ENDOCANNABINOIDS - A NEW CLASS OF VASOACTIVE SUBSTANCES

Endogenous cannabinoids (endocannabinoids) have recently been identifi ed in the CNS and attention has now turned to their cardiovascular act ions. The prototypic endocannabinoid, anandamide, derived from arachid onic acid, has been shown to be a vasorelaxant, particularly in the re sistance vasculature. This vasorelaxation has been shown to be both en dothelium-independent and -dependent, depending on the vascular bed. I t has been proposed that an endocannabinoid may mediate the nitric oxi de- and prostanoid-independent component of endothelium-dependent rela xations, as these responses are sensitive to a cannabinoid receptor an tagonist and show similarities to anandamide-induced relaxations. This hypothesis has generated much controversy and the emerging conflicts in the literature are discussed in this article by Michael Randall and David Kendall. Despite this controversy, it has recently been shown t hat anandamide is produced by endothelial cells. Clearly, much work is required to adequately define the physiological significance of endoc annabinoids in the cardiovascular system.