THE UPTAKE KINETICS AND METABOLISM OF EXTRANEURONAL NORADRENALINE IN GUINEA‐PIG TRACHEA AS STUDIED WITH QUANTITATIVE FLUORESCENCE MICROPHOTOMETRY

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Abstract
1 Extraneuronal uptake of noradrenaline and α-methylnoradrenaline into single cells of guinea-pig tracheal smooth muscle have been studied by means of quantitative fluorescence microphotometry. 2 Fluorescence brightness due to accumulation of α-methylnoradrenaline was dose-dependent and was increased by the catechol-O-methyltransferase inhibitor drugs, tropolone or β-thujaplicin (200 μM) but not by 3,4-dimethoxy-5-hydroxybenzoic acid (200 μM). 3 Fluorescence brightness due to accumulation of noradrenaline was increased if animals were pretreated with the monoamine oxidase inhibitor drug, nialamide. 4 The study suggests that metabolism of amines by catechol-O-methyltransferase and monoamine oxidase can occur subsequent to extraneuronal uptake in guinea-pig tracheal smooth muscle. 5 The uptake of noradrenaline into tracheal smooth muscle was concentration-dependent, saturable, and had a Km of 156 μM.