THE BIOASSAY OF THYROTROPIN IN SERUM1

Abstract

A bioassay technique for thyrotropin in serum was developed from that of Adams and Purves. Mice were injected with I¹³¹ and then had endogenous thyrotropin suppressed by the administration of thyroxine followed by thyroid powder. The effect of an intravenous injection of thyrotropin or the test sub-stance was measured by the percentage increase in blood I¹³¹. This had a linear relationship to the logarithm of the dose. Sensitivity of 0.025 mu., with an injec-tion volume of 0.5 ml., and an average index of precision (λ) of 0.24 were achieved With this technique thyrotropin in the sera of 6 patients with myxedema was measured. Endogenous thyrotropic activity was shown to travel on electrophoresis with gamma globulin of such sera and was also present only in the gamma globulin fraction (II) of Cohn fractions of human plasma.