Physiological Evaluation of Pulmonary Dilutional and Enzymatic Activity on Blood-Borne Catecholamines in Cardiocirculatory Performance

Abstract

Although the lung is a rich source of monamine oxidase and related catecholamine metabolizing and transporting enzymes, their physiologic role in cardiocirculatory regulation by affecting the properties of blood-borne sympathetic neurotransmitters is unclear. Accordingly, the present study evaluated the possibility that effects of pulmonary vasculature on systemic actions of catecholamines might be due to dilutional influences rather than to enzymatic activity. The experimental design was to compare left atrial (LA) and right atrial (RA) injections of norepinephrine (NEP) to ascertain a specific injection site effect, and upon documenting such a difference, to delineate whether the lesser RA injection effect could be accounted for by dilutional instead of enzymatic considerations. Thus, 0.2 µg/kg NEP was rapidly injected into RA or LA of 17 vagotomized open-chest intact canine preparations, and changes were observed in systemic blood pressure (BP), myocardial contractility (left ventricular dp/dt at 50 mm Hg pressure) and cutaneous vascular resistance (perfusion pressure of isolated hind-paw). TheLA bolus increased peak BP more (p < 0.01) than RA injection due to differential action (p < 0.05) on myocardial contractility, rather than by differential increase (p > 0.05) in peripheral resistance. However, when pulmonary vascular bed dilutional effects were obviated by steady state infusion (0.1 NEP µg/kg/min) into RA or LA, no