Influence of aspirin and indomethacin on variability of alveolar hypoxic vasoconstriction

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Abstract
Alveolar hypoxia induces pulmonary vasoconstriction but the strength of alveolar hypoxic vasoconstriction (AHV) is variable even within the same species. The influence of aspirin and indomethacin, cyclooxygenase inhibitors, was examined in 2 groups of dogs, those with weak AHV and those with vigorous AHV. A double-lumen endotracheal tube allowed ventilation of 1 lung with N as an alveolar hypoxic stimulus and ventilation of the other lung with O2 to maintain systemic oxygenation. Perfusion to each lung was measured with Xe-133 and external counters. In weak reactors both aspirin and indomethacin induced 4-fold enhancement of AHV (P < 0.01), while no significant influence on vigorous reactors was noted. Cyclo-oxygenase inhibitors also produced enhanced reactivity in the isolated lung to alveolar hypoxia and prostaglandin F2.alpha. but not to angiotensin II and norepinephrine. Aspirin-enhanced AHV in the isolated lung could not be diminished with blockade of angiotensin II receptors or of .alpha. receptors. Weak AHV in intact or isolated dog lung may be due to an excess of a prostaglandin or prostacyclin vasodilator.