Endothelial Hyperpolarization in Humans

The purpose of this study is to elucidate the role Endothelium-Derived Hyperpolarizing Factor (EDHF) plays in dilating blood vessels and whether it differs between healthy people and those with high cholesterol. A second purpose of the study is to determine the identity of EDHF.

The vascular endothelium synthesizes at least four potent vasodilator substances: nitric oxide (NO), prostacyclin, carbon monoxide and endothelium-derived hyperpolarizing factor (EDHF) that contribute to vasodilator tone, and to inhibition of platelet activation and inflammation. EDHF release is stimulated by receptor-dependent agonists such as acetylcholine and bradykinin (BK), and leads to hyperpolarization of the underlying smooth muscle cells presumably by opening Ca2+-activated K+ channels. Indirect pharmacological evidence suggests that EDHF is a cytochrome P450-derived arachidonic acid metabolite, presumably an epoxide. Although the pivotal role of NO to conduit vessel dilation in response to acute increases in shear stress is well known, its' contribution to dilation with sustained increases in flow are minimal, and may be due to EDHF release.

Healthy subjects had venous occlusion plethysmography after intra-arterial infusions of saline, L-NG-monomethyl Arginine (L-NMMA), Tetraethylammonium (TEA), fluconazole, bradykinin, sodium nitroprusside and acetylcholine

Non-hypertensive subjects with cardiovascular risk factors had venous occlusion plethysmography after intra-arterial infusions of saline, L-NG-monomethyl Arginine (L-NMMA), Tetraethylammonium (TEA), fluconazole, bradykinin, sodium nitroprusside and acetylcholine

Intra-arterial infusion of bradykinin at 100, 200, and 400 ng/min. Each dose will be given for 5 minutes.

Intra-arterial infusion of sodium nitroprusside at 1.6 and 3.2 mg/min. Each dose will be given for 5 minutes.

Intra-arterial infusion of acetylcholine at 7.5, 15 and 30 μg/min. Each dose will be given for 5 minutes.

Simultaneous forearm blood flow (FBF) measurements were obtained in both arms using a dual-channel venous occlusion strain gauge plethysmograph at rest and after administration of tetraethylammonium (TEA). Flow measurements were recorded for approximately 7 seconds, every 15 seconds up to eight times and a mean FBF value was computed. Percent change is the difference from baseline FBF and after TEA administration.

Simultaneous forearm blood flow (FBF) measurements were obtained in both arms using a dual-channel venous occlusion strain gauge plethysmograph after administration of L-NG-monomethyl Arginine (L-NMMA). Flow measurements were recorded for approximately 7 seconds, every 15 seconds up to eight times and a mean FBF value was computed. Percent change is the difference in FBF from baseline and after L-NMMA administration.

Percent Change in Forearm Blood Flow (FBF) After Administration of L-NG-monomethyl Arginine (L-NMMA) and Tetraethylammonium (TEA)

Simultaneous forearm blood flow (FBF) measurements were obtained in both arms using a dual-channel venous occlusion strain gauge plethysmograph after administration of L-NG-monomethyl Arginine (L-NMMA) and Tetraethylammonium (TEA). Flow measurements were recorded for approximately 7 seconds, every 15 seconds up to eight times and a mean FBF value was computed. Percent change is the difference in FBF from after L-NMMA administration and after TEA administration.

Simultaneous forearm blood flow (FBF) measurements were obtained in both arms using a dual-channel venous occlusion strain gauge plethysmograph at rest and after administration of fluconazole. Flow measurements were recorded for approximately 7 seconds, every 15 seconds up to eight times and a mean FBF value was computed. Percent change is the difference from baseline FBF and after fluconazole administration.

Percent Change in Forearm Blood Flow (FBF) After L-NG-monomethyl Arginine (L-NMMA) and Fluconazole Administration

Simultaneous forearm blood flow (FBF) measurements were obtained in both arms using a dual-channel venous occlusion strain gauge plethysmograph after L-NMMA administration and administration of fluconazole. Flow measurements were recorded for approximately 7 seconds, every 15 seconds up to eight times and a mean FBF value was computed. Percent change is the difference in FBF after L-NMMA administration and then fluconazole administration.

