Myocardial adenosine and coronary resistance during increased cardiac performance.
The relation between myocardial adenosine content and coronary vascular resistance was studied in the open-chest dog. Cardiac performance was increased by aortic constriction or by intravenous infusion of isoproterenol. Coronary blood flow was measured by the microsphere tracer technique. In control animals, adenosine content and coronary vascular resistance were 0.22 +/- 0.03 nmol/g and 1.9 +/- 0.11 mmHg . ml-1 . min . 100 g, respectively. A range of myocardial oxygen consumptions of 5.3-24 ml O2 . min-1 . 100 g-1 was elicited. This was associated with a range of coronary blood flows of 33-166 ml . min-1 . 100 g-1. There was a significant negative correlation between coronary vascular resistance and the log of the myocardial adenosine content (r = 0.77). There was no transmural gradient in adenosine content in the control and aortic-constricted groups, but there was a significant adenosine gradient in the isoproterenol-infused group in which coronary input pressure was decreased. The hearts were not ischemic, as indicated by low myocardial lactate contents and a stable coronary sinus blood pH. These results provide support for a role of adenosine in the local control of the coronary circulation during increased cardiac performance.