Hypoxic contraction of isolated rat pulmonary artery

The effects of hypoxia in precontracted rat pulmonary artery rings with and without endothelium was studied. Hypoxia (30 mmHg) produced a contraction (hypoxic pulmonary vasoconstriction, HPV). Removal of endothelium abolished the HPV. The HPV was reproducible. The amplitude of HPV was similar to arteries equilibrated with 100% O2 and room air. L-NNA markedly inhibited the HPV whereas indomethacin was ineffective. HPV was inhibited by caffeine, but not inhibited by nifedipine. It would be concluded that HPV in isolated rat pulmonary arteries is dependent on the endothelium and the mechanisms involved may be inhibition of basal NO production.