Coronary reactive hyperaemia and coronary dilator action of adenosine during normal respiration and hypercapnic acidosis in the dog

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Abstract
SUMMARY: 1. The effects of hypercapnic acidosis on coronary conductance, the coronary dilator effect of adenosine administered into the coronary artery and the reactive hyperaemic response after short and long periods of coronary artery occlusion were investigated in thoracotomized dogs.2. The coronary conductance was positively correlated to the arterial PCO2 and negatively correlated to the arterial pH.3. During control periods the reactive hyperaemic response increased with increasing duration of coronary artery occlusion, whereas the percentage repayment of the deficit remained unchanged.4. The reactive hyperaemic response after short periods of coronary artery occlusion (up to ten beats) was diminished during hypercapnic acidosis. This decrease may be explained on the basis of an increased tissue PO2 or a decreased relative change in tissue pH.5. The dilator effect of adenosine administered into the coronary artery was enhanced during hypercapnic acidosis.6. The reactive hyperaemic response after long periods of coronary artery occlusion (above fifteen to twenty beats) was also enhanced during hypercapnic acidosis, and may be a result of myocardial adenosine formation during coronary artery occlusion.7. The findings indicate that coronary blood flow after coronary artery occlusions may be primarily regulated by local pH changes in the coronary vessel cells. Additional dilatation after longer coronary artery occlusion may result from the release of adenosine by the hypoxic myocardium.