BIOASSAY OF THYROTROPIN1

Abstract
Studies were conducted on the uptake of I131 by the rat thyroid following a single intravenous injection of thyrotropin. Dose-response relationships were determined utilizing thyroxine- treated, thyroxine plus propylthiouracil-treated, thyroid powder prefed, and hypophysectomized rats as assay animals. The thyroxine-treated rat was least sensitive of all. The hypophysectomized rat responded linearly over the range of 0.625-2.5 milliunits (U.S.P) of thyrotropin. The thyroxine plus propylthiouracil-treated rat was less sensitive than the hypophysectomized animals, but responded over a greater range of dosage 2.5-160 milliunits). The thyroid powder prefed rat was most convenient to deal with and responded linearly over the range of 0.5-160 milliunits.