A systematic review of mechanisms by which natural products of plant origin evoke vasodilatation

This article reviews the body of work aimed at elucidating the mechanisms of action by which natural products of plant origin exert a vasodilatory effect at the level of the vasculature. The search was restricted to 4 mechanisms: the nitric oxide system and (or) reactive oxygen species, the eicosanoid system, potassium channel function, and calcium channel function. The National Library of Medicine database was searched using "PubMed" without restriction to language. The search generated 266 references on 15 November 2005. Most studies were in vitro in nature and of these, most involved studies in the rat aorta. Many of the natural products evoked vasodilatation through an endothelium-dependent mechanism. The vasodilatation was attenuated or abolished by a nitric oxide synthase inhibitor and, in some of these studies, by an inhibitor of guanylate cyclase. A few studies reported a cyclooxygenase component, but most found no effect of the cyclooxygenase inhibitor, indomethacin. The vasorelaxation evoked by several natural products was attenuated by various potassium channel blocking agents, suggesting that some natural products exerted their effect either directly or indirectly through activation of potassium channels. Finally, a significant number of natural products evoked vasodilatation either through blockade of calcium channels or by inhibiting the release of calcium from intracellular stores. Many natural products evoked vasodilatation through multiple mechanisms. The information in this review on mechanisms of action should facilitate good clinical practice by increasing the predictive capabilities of the practitioner, notably the ability to predict adverse effects and interactions among medications. The knowledge should also help to provide leads to the ultimate goal of developing new therapeutic medications.