An evaluation of a bioassay method for thyroid stimulating hormone and its application to Citellus richardsoni

Abstract

An in vitro bioassay for thyroid stimulating hormone (TSH) based upon the TSH-stimulated release of I131 was evaluated. Significant error was not introduced by the method of pipetting aliquots of incubation medium in order to estimate I131 activity. Incubation times for uptake and release agree with those suggested by Bottari's group. While per cent uptake and absolute release of I131 were significantly related to the weight of tissue incubated, per cent release was not, and weighing of tissue before incubation was not necessary. It was found that storage of TSH in plasma at -10° C did not preserve TSH activity, thus fresh samples were used. U.S.P. reference standard TSH was quantitatively recovered from horse serum, rat plasma, and Richardson ground squirrel plasma, with no apparent inhibition and with the linear range of the log-dose response lying between 5--200 ImU/100 mI. Assay results are reported for male Holtzman strain rats. C. richardsoni plasma from summer and winter squirrels and one spring squirrel was assayed with the following results which support indirect findings of other investigators: summer, 34 ImU/100 ml; winter, 4 ImU/100 ml; spring, 116 ImU/100 mI.