Influence of alpha- and beta-sympathetic blockade on hypoxic sensitivity of the coronaries

The effect of 2 types of adrenergic blockade on the capacity of the coronaries for hypoxic dilatation was studied in open chest dogs under chloralose anesthesia. Reactive hyperemia following the temporary occlusion of the left coronary artery and the vasodilatation elicited by general arterial hypoxia served to determine the range of coronary adaptation. beta-adrenergic blockade induced by propranolol (0.3 mg/Kg i.v. or 0.05 mg/Kg intracoronarially) failed to reduce the range of hypoxic dilatation. On the other hand, the alpha-blocking agent phentolamine (0.45 mg/Kg i.v. or 0.15 mg/Kg i.c.), in association with a decrease of the vascular tone, significantly limited the coronary adaptation to hypoxia.