Chloroquine induces endothelium-dependent nitric oxide-mediated vasodilation in isolated rat aorta.

Toxic doses of chloroquine induce vasodilation, which contributes to hypotension. In this study, we aimed to investigate the involvement of endothelial nitric oxide in the vasodilatory effect of chloroquine on isolated rat aortas and elucidate the underlying mechanisms. We evaluated the effects of endothelial denudation and several inhibitors, including the nitric oxide synthase inhibitor NW-nitro-L-arginine methyl ester (L-NAME), the non-specific guanylate cyclase (GC) inhibitor methylene blue, the nitric oxide-sensitive GC inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), and the phosphoinositide-3 kinase inhibitor wortmannin, on chloroquine-induced vasodilation in endothelium-intact aortas. The effects of chloroquine and protein phosphatase 2 (PP2) on the phosphorylation of endothelial nitric oxide synthase (eNOS), Src kinase, and caveolin-1 in human umbilical vein endothelial cells were also investigated. Chloroquine-induced vasodilation was more pronounced in endothelium-intact aortas than in endothelium-denuded ones. L-NAME, methylene blue, ODQ, and wortmannin attenuated the vasodilatory effect of chloroquine in endothelium-intact aortas. Chloroquine increased cyclic guanosine monophosphate (cGMP) levels and stimulatory eNOS phosphorylation (Ser1177) while decreasing inhibitory eNOS phosphorylation (Thr495). PP2 inhibited chloroquine-induced phosphorylation of caveolin-1 and Src kinases. These findings suggest that chloroquine-induced vasodilation is mediated by the eNOS-GC-cGMP pathway, with eNOS phosphorylation regulated by caveolin-1 and Src kinase. Methylene blue may alleviate toxic-dose chloroquine-induced vasodilation.