Abstract
A growth hormone radioreceptor assay (RRA) was developed using the 100,000 g pellet from pregnant cortisone-treated rabbit liver homogenate, the 125 I hGH binding being specifically and completely displaced by unlabelled hGH. Sensitivity was 0.2 ng. Comparing the GH levels found by this method and by radioimmunoassay in normal sera, the mean RRA/RIA ratio was 0.84 ± SEM 0.07 (range 0.70/0.93). In 11 out of 16 primordial dwarfs the RRA/RIA ratio was in the normal range; it was lower in 2 and higher in 3. But in a number of samples from primordial dwarfs the curve of displacement of labelled GH from the receptor did not parallel the standard curve. This phenomenon was not due to anti-hGH antibodies, it was not induced by addition of insulin and was not modified when variable amounts of hGH were added to these sera. It may be concluded 1/ that serum levels of GH estimated by RRA are generally lower than by RIA; 2/ that individual discrepancies are found in primordial dwarfs; 3/ that the serum from certain primordial dwarfs modifies the affinity of GH for the receptors.
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