TY - JOUR
T1 - Endothelium-derived hyperpolarizing factor determines resting and stimulated forearm vasodilator tone in health and in disease
AU - Ozkor, Muhiddin A.
AU - Murrow, Jonathan R.
AU - Rahman, Ayaz M.
AU - Kavtaradze, Nino
AU - Lin, Ji
AU - Manatunga, Amita
AU - Quyyumi, Arshed A.
PY - 2011/5/24
Y1 - 2011/5/24
N2 - Background-: We assessed the contribution of endothelium-derived hyperpolarizing factors to resting and agonist-stimulated vasodilator tone in health and disease. Tetraethylammonium chloride (TEA) was used to inhibit KCa channel activation and fluconazole was used to inhibit cytochrome P450 2C9-mediated epoxyeicosatrienoic acid synthesis. We hypothesized that endothelium-derived hyperpolarizing factors contribute to resting vascular tone by KCa channel activation and epoxyeicosatrienoic acid release and that endothelium-derived hyperpolarizing factors compensate for reduced nitric oxide bioavailability at rest and with endothelium-dependent vasodilators. Methods and results-: In 103 healthy subjects and 71 nonhypertensive subjects with multiple risk factors, we measured resting forearm blood flow (FBF) using venous occlusion plethysmography before and after intra-arterial infusions of N-monomethyl-L-arginine (L-NMMA), TEA, fluconazole, and their combination. The effects of these antagonists on resting FBF and on bradykinin- and acetylcholine-mediated vasodilation were studied. Resting FBF decreased with TEA and L-NMMA in all subjects (P<0.001); however, the vasoconstrictor response to L-NMMA was greater (P=0.04) and to TEA was lower (P=0.04) in healthy subjects compared with those with risk factors. Fluconazole decreased resting FBF in all subjects, and the addition of TEA further reduced FBF after fluconazole, suggesting that cytochrome P450 metabolites and other hyperpolarizing factor(s) activate KCa channels. Both L-NMMA and TEA attenuated bradykinin-mediated vasodilation in healthy and hypercholesterolemic subjects (P<0.001). In contrast, acetylcholine-mediated vasodilation remained unchanged with TEA in healthy subjects but was significantly attenuated in hypercholesterolemia (P<0.04). Conclusions-: First, by activating TEA-inhibitable KCa channels, endothelium-derived hyperpolarizing factors, together with nitric oxide, contribute to resting microvascular dilator tone. The contribution of KCa channel activation compared with nitric oxide is greater in those with multiple risk factors compared with healthy subjects. Second, activation of KCa channels is only partly through epoxyeicosatrienoic acid release, indicating the presence of other hyperpolarizing mechanisms. Third, bradykinin, but not acetylcholine, stimulates KCa channel-mediated vasodilation in healthy subjects, whereas in hypercholesterolemia, KCa channel-mediated vasodilation compensates for the reduced nitric oxide activity. Thus, enhanced endothelium-derived hyperpolarizing factor activity in conditions of nitric oxide deficiency contributes to maintenance of resting and agonist-stimulated vasodilation.
AB - Background-: We assessed the contribution of endothelium-derived hyperpolarizing factors to resting and agonist-stimulated vasodilator tone in health and disease. Tetraethylammonium chloride (TEA) was used to inhibit KCa channel activation and fluconazole was used to inhibit cytochrome P450 2C9-mediated epoxyeicosatrienoic acid synthesis. We hypothesized that endothelium-derived hyperpolarizing factors contribute to resting vascular tone by KCa channel activation and epoxyeicosatrienoic acid release and that endothelium-derived hyperpolarizing factors compensate for reduced nitric oxide bioavailability at rest and with endothelium-dependent vasodilators. Methods and results-: In 103 healthy subjects and 71 nonhypertensive subjects with multiple risk factors, we measured resting forearm blood flow (FBF) using venous occlusion plethysmography before and after intra-arterial infusions of N-monomethyl-L-arginine (L-NMMA), TEA, fluconazole, and their combination. The effects of these antagonists on resting FBF and on bradykinin- and acetylcholine-mediated vasodilation were studied. Resting FBF decreased with TEA and L-NMMA in all subjects (P<0.001); however, the vasoconstrictor response to L-NMMA was greater (P=0.04) and to TEA was lower (P=0.04) in healthy subjects compared with those with risk factors. Fluconazole decreased resting FBF in all subjects, and the addition of TEA further reduced FBF after fluconazole, suggesting that cytochrome P450 metabolites and other hyperpolarizing factor(s) activate KCa channels. Both L-NMMA and TEA attenuated bradykinin-mediated vasodilation in healthy and hypercholesterolemic subjects (P<0.001). In contrast, acetylcholine-mediated vasodilation remained unchanged with TEA in healthy subjects but was significantly attenuated in hypercholesterolemia (P<0.04). Conclusions-: First, by activating TEA-inhibitable KCa channels, endothelium-derived hyperpolarizing factors, together with nitric oxide, contribute to resting microvascular dilator tone. The contribution of KCa channel activation compared with nitric oxide is greater in those with multiple risk factors compared with healthy subjects. Second, activation of KCa channels is only partly through epoxyeicosatrienoic acid release, indicating the presence of other hyperpolarizing mechanisms. Third, bradykinin, but not acetylcholine, stimulates KCa channel-mediated vasodilation in healthy subjects, whereas in hypercholesterolemia, KCa channel-mediated vasodilation compensates for the reduced nitric oxide activity. Thus, enhanced endothelium-derived hyperpolarizing factor activity in conditions of nitric oxide deficiency contributes to maintenance of resting and agonist-stimulated vasodilation.
KW - endothelium
KW - endothelium-derived vasoconstrictor factors
KW - nitric oxide
KW - vasodilation
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U2 - 10.1161/CIRCULATIONAHA.110.990317
DO - 10.1161/CIRCULATIONAHA.110.990317
M3 - Article
C2 - 21555712
AN - SCOPUS:79958135867
SN - 0009-7322
VL - 123
SP - 2244
EP - 2253
JO - Circulation
JF - Circulation
IS - 20
ER -