Pulmonary vasodilator responses to catecholamines and sympathetic nerve stimulation in the cat. Evidence that vascular β-2 adrenoreceptors are innervated

Abstract

We investigated the effects of catecholamines and sympathetic nerve stimulation in the feline pulmonary vascular bed under conditions of controlled pulmonary blood flow. Norepinephrine and nerve stimulation caused dose- and stimulus frequency-dependent increases in pulmonary vascular resistance. However, when pulmonary vascular tone was enhanced and α receptors blocked, norepinephrine and nerve stimulation caused dose- and frequency-dependent decreases in pulmonary vascular resistance. The decreases in pulmonary vascular resistance were blocked with propranolol and were of greater magnitude than were constrictor responses observed under basal conditions. Vasodilator responses to nerve stimulation were not modified by atropine. Epinephrine and isoproterenol had marked vasodilator activity in the pulmonary vascular bed when pulmonary vascular tone was elevated. When α receptors were blocked, isoproterenol and epinephrine had similar vasodilator activity, and when β receptors were blocked, epinephrine and norepinephrine had marked vasoconstrictor activity. Selective β-1 receptor antagonists had little effect on vasodilator response to isoproterenol, whereas responses to this substance were blocked by propranolol. These results suggest the presence of α- and β-2 adrenoreceptors in the feline pulmonary vascular bed and that both types of adrenergic receptors are innervated by the sympathetic nervous system.