Radioreceptor assays substances measured

In order to demonstrate specificity, investigators have quantified samples using the radioreceptor assay and some other method of analysis, on the premise that if the values obtained are similar, then the radioreceptor assay is appropriate under the conditions employed. For example, the serum concentration of neuroleptics can be determined using a radioreceptor assay based on the dopamine receptor binding procedure (Creese and Snyder, 1977). To demonstrate the specificity of this assay, some samples were analyzed using both the radioreceptor assay and a radioimmunoassay (Table 3). The results obtained were virtually identical, indicating that the radioreceptor assay was measuring the same substance as that detected by radioimmunoassay. 

Radioreceptor assay is a well established technique being increasingly utilized in both research and clinical medicine (1)(2). Details of this technique have been described in many publications, and for our purposes it is sufficient to say that these assays involve a competitive binding reaction between two major components, the binding material (antibody, binding protein, or membrane receptors) and the substances to be measured (hormones, drugs, enzymes, etc.). 

One of the chief advantages of radioreceptor assays over most other analytical procedures is that, in many cases, very little or no extraction of the sample is necessary prior to analysis. Thus, to measure GABA in CSF, small portions of untreated spinal fluid are placed directly into the receptor binding assay tubes since other CSF substances do not appreciably... 

Radioreceptor assays for neurotransmitters and drugs have been used to measure a variety of substances in a number of different tissues and fluids (Table 4). 

The studies on the insulin receptor of human lymphocytes led to the development of a sensitive radioreceptor assay which complements the radioimmunoassay in measuring minute quantities of substances in plasma with insulin bioactivity. Using this technique clinically, a patient with a primary defect in insulin receptor deficiency was reported . In the same study, acquired and reversible receptor deficiency was also observed in obese patients . In the obese-hyperglycemic mutant mouse, insulin-resistance appears to correlate directly with an irreversible deficiency in insulin receptor activity on the adipocyte and hepatocyte plasma membranes. Cuatrecasas and his co-workers, on the other hand, reported the same number of insulin-binding sites in adipocytes from obese and insulin-resistant rats as were present in those from normal animals They proposed that the metabolic defect in these animals resides in the coupling of the signals of the insulin-receptor complex to glucose transport. 

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