AJP - Lung Cellular and Molecular Physiology, Vol 269, Issue 3 293-L298, Copyright © 1995 by American Physiological Society
Alterations in pulmonary artery tone during repeated episodes of hypoxia
B. C. Yang and J. L. Mehta
Department of Medicine, University of Florida College of Medicine, Gainesville, USA.
To examine the basis of pulmonary constriction during chronic hypoxia, rat
pulmonary artery rings were precontracted and exposed to multiple episodes
of hypoxia. The first hypoxic episode resulted in a transient contraction,
followed by potent relaxation, and then a slow sustained contraction.
Repeated hypoxic exposure resulted in stronger initial contraction and
attenuated relaxation. Prolongation of the normoxic interval between
hypoxic episodes reversed the attenuation of hypoxic relaxation. Pulmonary
artery rings that were deendothelialized or treated with the nitric oxide
synthesis inhibitor N omega-nitro-L-arginine methyl ester or oxyhemoglobin
displayed only hypoxic relaxation without initial or late contractions and
no attenuation of relaxation during repeated hypoxia. Pretreatment of rings
with indomethacin or adenosine or endothelin receptor antagonists had no
effect on the hypoxia-mediated alterations. Thus repetitive exposure to
hypoxia results in an increase in initial contraction and a decrease in
relaxation of pulmonary artery rings. Frequency of hypoxic episodes and
endothelial integrity determine pulmonary tone during repeated hypoxia.
However, cyclooxygenase products, adenosine, or endothelin do not play a
role in hypoxia-mediated changes in rat pulmonary artery tone.
