Changes in Coronary Venous Inosine Concentration and Myocardial Wall Thickening during Regional Ischemia in the Pig

Correlations between local mechanical and metabolic events were studied during a partial decrease in flow in the left anterior descending coronary artery in 14 open-chest pigs. A decrease in flow to 28% (19-39%) of the control value was achieved with an adjustable screw clamp. A flow probe was placed around the artery. Blood samples were taken from the regional anterior coronary vein and the femoral artery. Myocardial wall thickening was measured with a harpoon type of mercury strain gauge. During ischemia, systolic myocardial wall thickening decreased to 44.5 ± 5.1% ( SE ) of its control value ( P < 0.001). The mean concentrations of plasma potassium and whole blood inosine, hypoxanthine, and lactate in three serial 2-minute samples obtained during a 6-minute control period were compared with those obtained during a 6-minute period of partial occlusion. During ischemia, venous inosine concentration increased from 10.9 ± 0.7 µ M to 18.5 ± 1.8 µM ( P < 0.005), venous hypoxanthine concentration increased from 28.5 ± 1.4 µ M to 33.0 ± 1.5 µ M ( P < 0.005), venous potassium concentration increased from 3.77 ± 0.10 m M to 4.08 ± 0.13 m M ( P < 0.001), and venous lactate concentration increased from 1.04 ± 0.19 m M to 1.52 ± 0.17 m M ( P < 0.001). The arterial level of potassium increased very little. The arterial concentration of the other compounds did not change significantly during the 6-minute period of ischemia. Myocardial lactate extraction changed from a control value of 42.6 ± 6.7% to -4.6 = 12.5% ( P < 0.05). A negative correlation ( r s = -0.79, P < 0.01) was observed between venous inosine concentration and myocardial wall thickening (percent of control) during ischemia. This study indicates that the local venous inosine concentration is a sensitive indicator of regional myocardial ischemia in the pig.