A radio-immunoelectrophoretic assay for human growth hormone

Abstract

A method for the measurement of growth hormone in human plasma is described based on the inhibition of the reaction between I131-labelled growth hormone and rabbit antiserum to purified human growth hormone. The extent of the reaction is determined by electrophoresis and radioactivity measurements and can also be determined by gel-filtration on Sephadex G-200. The method permits the assay of multiple samples of plasma by using small volumes of plasma or plasma extract at 2 concentrations. The lower limit of sensitivity for purified growth hormone is 0-07 [mu]mg/ml and this concentration is measured with maximum percentage error (P 0.05) of + 50%. The precision of the measurement of growth hormone in plasma has been calculated and the quantitative sensitivity of the method derived from results given by its routine use. At a concentration of 0.22 [mu]mg/ml of plasma, growth hormone is significantly different from zero (P 0.05) and measured with a maximum percentage error (P 0.05) of [plus or minus] 50%. Evidence for the specificity of the method has been obtained by comparing the inhibition of the reaction by purified growth hormone and by a variety of plasma samples, from the effect of animal sera in the assay, from the recovery of endogenous growth hormone in a simple extraction procedure, and from the results of assays in normal and pathological plasma. A protein cross-reacting with antibodies to growth hormone which is present in plasma from women and monkeys during pregnancy and in placentas at term was noted. The slope of the inhibition curve obtained with monkey pituitary extract and plasma from a non-pregnant monkey is identical with that obtained from human pituitary extracts and suggests that the method could be applied to the measurement of growth hormone in plasma from non-pregnant monkey. The removal of an immunologically and biologically inactive component present in all growth hormone preparations studied by gel-filtration is reported.