The dependence of the effects of i.cor. administered adenosine and of coronary conductance on the arterial pH, pCO 2 and buffer capacity in dogs.

Abstract

Coronary conductance and the coronary dilatory action of adenosine, injected into the left coronary artery, were investigated at different arterial pH andpCO2 in intact anaesthetized dogs. Four groups of experiments were carried out: Experiments with slow i.v. infusion 1. of 0.1 N HCl, 2. of 5% NaHCO3, 3. of 1 M THAM and 4. of 0.1 N HCl following a preceding infusion of THAM. The following results were obtained: 1. The vasodilatory effect of an intracoronarily injected dose of 1–2μg/kg adenosine showed a highly significant negative correlation with the arterial pH and a significant positive correlation with the arterialpCO2 in those groups, where the changes in arterial pH andpCO2 were accompanied by changes in the extracellular buffer capacity (infusions of HCl, NaHCO3 and THAM). 2. Coronary conductance showed a significant negative correlation to the arterial pH in those experiments where changes in arterial pH were accompanied by reciprocal changes in arterialpCO2 (infusions with HCl, THAM and HCl after THAM). Even on exclusion of the influence of concomitant changes in heart rate on coronary conductance by a partial correlation analysis the correlation between coronary conductance and arterial pH remained highly significant in the experiments with HCl and THAM infusions. 3. The results obtained with adenosine were discussed with respect to the theory of a “propagated metabolic acidosis” as an underlying mechanism of the coronary dilatory action of adenosine. An importance of the coronary smooth muscle intracellular pH as a determining factor of coronary vascular tonus was suggested.