Impaired endothelial function may be due to decreased aortic tetrahydrobiopterin, assessed by a new flow-mediated vasodilation in vivo in hypercholesterolemic/atherogenic mice.

Tetrahydrobiopterin (BH4) is an important cofactor for endothelial nitric oxide synthase activity. The relationship between endothelial function in vivo and aortic BH4 level is not fully understood, however. In the present study, we aimed to clarify whether reduction of aortic BH4 levels contributes to endothelial dysfunction in vivo using spontaneously hyperlipidemic mice. To estimate endothelial function in vivo and in real-time state, we developed a flow-mediated vasodilation (FMV) method in mice, which measured changes in the diameter of the femoral artery in response to increased blood flow. C57BL/6 mice and apoE/low-density lipoprotein receptor double knock-out mice were fed a low-fat diet (LFD) or a high-fat diet (HFD) for 12 weeks from 6 weeks of age. HFD feeding impaired FMV in double knock-out mice, but not in C57BL/6 mice. Furthermore, HFD feeding reduced plasma NOx concentration and aortic BH4 level in double knock-out mice. Conversely, exogenous injection of BH4 (2 mg/kg) markedly increased aortic BH4 levels and restored endothelial function. In conclusion, we demonstrated that HFD feeding impaired nitric oxide-mediated endothelial function and reduced BH4 level in vivo, and that acute augmentation of aortic BH4 levels improved endothelial function. These findings indicate that BH4 is a critical determinant of nitric oxide-mediated endothelial function in hypercholesterolemia.