5,6-EPOXYEICOSATRIENOIC ACID REDUCES INCREASES IN PULMONARY VASCULAR-RESISTANCE IN THE DOG

We recently reported that canine pulmonary microsomes metabolize arach idonic acid to all four regioisomeric epoxyeicosatrienoic acids (EET). 5,6-EET dilates blood vessels in several nonpulmonary vascular beds, often in a cyclooxygenase-dependent manner. The present study was desi gned to determine whether 5,6-EET can decrease pulmonary vascular resi stance (PVR) in the intact pulmonary circulation. In isolated canine l ungs perfused with physiological salt solution, a constant infusion of U-46619 (3.28 +/- 0.99 nmol/min) increased PVR 62.1 +/- 4.5%. Adminis tration of 5,6-EET (10(-5) M) into the perfusate reduced the U-46619-m ediated increase in PVR by 23.6 +/- 6.1%. These effects of U-46619 and 5,6-EET were limited to changes in resistance solely in the pulmonary venous segment. In contrast, venous as well as arterial segmental res istances were increased in 5-hydroxytryptamine (5-HT)-treated lungs. H owever, in the latter instance, 5,6-EET reduced arterial but not venou s segmental resistance. 5,6-EET increased pulmonary PGI(2) synthesis f rom 70.5 +/- 18.4 to 675.9 +/- 125.4 ng/min. In the presence of indome thacin (10(-4) M), 5,6-EET did not increase PGI2 synthesis nor did it decrease U-46619- or 5-MT-mediated increases in PVR. In canine intrapu lmonary vessels, 5,6-EET decreased active tension in veins contracted with U-46619. 5,6-EET decreased active tension in arteries but not vei ns contracted with 5-HT, consistent with results in the perfused lungs . These results demonstrate that 5,6-EET is a vasodilator in the intac t pulmonary circulation. Its dilator activity depends on the constrict or agent present, the segmental resistance, and cyclooxygenase activit y.