Abstract
The role of enzymatic metabolism in the temperature-dependent supersensitivity to noradrenaline has been investigated at 37°C and at 26°C in isolated guinea-pig atria. In vitro monoamine oxidase (MAO) activity was found to be decreased at 26°C as compared to 37°C. However, 17–22 hr after treatment of guinea-pigs with paragyline, the degree of temperature-induced supersensitivity in isolated atria was unaltered although in vitor MAO activity was 93% inhibited at both incubation temperatures. The temperature-dependent supersensitivity of isolated atria-α methylnoradrenaline, a sympathomimetric amine not metabolized by MAO 2 was greater than that found for noradrenaline. In vitro catechol-O-methyl transferase (COMT) activity also was greater at 37°C than 26°C. In isolated atria, concentration of 3,4-dimethoxy-5-hydroxybenzoic acid which produced 33% inhibition of COMT activity in vitro, did not abolish the temperature-dependent supersensitivity to noradrenaline. However, sensitivity of isolated atria to nylidrin, a sympathomimetic amine not metabolized by COMT, is identical at the two bath temperatures. The data suggest that temperatures. The data suggets that temperature-dependent supersensitivity of isolated guinea-pig atria to sympathomimetic amines may be due to decreased COMT activity at the lower bath temperature.
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