Influence of pH on the responses of guinea-pig isolated trachea to sympathomimetic amines.

Sympathetic amines were tested on isolated trachea of guinea pig at physiological (7.4) and acid (6.6) pH. At physiological pH noradrenaline and phenylephrine relaxed the spontaneous tone of the tracheal muscle preparation; when propranolol was previously added to the organ bath solution, noradrenaline and phenylephrine didn't affect the tracheal muscle tone. Tested at acid pH (6.6), noradrenaline and phenylephrine still relaxed tracheal muscle preparations, but in the presence of propranolol these drugs increased the muscle tone. The spasmogenic effect produced by noradrenaline and phenylephrine after beta-receptor blockade by propranolol, was completely abolished by phentolamine. The present results suggest that acidosis could alter the responsiveness of both alpha- and beta-adrenoceptors in the tracheal muscle of guinea pig.