Radioreceptor Assay and Radioimmunoassay of Selected Benzodiazepines in Urine Samples From Racing Greyhounds

Radioreceptor assay and radioimmunoassay of selected benzodiazepines in urine samples from racing greyhounds. Radioreceptor assay is a quick and relatively simple analytical method which can discriminate between classes of drugs with a high degree of specificity. As it is receptors which interact and "detect" the drugs, the particular class of drugs detected is dependant on the radiolabelled ligand which is displaced from the receptor. This eliminates the need to obtain a pure preparation of one particular type of receptor which contrasts with radioimmunoassay. With this method the antibodies have to be raised against a specific drug and then purified in order that crossreactivity with drugs from other pharmacological classes does not occur. Also radioreceptor assay will only detect the pharmacologically active compounds in the biological sample. This is advantageous as only they will be acting in the body to cause an effect, so only they need to be measured. Prior to the analysis of greyhound urine samples, various aspects of the receptor assay were determined to ensure optimum results were obtained under an established set of conditions. Rat brain tissue was centrifuged in order to isolate the synaptosomal fraction containing the benzodiazepine receptors. The protein content of this fraction was estimated together with determination of the actual number of receptors and their affinity for benzodiazepines. As the brain tissue was collected in batches and stored until required, the length of time it could be kept at -2