HET0016 inhibits epoxyeicosatrienoic acid‐induced pulmonary vasoconstriction by an ω‐hydroxylase‐independent mechanism

Recently, endogenous epoxyeicosatrienoic acids (EETs) were reported to be required for full expression of hypoxic vasoconstriction in a model of pulmonary hypertension. Previously, a cytochrome P450 (CYP) ω‐hydroxylase enzyme, CYP4A, was identified in the rabbit pulmonary artery (PA). The major arachidonic acid (AA) metabolite of CYP4A, 20‐HETE, is a pulmonary vasodilator. Endogenous 20‐HETE blunts hypoxia‐ and agonist‐induced pulmonary vasoconstriction. Thus, 20‐HETE may blunt EET‐induced pulmonary vasoconstriction. To test this hypothesis, we determined whether inhibition of ω‐hydroxylase activity would augment 5,6‐EET‐induced PA constriction. PA (1–3 mm od) rings were suspended from force displacement transducers in physiological salt solution gassed with 95% O 2 , 5% CO 2 . HET0016, a selective inhibitor of CYP4A activity, reduced 5,6‐EET‐induced PA contraction at 1–10 μM (P<0.05), whereas a non‐selective CYP inhibitor, 17‐ODYA (10 μM), did not. HET0016 (10 μM) did not inhibit PGF 2α ‐ or 5‐HT‐ induced PA contractions but did inhibit AA‐ (5 μM) induced contractions. Since 5,6‐EET and AA, but not PGF 2α and 5‐HT ‐induced PA contractions require cyclooxygenase activity, these results suggest that HET0016 (1–10 μM) inhibits 5,6‐EET‐induced contractions, not by inhibiting ω‐hydroxylase enzyme activity, but by inhibiting cyclooxygenase activity, an often overlooked property HET0016. Support: NIH HL‐64180.