CANINE MYOCARDIAL ADENOSINE AND LACTATE PRODUCTION, OXYGEN-CONSUMPTION, AND CORONARY BLOOD-FLOW DURING STELLATE GANGLIA STIMULATION

The vasodilator adenosine is produced continuously by the normal dog myocardium. However, the relation of adenosine production to increased cardiac metabolism requires clarification. This study tested the hypothesis that increased myocardial O2 demand promotes increased adenosine production to match coronary blood flow (CBF) to metabolic requirements. Increased adenosine production, therefore, should correlate with increased CBF and myocardial oxygen consumption (MVO2). Graded changes in CBF were induced through bilateral stellate ganglia stimulation (SGS) in open-chest dogs. Left CBF, MVO2, and the adenosine and lactate contents of pericardial infusate (Krebs-Henseleit solution) were measured. Pericardial infusate was placed in contact with the epicardium through a cannula introduced through the otherwise intact pericardium. Left ventricular tissue samples frozen in situ also were obtained after the infusate was withdrawn and analyzed for adenosine and lactate. The correlation of infusate adenosine concentration with CBF was found to be significant, as was the correlation of adenosine concentration with MVO2. Tissue adenosine levels increased significantly with SGS and were reflected in significant increases in pericardial infusate adenosine content. Adenosine concentration of the infusate was also measured after contact for different times with the epicardium (0.5-18 minutes) and found to increase continually throughout the times studied, but it did not reach equilibrium with tissue adenosine levels. Loss of adenosine from the infusate also was found to be rapid, indicating a high turnover of pericardial fluid adenosine. Results support adenosine as a coupler of myocardial metabolism to CBF and the use of pericardial infusate adenosine content as an index of tissue adenosine production.