Effect of hypothermia on β1‐adrenoceptor‐mediated relaxation of pig bronchus

Abstract

The relaxant potencies of (±)‐isoprenaline and of (−)‐noradrenaline (NA) in the pig isolated bronchus were increased 5.4 and 3.1 fold respectively by lowering the organ bath temperature from 37°C to 27°C, whereas the potencies of the non‐catecholamine β‐adrenoceptor agonists fenoterol and orciprenaline were not significantly changed. At 37°C, the catechol‐O‐methyl transferase (COMT) inhibitor U‐0521 (30 μm), caused a 7.2 fold increase in the potency of isoprenaline but had no effect on the potency of fenoterol. At 27°C the potency of isoprenaline was similar in the absence or presence of U‐0521 (30 μm). Furthermore, in bronchi where extraneuronal uptake was inhibited by phenoxybenzamine, the potency of NA was not significantly altered by reducing bathing temperature from 37°C to 27°C. These results suggest that the hypothermic potentiation of isoprenaline in pig bronchus resulted from inhibition of COMT or of access to COMT, rather than from sensitization of β1‐adrenoceptors. 1983 British Pharmacological Society