Percent Change in Forearm Blood Flow (FBF) After Fluconazole and Tetraethylammonium (TEA) Administration

Simultaneous forearm blood flow (FBF) measurements were obtained in both arms using a dual-channel venous occlusion strain gauge plethysmograph after administration of fluconazole and Tetraethylammonium (TEA) administration. Flow measurements were recorded for approximately 7 seconds, every 15 seconds up to eight times and a mean FBF value was computed. Percent change is the difference from FBF after fluconazole administration and after Tetraethylammonium (TEA) administration.

Simultaneous forearm blood flow (FBF) measurements were obtained in both arms using a dual-channel venous occlusion strain gauge plethysmograph after administration of sodium nitroprusside. Flow measurements were recorded for approximately 7 seconds, every 15 seconds up to eight times and a mean FBF value was computed.

Individual net t-PA release at each time point were calculated by the following formula: net release = (Cv-CA) x {FBF x [101-hematocrit/100]}, where Cv and CA represent the concentration of t-PA in the brachial vein and artery, respectively. Change is the difference of t-PA at baseline and t-PA after bradykinin 400 ng/min

Change in Tissue Plasminogen Activator (t-PA) Release After Tetraethylammonium (TEA) and Bradykinin Administration

Individual net t-PA release at each time point were calculated by the following formula: net release = (Cv-CA) x {FBF x [101-hematocrit/100]}, where Cv and CA represent the concentration of t-PA in the brachial vein and artery, respectively. Change is the difference of t-PA after Tetraethylammonium (TEA) and t-PA after bradykinin 400 ng/min

Change in Tissue Plasminogen Activator (t-PA) Release After Fluconazole and Bradykinin Administration

Individual net t-PA release at each time point were calculated by the following formula: net release = (Cv-CA) x {FBF x [101-hematocrit/100]}, where Cv and CA represent the concentration of t-PA in the brachial vein and artery, respectively. Change is the difference of t-PA after fluconazole and t-PA after bradykinin 400 ng/min

Change in Tissue Plasminogen Activator (t-PA) Release After Fluconazole, Tetraethylammonium (TEA), and Bradykinin Administration

Individual net t-PA release at each time point were calculated by the following formula: net release = (Cv-CA) x {FBF x [101-hematocrit/100]}, where Cv and CA represent the concentration of t-PA in the brachial vein and artery, respectively. Change is the difference of t-PA after fluconazole and tetraethylammonium (TEA) and t-PA after bradykinin 400 ng/min

Inclusion Criteria: Hyperlipidemic (LDL > 140) Healthy Volunteer Exclusion Criteria: Pregnancy Diabetes mellitus Cardiovascular Disease Hypertension Use of any regular medications Renal insufficiency Smoking (current or within the past 5 years) Bleeding disorder

Ozkor MA, Murrow JR, Rahman AM, Kavtaradze N, Lin J, Manatunga A, Quyyumi AA. Endothelium-derived hyperpolarizing factor determines resting and stimulated forearm vasodilator tone in health and in disease. Circulation. 2011 May 24;123(20):2244-53. doi: 10.1161/CIRCULATIONAHA.110.990317. Epub 2011 May 9.

Ozkor MA, Hayek SS, Rahman AM, Murrow JR, Kavtaradze N, Lin J, Manatunga A, Quyyumi AA. Contribution of endothelium-derived hyperpolarizing factor to exercise-induced vasodilation in health and hypercholesterolemia. Vasc Med. 2015 Feb;20(1):14-22. doi: 10.1177/1358863X14565374. Epub 2015 Feb 3.

Rahman AM, Murrow JR, Ozkor MA, Kavtaradze N, Lin J, De Staercke C, Hooper WC, Manatunga A, Hayek S, Quyyumi AA. Endothelium-derived hyperpolarizing factor mediates bradykinin-stimulated tissue plasminogen activator release in humans. J Vasc Res. 2014;51(3):200-8. doi: 10.1159/000362666. Epub 2014 Jun 4.

Ozkor MA, Rahman AM, Murrow JR, Kavtaradze N, Lin J, Manatunga A, Hayek S, Quyyumi AA. Differences in vascular nitric oxide and endothelium-derived hyperpolarizing factor bioavailability in blacks and whites. Arterioscler Thromb Vasc Biol. 2014 Jun;34(6):1320-7. doi: 10.1161/ATVBAHA.113.303136. Epub 2014 Mar 27.