EDHF function in the ductus arteriosus: evidence against involvement of epoxyeicosatrienoic acids and 12S-hydroxyeicosatetraenoic acid

We have previously shown (Ref. 2) that endothelium-derived hyperpolarizing factor (EDHF) becomes functional in the fetal ductus arteriosus on removal of nitric oxide and carbon monoxide. From this, it was proposed that EDHF originates from a cytochrome P-450 (CYP450)-catalyzed reaction being inhibited by the two agents. Here, we have examined in the mouse ductus whether EDHF can be identified as an arachidonic acid product of a CYP450 epoxygenase and allied pathways. We did not detect transcripts of the mouse CYP2C subfamily in vessel, while CYP2J subfamily transcripts were expressed with CYP2J6 and CYP2J9. These CYP2J hemoproteins were also detected in the ductus by immunofluorescence microscopy, being colocalized with the endoplasmic reticulum in both endothelial and muscle cells. Distinct CYP450 transcripts were also detected and were responsible for omega-hydroxylation (CYP4A31) and 12R-hydroxylation (CYP4B1). Mass spectrometric analysis showed formation of epoxyeicosatrienoic acids (EETs) in the intact ductus, with 11,12- and 14,15-EETs being more prominent than 5,6- and 8,9-EETs. However, their yield did not increase with nitric oxide/carbon monoxide suppression, nor did it abate with endothelium removal. No evidence was obtained for formation of 12R-hydroxyeicosatrienoic acid and omega-hydroxylation products. 2S-hydroxyeicosatetraenoic acid was instead detected, and, contrary to data implicating this compound as an alternative EDHF, its suppression with baicalein did not modify the EDHF-mediated relaxation to bradykinin. We conclude that none of the more common CYP450-linked arachidonic acid metabolites appears to qualify as EDHF in mouse ductus. We speculate that some novel eicosanoid or a totally unrelated compound requiring CYP450 for its synthesis accounts for EDHF in this vessel.