ACUTE MYOCARDIAL-ISCHEMIA CAUSES A TRANSMURAL GRADIENT IN GLUCOSE EXTRACTION BUT NOT GLUCOSE-UPTAKE

We assessed the relationship between myocardial glucose metabolism and blood flow during ischemia in eight open-chest swine. Coronary flow was controlled by an extracorporeal perfusion circuit. Left anterior descending coronary arterial (LAD) flow was reduced by 60%, while left circumflex flow was normally perfused. The rate of glucose uptake (R(g)) was measured with a coronary infusion of 2-deoxy-D-[C-14]glucose and myocardial blood flow with radiolabeled microspheres. Myocardial biopsies were taken after 50 min of ischemia. Regional arterial-venous glucose difference was calculated as R(g) per myocardial blood flow. Subendocardial blood flow decreased from 1.27 +/- 0.19 to 0.25 +/- 0.11 ml.g-1.min-1 (P < 0.0001). The subendocardial arterial-venous glucose difference was greater in the LAD bed (1.38 +/- 0.35-mu-mol/ml) than the left circumflex coronary arterial perfusion bed (0.10 +/- 03; P < 0.001); however, there was no statistically significant difference in the rate of glucose uptake between the two beds. Subendocardial glycogen concentration in the LAD perfusion bed was reduced to 26% of circumflex bed values. In conclusion, acute ischemia stimulated a dramatic increase in glucose extraction; however, this did not compensate for the decrease in blood flow, and thus the rate of glucose uptake did not increase significantly. The high rate of glycolysis is primarily supported by accelerated net glycogen breakdown rather than increased glucose uptake.