Endothelial dysfunction of coronary resistance arteries is improved by tetrahydrobiopterin in atherosclerosis

Background-Tetrahydrobiopterin (BH4), an essential cofactor for the synthesis of NO, improves endothelial dysfunction after ischemia/reperfusion. Therefore, we hypothesized that reduction of BH4 is involved in the attenuation of endothelium-dependent vasodilation in atherosclerosis, and we investigated the effect of alterations of the BH4 level on the vasodilatory potential of coronary resistance vessels from humans and pigs with atherosclerosis, Methods and Results-Coronary arterioles were obtained from patients undergoing CABG (atherosclerosis group) or valve replacement (control group) and from pigs fed either a standard diet (control group) or atherogenic diet (atherosclerosis group). After isolation, vessels were cannulated, pressurized, and placed on the stage of an inverted microscope. Dose-response curves were Investigated in response to the endothelium-dependent agonists histamine, serotonin, and acetylcholine (for pigs, substance P) and to the endothelium-independent agonist sodium nitroprusside (SNP) under control conditions and before and after incubation of the vessels with sepiapterin (substrate for BH4 synthesis). In vessels fi om patients and from animals with atherosclerosis, compared with vessels from the control groups, there was a significant (P<0.05) reduction of vasodilation to all tested endothelium-dependent agonists but not to SNP. After application of sepiapterin, the responses to the endothelium-dependent agonists but not to SNP were significantly improved in vessels from the atherosclerosis groups. Sepiapterin did not influence vascular reactivity in the control groups. Conclusions-Atherosclerosis severely compromises endothelial function of coronary resistance arteries. Administration of sepiapterin leads to a significant improvement of endothelium-dependent vasodilatation to different agonists in vessels from humans and pigs with atherosclerosis. Therefore, we conclude that a reduced availability of BH4 is involved in the development of endothelial dysfunction in atherosclerosis.