MYOCARDIAL SUBSTRATE UPTAKE IN LAMBS WITH AND WITHOUT AORTOPULMONARY SHUNTS DURING STRENUOUS EXERCISE

Increased myocardial fatty acid uptake during acute exercise could adv ersely affect myocardial O2 consumption in lambs with left-to-right sh unts, which would be unfavorable in view of their decreased coronary b lood flow reserve. Therefore, we studied myocardial substrate uptake ( glucose, lactate, pyruvate, free fatty acids, triglycerides, beta-hydr oxybutyrate, and acetoacetate) in 10 7-wk-old lambs with an aortopulmo nary left-to-right shunt [61 +/- 3% (SE) of left ventricular output] a nd 9 control lambs during strenuous treadmill exercise. The hemodynami c reaction to exercise was similar in shunt and control lambs. The per ipheral metabolic response to exercise was also similar in the two gro ups: glucose, free fatty acids, and, most prominently, lactate concent rations increased. Myocardial O2 consumption increased but less in shu nt than in control lambs because of a smaller increase in heart rate. In both groups myocardial lactate uptake increased substantially at th e cost of other substrates, providing the heart with 40% of its oxidat ive metabolism. Fatty acid uptake was not different between the two gr oups. In conclusion, our data reveal no essential differences in myoca rdial substrate uptake between shunt and control lambs during a substa ntial circulatory load.