Nitric Oxide and Prostaglandins Mediate Vasodilation to 5,6-EET in Rabbit Lung

Abstract

We have previously found that 5,6-EET (epoxyeicosatrienoic acid)(50nM) significantly dilates the vascular bed(42%) of the isolated, constantly perfused rabbit lung, which has been constricted with U46619(5–8pM). We studied the role of EDRF-NO and prostaglandins in the 5,6-EET-induced vascular relaxation. Dilation to 5,6-EET was evident only when the pulmonary vascular tone was increased. L-NNA (N^ω-nitro-L-arginine, 10⁻⁴M), an inhibitor of NO synthase(NOS); U46619(5–10pM), a thromboxane mimetic; and L-NNA+INDO(indomethacin, 10⁻⁵M), a cyclooxygenase inhibitor, all increased the pressure of pulmonary artery(PPa) from baseline, to a peak range of 28–38mmHg(32.75∐2.2), whereas INDO alone increased Ppa only by 10mmHg. L-NNA+INDO, L-NNA alone, and INDO+U46619 attenuated the 5,6-EET relaxing effect by 100%, 88% and 64.5%, respectively. In the presence of L-NNA and 5,6-EET, SNAP(S-nitroso-N-acetyl-D, L-penicillamine, 10⁻⁶M), a NO donor, reduced Ppa by 75%. We conclude that the mechanism of vasodilation to 5,6-EET in the rabbit pulmonary circulation is via both EDRF-NO and PG pathways and that the vasodilation is largely EDRF-NO dependent. (Supported by National Institutes of Health PO1 HL43023).