Acid—Base Interactions with Noradrenaline-induced Contractile Response of the Rabbit Isolated Aorta

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Abstract
The effect of acidosis and alkalosis on vascular smooth muscle contractions evoked by noradrenaline [norepinephrine] was studied. Helical strips of rabbit aorta were mounted for isometric tension recording. Acidosis (pH 7.24-6.51) was obtained by either increasing the PCO2 (hypercapnic) and/or lowering the HCO3-concentration (hypobicarbonatic). Acidosis shifted the noradrenaline concentration-response curve to the right in a competitive manner. The maximal developed tension was unchanged at pH 7.24-6.90 and decreased by 30% at pH 6.51. Alkalosis (pH 7.61-8.04) did not alter noradrenaline-evoked contractions. Hydrogen ions during acidosis (pH < 7.40) but not during alkalosis (pH > 7.40) evidently exert .alpha.-adrenoceptor blocking properties.