Abstract
The depression of 131I concentrating activity in propylthiouracil (PTU) blocked guinea pig thyroid slices has been utilized for the assay of TSH. The control iodide space was determined for each slice after 16 hr equilibration; TSH doses were then added and allowed to act for 10 hr. The effect metameter (the ratio of final to control T/M) eliminates variation due to non-uniformity of the mass of functional tissue assigned to each tube. High sensitivity and initial uptakes of 50–75% required for maximal precision are achieved by using thyroid tissue from guinea pigs treated chronically with PTU and withdrawn from goitrogen 72 hr before assay. The dose range for optimal precision extends from 1 to 64 μU International Standard TSH and from 2 to 16 μU human Research Standard A TSH (final concentration/ml in incubation medium). The limit of detection for TSH in unknown samples is about 0.5 mU/100 ml. Forty animals were tested in the assay to determine the homogeneity of the animal population with respect to se...
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