Metabolism of isoprenaline in dog and man

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Abstract
1 The metabolism of isoprenaline has been studied in man and dog following intravenous and oral or intra-duodenal administration. 2 Intravenous isoprenaline was excreted largely unchanged in urine in both species. Only one-third of the radioactivity in urine was in the form of the O-methyl metabolite. 3 After oral doses in man or intraduodenal doses in dogs, plasma radioactivity was almost entirely as conjugated isoprenaline and this metabolite accounted for more than 80% of radioactivity in urine. 4 Catechol-O-methyl transferase may be less important than Uptake2 in limiting the pharmacological action of isoprenaline. 5 Pharmacological response (heart-rate increase) was related to plasma concentration of isoprenaline only after rapid intravenous injections. In dogs, following prolonged infusion or intraduodenal doses, heart rate returned to base-line values when plasma concentrations of isoprenaline were high.