Adrenergic coronary vasoconstriction during myocardial underperfusion.

The effects of adrenergic alpha-receptor-mediated coronary vasoconstriction were examined in the presence of coronary stenosis and during experimental coronary hypoperfusion. Adrenergic coronary vasoconstriction was observed to operate even in the presence of coronary stenosis to limit oxygen delivery to the heart and increase myocardial oxygen extraction, but this vasoconstrictor effect did not result in myocardial lactate production. During constant coronary pressure perfusion the transmural distribution of alpha-receptor coronary vasoconstriction was determined with microspheres. A uniform transmural distribution of alpha-receptor-mediated vasoconstriction was observed at normal and subnormal perfusion pressures. During constant flow hypoperfusion, which permits transmural coronary steal, the left ventricular inner/outer blood flow ratio was more favorable with alpha-receptors intact than with alpha-receptors blocked. These findings indicate that alpha-receptor-mediated coronary vasoconstriction has an unexpected beneficial effect by lessening transmural steal during coronary hypoperfusion.