Autonomic Regulation of the Pulmonary Circulation

Responses to vagal stimulation, acetylcho-line, catecholamines, and sympathetic nerve stimulation were investigated in the feline pulmonary vascular bed under conditions of controlled pulmonary blood flow and constant left atrial pressure. Results of these studies suggest that, in the cat, the vagus is composed of efferent fibers from both the sympathetic and parasympathetic systems. The data also suggest that the feline pulmonary vascular bed is functionally innervated by cholinergic nerves, and that vagal stimulation dilates the pulmonary vascular bed by releasing acetylcholine, which acts on muscarinic receptors in pulmonary vessels, α and ß2-adrenoceptors appear to be present in the feline pulmonary vascular bed, and both types of adrenergic receptors are innervated by the sympathetic nervous system. Selective α1- and α2-receptor agonists produce pulmonary vasoconstrictor responses, suggesting the presence of both α1- and α2-receptor subtypes in the feline pulmonary vascular bed. The pulmonary vascular response to nor-epinephrine, dopamine, and dobutamine is the algebraic summation of activation of α- and ß-adrenoceptors. Dopamine possesses greater α-(vasoconstrictor) activity when compared to dobutamine, whereas dobutamine has greater ß-(vasodilator) activity.