DISAPPEARANCE RATE OF EXOGENOUS THYROTROPHIN FROM THE BLOOD OF NORMAL AND HYPOPHYSECTOMIZED RATS12

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Abstract
The levels of TSH in the blood of intact and hypophysectomized male rats were detd. at various time intervals (6 min., 1 hr., 5 hrs., 22-24 hrs., 46-48 hrs.) after a single intracardial injn. of purified hormone previously bioassayed by serial dilution with the stasis tadpole method. Values for TSH recoveries in the sera (similarly tested in the tadpole) indicate that the rate of disappearance of hormone from the blood was greater in intact than hypophysectomized animals. In intact rats, the serum concn. of TSH fell logarithmically against time, with 29-30% of the expected concn. recoverable at the 6-min. interval, but with less than 3% and 1% detectable at 1 and 5 hrs., respectively. TSH levels in the blood of hypophysectomized animals were approx. 10-fold greater at the 1- and 5-hr. intervals, and hormone was still detectable in the circulation 24 hrs. after injn.