Nitric Oxide Attenuates the Release of Endothelium-Derived Hyperpolarizing Factor

TLDR

The role of the endothelium‑derived hyperpolarizing factor (EDHF) in physiological vasodilation remains unclear because its effect is only detectable after inhibition of nitric oxide synthase and cyclooxygenase. This study investigated whether nitric oxide feedback inhibits EDHF production in isolated perfused arterial segments. Using NO donors under combined NO synthase and cyclooxygenase blockade, the authors showed that NO attenuates EDHF‑mediated vasodilation in rabbit carotid and porcine coronary arteries, reduces acetylcholine‑induced arachidonic acid release, blunts bradykinin‑stimulated Ca²⁺ responses in cultured endothelial cells, and suppresses EDHF release detected by downstream smooth‑muscle membrane potential recordings. The results demonstrate that NO dampens EDHF production and release, and that impaired NO synthesis may preserve endothelial vasodilator function by relieving this intrinsic inhibition.

Abstract

Background The contribution of the endothelium-derived hyperpolarizing factor (EDHF), proposed to be a cytochrome P450–derived metabolite of arachidonic acid, to endothelium-dependent dilatation under physiological conditions has yet to be established, because its effect can be detected only after inhibition of NO synthase and cyclooxygenase. The possibility that NO exerts a feedback inhibition on EDHF formation was studied in isolated perfused arterial segments. Methods and Results Under combined blockade of NO synthase and cyclooxygenase, the EDHF-mediated vasodilatation elicited by receptor-dependent agonists in rabbit carotid and porcine coronary arteries was significantly attenuated by the NO donors C87-3786 and CAS 1609. The endothelium-independent dilatation elicited by isoproterenol was not altered by either NO donor. In N G -nitro- l -arginine–treated carotid artery segments, C87-3786 significantly attenuated the acetylcholine-induced increase in 6-keto-prostaglandin F 1α release, which was taken as an index of arachidonic acid liberation. In parallel experiments using cultured human endothelial cells, C87-3786 attenuated the Ca 2+ response to bradykinin. The release of EDHF from a luminally perfused porcine coronary artery was detected by recording the membrane potential of downstream-situated cultured rat aortic smooth muscle cells. The NO donor C87-3786 had no effect on the hyperpolarization elicited by preformed EDHF but markedly inhibited its release from bradykinin-stimulated donor segments. Conclusions These findings indicate that under physiological conditions, the production of EDHF is damped by NO. Therefore, it follows that when NO synthesis is impaired, alleviation of this intrinsic inhibition may, at least in part, maintain endothelial vasodilator function.