Analysis of coronary vascular beta receptors in situ.

Observations were conducted in the isolated potassium-arrested dog heart to determine the direct vasodilator effects of adrenergic agonists and antagonists on the coronaryvascular beta receptors, independent of cardiac inotropic and chronotropic influences. Practocol (a selective beta-1-receptor antagonist) blocked coronary vasodilation activated by isoproternol (a combined beta-1-and beta-2-receptor agonist) only at the very high dose of 10-minus 3 M, whereas propranolol (a combined beta-1- and beta-2-receptor antagonist) blocked coronary vasodilation at 10-minus 7 to 10-minus 5 M. Salbutamol (a selective beta-2-receptor agonist) was one-eighth as potent as isoproterenol in producing coronary vasodilation. The potency ratio (1/8) is similiar to valuesreported for other beta receptors classified as type 2. It is concluded that the coronary vasodilator beta receptors are type 2, similiar to those found in peripheral bloodvessels.