from plasma had 2 phases. The initial rapid phase of disappearance, with an avg. half-time of 1.42 hrs., is attributed to the distr. of thyroxine into tissues and body fluids. The slower phase of disappearance of protein-bound I from plasma following distr. had an avg. half-time of 24.6 hrs. This phase is believed due to metabolic destruction and excretion of thyroxine. When a dose of 5000 [mu]g. of thyroxine was admn., the character of the curve of disappearance of protein-bound I from plasma indicates multiple regressions. Analysis of these curves indicates that the rate of distr. (mean half-time = 1.16 hrs.) was about the same as with the smaller dose of 500 [mu]g. The rate of disposal, with a half-value time avging. 9.4 hrs., was very much more rapid than the rate of disposal after injn. of 500 [mu]g. of thyroxine. Six detns. of thyroxine space in 3 dogs avgd. 36.9 [plus or minus] 11.8% of body wt. Admn. of cortisone did not influence the rate or distr., vol. of distr. or the rate of disposal of injd. racemic thyroxine in a thyroidectomized dog.