Effects of arachidonic acid in the rabbit pulmonary and systemic vascular beds in vivo

We studied the effects of arachidonic acid (AA) in the pulmonary and systemic circulations of rabbit under constant blood flow conditions in vivo, using a total heart bypass model. AA (100-150 micrograms/kg) injected into the pulmonary artery produced a dose-dependent increase in pulmonary arterial pressure (Ppa), without altering systemic arterial pressure (Psa). Conversely, injection of AA into the aorta reduced Psa in a dose-dependent fashion, but did not significantly alter Ppa. FPL55712, a leukotriene receptor antagonist, did not affect any of these responses to AA. Indomethacin, a cyclo-oxygenase inhibitor, totally prevented the pulmonary pressor response to intravenously administered AA and reduced the systemic depressor response to intra-arterially administered AA. The thromboxane A2 synthetase inhibitor, 7-(1-imidazolyl)heptanoic acid, totally abolished the increase in Ppa in response to intravenously administered AA, but did not alter the dose-dependent decrease in Psa in response to intra-arterially administered AA. These results suggest that in rabbits (1) AA produces pulmonary vasoconstriction and systemic vasodilation, (2) blood metabolites of AA mediate these effects and are then rapidly deactivated, and (3) AA-induced pulmonary vasoconstriction appears to be largely dependent on thromboxane A2.