QUANTITATIVE EFFECTS OF THYROTROPHIC HORMONE ON I131ACCUMULATION IN THYROID AND PLASMA PROTEINS OF HYPOPHYSECTOMIZED RATS*

Abstract

Hypophysectomy in the rat markedly reduces the capacity of the thyroid to trap I131. TSH restores this capacity to normal. At the same total dose level, single injections of TSH are less effective than multiple injns. in increasing the uptake of I131 by the thyroid of the hypophysectomized rat. The form and statistics of the log dose-response curve indicate that uptake of I131 by the thyroid in hypophysectomized rats, treated with multiple injns. of TSH, is a potentially useful method of assay for the hormone. Slopes of the log dose-response curves for purified TSH and for a crude extract of hog pituitary are not significantly different. Hypophysectomy reduces the rate of accumulation of I131 in the plasma proteins of the rat. Multiple injns. of TSH restore the capacity of the plasma proteins of the rat of accumulate I131. The form and statistics of the log dose-response curve indicate that the TSH-induced increase in concn. of PBI131 in hypophysectomized rats is a potentially useful method of assay for the hormone. The slopes of the log dose-response curves for purified TSH and for a crude extract of hog pituitary tissue are not significantly different. Following admn. of small and moderately large doses of purified TSH the concn. of plasma inorganic I131 decreases as the uptake of I131 by the thyroid increases. Very large doses of TSH increase plasma inorganic I131 to abnormally high levels. Crude pituitary extract has a relatively marked effect on decreasing plasma inorganic I131 as compared to its action on uptake of I131 by the thyroid.