Coronary blood flow regulation in the prediabetic metabolic syndrome

This study tested whether the pre-diabetic metabolic syndrome impairs coronary blood flow control sufficiently to alter the balance between coronary blood flow and myocardial metabolism. Experiments were conducted in dogs instrumented with catheters in the aorta, coronary sinus, and left ventricle and with flow transducers around the circumflex coronary artery and aorta. Coronary blood flow, myocardial oxygen consumption (MVO₂), cardiac output, aortic pressure, left ventricular pressure and heart rate were measured at rest and during treadmill exercise in normal, control and high fat fed dogs. High fat feeding for ∼ six weeks increased body weight 15%, increased aortic blood pressure 10%, and induced insulin resistance. Fasting plasma insulin levels were increased 2.4-fold while plasma glucose concentration was unchanged relative to controls (5.0 ± 0.3 mM). The cardiac index increased with exercise but was not altered by high fat feeding. The metabolic syndrome reduced the slope of the relationship between coronary blood flow and MVO₂ (P < 0.0001) and decreased coronary venous PO₂ at a given level of MVO₂ (P < 0.05). These findings indicate that the metabolic syndrome impairs the balance between myocardial oxygen delivery and metabolism by tonically vasoconstricting the coronary circulation.