A sensitive radioenzymatic assay for catechol drugs

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Abstract
This assay measures picogram quantities of catechol drugs and endogenous catecholamines in body tissues and fluids. The catechols are converted to their 3H‐O‐methyl metabolites during incubation with 3H‐S‐adenosylmethionine and the enzyme catechol‐O‐methyltransferase. The radiolabeled compounds are then separated by solvent extraction and thin‐layer chromatography. Most drugs containing the catechol structure can be radiolabeled and separated from norepinephrine and epinephrine by this technique to provide simultaneous measurement of endogenous and exogenously administered catechols. The disposition of isoproterenol in tissues and fluids of man and experimental animals is measured to illustrate the utility of this assay. The reactivity of several commonly administered catechol drugs with COMT is described and the possible implications discussed.