Adrenic acid metabolites as endogenous endothelium-derived and zona glomerulosa-derived hyperpolarizing factors.

Adrenic acid (docosatetraenoic acid), an abundant fatty acid in the adrenal gland, is identical to arachidonic acid except for 2 additional carbons on the carboxyl end. Adrenic acid is metabolized by cyclooxygenases, cytochrome P450s, and lipoxygenases; however, little is known regarding the role of adrenic acid and its metabolites in vascular tone. Because of its abundance in the adrenal gland, we investigated the role of adrenic acid in vascular tone of bovine adrenal cortical arteries and its metabolism by bovine adrenal zona glomerulosa cells. In adrenal cortical arteries, adrenic acid caused concentration-dependent relaxations, which were inhibited by the epoxyeicosatrienoic acid antagonist 14,15-epoxyeicosa-5(Z)-enoic acid and the cytochrome P450 inhibitor SKF-525A. The large-conductance calcium-activated potassium channel blocker iberiotoxin or removal of the endothelium abolished these relaxations. Reverse-phase high-pressure liquid chromatography and liquid chromatography/mass spectrometry isolated and identified numerous adrenic acid metabolites from zona glomerulosa cells, including dihomo-epoxyeicosatrienoic acids and dihomo-prostaglandins. In denuded adrenal cortical arteries, adrenic acid caused concentration-dependent relaxations in the presence of zona glomerulosa cells but not in their absence. These relaxations were inhibited by SKF-525A, 14,15-epoxyeicosa-5(Z)-enoic acid, and iberiotoxin. Dihomo-16,17-epoxyeicosatrienoic acid caused concentration-dependent relaxations of adrenal cortical arteries, which were inhibited by 14,15-epoxyeicosa-5(Z)-enoic acid and high potassium. Our results suggest that adrenic acid relaxations of bovine adrenal cortical arteries are mediated by endothelial and zona glomerulosa cell cytochrome P450 metabolites. Thus, adrenic acid metabolites could function as endogenous endothelium-derived and zona glomerulosa-derived hyperpolarizing factors in the adrenal cortex and contribute to the regulation of adrenal blood flow.