Regulation of Receptor by Homologous Hormone Enhances Sensitivity and Broadens Scope of Radioreceptor Assay for Human Growth Hormone

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Abstract
In standard competitive binding assays (including radioreceptor assays) unlabeled ligand (hormone) competes with labeled ligand (hormone) for binding to a fixed number of binding (receptor) sites. Detection of the unlabeled ligand occurs when the occupancy of binding sites by the unlabeled ligand is sufficient to reduce the binding of labeled ligand. A common feature of the hormone-receptor interaction is the ability of the hormone to regulate the affinity and/or the con-centration of its homologous receptor. In the present study, by exploiting the ability of human GH to regulate by negative feedback the concentration of its own receptors, we have enhanced the sensitivity of the human GH radioreceptor assay 5-fold. The ability of hormone to regulate receptor concentration and affinity affords wide opportunities to broaden the scope as well as to enhance the sensitivity of radioreceptor assays.