Vascular tonus is controlled by endothelium-derived relaxing factor (EDRF), endothelium-derived hyperpolarizing factor (EDHF) and endotheliumderived contracting factor (EDCF) under physiological circumstances. In pathological conditions, impairment of endothelium-derived relaxation can be caused by both decrease in EDRF release and increase in EDCF release. The increase in EDCF is observed with diseases such as hypertension and diabetes. The contribution of Rho-kinase and activated protein kinase (AMPK), which have opposite effects, to the increased EDCF responses was investigated. Rho-kinases are the effectors of Rho which is one of the small guanosine triphosphate-binding proteins. They increase cytosolic Ca+2 concentration and cause vascular smooth muscle to contract, keeping myosin light chain (MLC) in phosphorylated state by affecting myosin phosphatase target subunit which dephosphorylates the MLC. The activities of Rho-kinases increase with the increase of EDCF function. AMPK is the energy sensor of the cell. It provides a vasculoprotective effect by causing endothelium-dependent and endothelium-independent relaxation in smooth muscle. In contrast to Rho-kinase pathway activity, AMPK pathway activity decreases with diseases in which the EDCF function increases. In cases such as diabetes and hypertension that endothelial function impairs toward vasocontraction, it is considered that evaluating Rho-kinase and AMPK pathways which mediate contraction and relaxation in vascular smooth muscle respectively, would provide clues on choosing therapeutic target for pathologies in which endothelial dysfunction is observed.