Physiol. Res. 49: 549-506, 2000

MINIREVIEW

Altered Pulmonary Vasoreactivity in the Chronically Hypoxic Lung

L. A. Shimoda, J. S. K. Sham, J. T. Sylvester

Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, School of Medicine Baltimore, Maryland, USA

Received February 29, 2000
Accepted April 3, 2000


Summary
Prolonged exposure to alveolar hypoxia induces physiological changes in the pulmonary vasculature that result in the development of pulmonary hypertension. A hallmark of hypoxic pulmonary hypertension is an increase in vasomotor tone. In vivo, pulmonary arterial smooth muscle cell contraction is influenced by vasoconstrictor and vasodilator factors secreted from the endothelium, lung parenchyma and in the circulation. During chronic hypoxia, production of vasoconstrictors such as endothelin-1and angiotensin II is enhanced locally in the lung, while synthesis of vasodilators may be reduced. Altered reactivity to these vasoactive agonists is another physiological consequence of chronic exposure to hypoxia. Enhanced contraction in response to endothelin-1 and angiotensin II, as well as depressed vasodilation in response to endothelium-derived vasodilators, has been documented in models of hypoxic pulmonary hypertension. Chronic hypoxia may also have direct effects on pulmonary vascular smooth muscle cells, modulating receptor population, ion channel activity or signal transduction pathways. Following prolonged hypoxic exposure, pulmonary vascular smooth muscle exhibits alterations in K+ current, membrane depolarization, elevation in resting cytosolic calcium and changes in signal transduction pathways. These changes in the electrophysiological parameters of pulmonary vascular smooth muscle cells are likely associated with an increase in basal tone. Thus, hypoxia-induced modifications in pulmonary arterial myocyte function, changes in synthesis of vasoactive factors and altered vasoresponsiveness to these agents may shift the environment in the lung to one of contraction instead of relaxation, resulting in increased pulmonary vascular resistance and elevated pulmonary arterial pressure.


Key words
Contraction · Endothelin-1 · Angiotensin II · Nitric oxide · Membrane potential · Pulmonary hypertension

Reprint requests
Larissa A. Shimoda, Ph.D., Division of Pulmonary and Critical Care Medicine, 5501 Hopkins Bayview Circle, Baltimore, MD 21224, USA, FAX (410)-550-2612, E-mail: shimodal@welch.jhu.edu


© 2000 by the Institute of Physiology, Czech Academy of Sciences