Neural, humoral, and metabolic control of coronary vascular resistance during exercise

Neural, humoral, and metabolic effects on coronary vascular resistance were examined during exercise in conscious dogs, chronically instrumented for the measurement of aortic pressure, heart rate, and left circumflex coronary blood flow. Exercise significantly decreased coronary vascular resistance (CVR) in intact (INT) group, in which CVR was controlled by neural, humoral, and metabolic factors. In cardiac denervated (CD) group with pretreatment of alpha blocker (phentolamine, 2 mg/kg), in which CVR was controlled only by metabolic factor, exercise significantly decreased CVR. To eliminate metabolic effect on CVR, CVR was normalized by the product of CVR and double product (DP = mean aortic pressure x heart rate). CVR.DP did not change throughout the exercise in dogs with CD with alpha blocker. Thus, metabolic effect on CVR during exercise can be excluded by the product of CVR and DP. This calculation was applied to INT group with alpha blocker and CD group without blockers. The 12 km/h exercise significantly increased CVR.DP from 4.1 +/- 0.3 x 10(4) to 6.4 +/- 0.9 x 10(4) in INT group with alpha blocker, in which CVR was controlled only by neural factor, and from 2.8 +/- 0.2 x 10(4) to 4.5 +/- 0.5 x 10(4) in CD group, in which CVR was controlled only by humoral factor. These data suggest that 1) neural and humoral coronary vasoconstriction occurs during exercise, 2) neural and humoral vasoconstriction is overwhelmed by metabolic vasodilation, and 3) CVR.DP is a beneficial calculation for excluding metabolic effect on CVR during exercise.