RADIOIMMUNOASSAY OF GROWTH HORMONE IN HUMAN PLASMA

Abstract

ABSTRACT The double antibody radio-immunoassay (pre-precipitation technique) for immunoreactive growth hormone (IRHGH) in human plasma has been evaluated on the basis of dilution and recovery experiments as well as by the investigation of accuracy and reproducibility. Given optimal conditions for the precipitation reaction, the method seems suitable for determination of plasma IRHGH. No cross-reaction between the precipitating antiserum and human gammaglobulin was demonstrated. Furthermore, by using an incubation period of 6 days for the reaction between 125I-HGH and the precipitated HGH antibodies, no serum factor influencing this reaction could be demonstrated. The results of the plasma IRHGH determinations were shown to be independent of the percentage of the radioactive degradation products present in the tracer HGH. The lower detection limit is better than 0.39 ng/ml. The cumulated within-assay coefficient of variation was between 4–7% and the cumulated between-assay coefficient of variation 10%. By using gel filtration, IRHGH in the plasma was shown to be nonhomogeneous when considering molecular weight. The normal fasting values in the ambulatory state was (Mean ± sd) ng/ml: Men 1.48 ± 0.33; women 3.83 ± 3.47. During the insulin tolerance test the mean peak plasma IRHGH was lower in children than in adults (0.02 > P > 0.01). It is suggested that this is due to the influence of sex steroids in adult subjects.