| Abstract: | The effect of norepinephrine (NE) on reactive myocardial hyperemia (RH) after a brief (20 sec) flow arrest was studied in 9 closed-chest anesthetized dogs. NE infusion into the left ventricle resulted in the increase of RH peak during coronary flow and the elevation of the left ventricular pressure and its first derivative. The increased coronary dilatation may be explained by the activation of beta 1-adrenergic myocardial receptors. RH peak decreased later, with the coronary flow, left ventricular pressure and its first derivative returning to the control level. This RH decrease can be explained by the activation of alpha-adrenergic receptors of the coronary vessels and the competition between alpha-receptors for vasoconstriction and metabolic vasodilatation. |
