Effect of pH on norepinephrine-induced contractions of isolated arterial smooth muscle

Isolated muscle strips, spirally cut from the rat aorta, were suspended in various Krebs solutions which simulated conditions of respiratory and metabolic acidosis. The contraction of these strips following exposure to norepinephrine was found to be maximal in states of relative alkalosis and minimal in states of acidosis. In ‘respiratory acidosis,’ the inhibition of the norepinephrine-induced contraction averaged 43%. In a comparable ‘metabolic acidosis,’ the inhibition was markedly less but still averaged 26%. In a more severe ‘metabolic acidosis,’ the inhibition was 32% when compared to a solution with a ‘normal’ pH. In solutions with a ‘normal’ pH, the combination of a high CO2 tension and a high bicarbonate concentration will also inhibit a norepinephrine-induced contraction when compared to a solution of the same pH with the combination of a low CO2 tension and a low bicarbonate concentration. The observations suggest that correction of the acidosis which often accompanies shock should make the shock more amenable to treatment.