Nitric oxide and nitroglycerine reversal of pulmonary
vasoconstriction induced by alpha adrenoceptor activation during
exercise.
Koizumi, Tomonobu, Casilda I. Hermo, Lars J. Bjertnaes, Mukul
Banerjee, John H. Newman, Keishi Kubo.
Center for Lung Research, Vanderbilt University School of Medicine
and Department of Physiology, Meharry Medical College, Nashville,
Tennessee
APStracts 2:0433H, 1995.
We have previously shown in sheep that pulmonary vascular resistance
decreases rapidly after the onset of constant exercise, followed by a
slower and smaller second vasodilation. The second phase is partly
regulated by alpha- and beta-adrenoceptor activation. We examined the
effect of inhaled nitric oxide (NO) 40 ppm, and i.v. nitroglycerine,
on beta adrenergic blockade-induced pulmonary vasoconstriction during
exercise. In paired studies, we exercised 8 sheep at a constant rate
of 4 mph for 4 min on a treadmill and measured the hemodynamic
response during beta blockade (propranolol 1 mg, iv) with and without
40 ppm inhaled NO or continuous infusion of nitroglycerine (3.2-4.0
ug/kg/ min). Beta blockade resulted in a higher pulmonary vascular
resistance during steady-state exercise (40-240 sec) than in the
unblocked state; reduction in pulmonary vascular resistance during
the second phase of exercise was smaller with beta blockade (13-16%)
than with control exercise (26-30%). Inhaled NO and nitroglycerine
reversed the beta blockade-related pulmonary vasoconstriction to the
levels of control exercise. Inhaled NO and iv nitroglycerine also
reversed the pulmonary vasoconstriction produced by iv phenylephrine
at rest. We conclude that exogenous NO, delivered by gas inhalation
or via nitroso compounds opposes and fully reverses alpha receptor
-activated pulmonary vasoconstriction during exercise in sheep.
Received 22 May 1995; accepted in final form 24 August 1995.
APS Manuscript Number H476-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 31 October 95