Demonstration of 3,4-dihydroxy[14C]benzoic acid and [14C]vanillic acid after administration of [14C]noradrenaline in the rat

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Abstract
Rats were injected with 40 μCi (±)-[1-3H]noradrenaline and 10 μCi ±-[1-14C]noradrenaline. Three fractions with a decreased 3H:14C ratio were isolated from the urine by a combined alumina adsorption-ethyl acetate extraction procedure. Two of the fractions were identified as [14C]vanillic acid and 3,4-dihydroxy[14C]benzoic acid, respectively. Vanillic acid represented between 1.5 and 3.0% of the total [14C]activity excreted within 24 h and the contribution of dihydroxybenzoic acid was 0·2-0·5%. The third fraction with a decreased 3H: 14C ratio has not been identified and represented about 2% of the total [14C]activity excreted within 24 h. After monoamine oxidase blockade with 100 mg/kg of iproniazid, the excretion of vanillic acid, 3,4-dihydroxybenzoic acid and the unknown fraction was greatly diminished. The probability that these three substances represent those metabolites arising simultaneously with the formation of tritium water from (±)-[1-3H]noradrenaline is discussed.