Hypoxia induces the release of a pulmonary-selective, Ca2+-sensitising, vasoconstrictor from the perfused rat lung

OBJECTIVE: Sustained hypoxic pulmonary vasoconstriction is dependent upon the presence of an intact endothelium, strongly suggesting that an endothelium-derived constrictor factor is involved in this response. In the present study we have attempted to determine whether hypoxia induces the release of a vasoconstrictor(s) from the lung, and whether this vasoconstrictor shares mechanistic features with the hypoxic constrictor response. METHODS: The salt-perfused rat lung, coupled with a simple solid-phase extraction process, and a rat intrapulmonary artery functional bioassay were utilised in this study. RESULTS: Hypoxic, but not normoxic, perfusion of the isolated lung of the rat induced the release of a vasoconstrictor(s) which appeared to be selective for pulmonary over mesenteric arteries of the rat. The vasoconstriction observed was unaffected by inhibition of voltage-gated Ca(2+) channels, and was not associated with a rise in intracellular [Ca(2+)], suggesting Ca(2+)-sensitisation of the contractile apparatus. The vasoconstriction was also unaffected by the protein kinase C (PKC) inhibitor Ro-31-8220, or the endothelin-1 antagonists BQ123/BQ788 but was markedly potentiated in the presence of prostaglandin F(2alpha). CONCLUSION: We conclude that hypoxic perfusion of the rat lung results in the release of a vasoconstrictor(s) which shares some of the facets of the sustained hypoxic constriction of isolated intrapulmonary arteries of the rat, since it involves PKC-independent Ca(2+) sensitisation, is independent of voltage-gated Ca(2+) entry, and is potentiated by the presence of preconstriction.