Cocaine-and amphetamine-regulated transcript (CART) peptides are known to be involved in the stress response and have been implicated in the regulation of the cardiovascular system. We evaluated the direct vasoactive properties of CART in the cerebral circulation and its potential mechanisms of action. Penetrating cerebral arterioles, isolated from male Sprague-Dawley rats, were cannulated using a concentric micropipette setup, pressurized and perfused. The vascular response to intraluminal and extraluminal CART peptide was characterized. The endothelium dependence of this response was assessed by means of the endothelial light-dye injury model. The nonspecific endothelin receptor antagonist PD-145065, the ET A -specific antagonist BQ-123, the ET Bspecific antagonist BQ-788, and the inhibitor of endothelin-converting enzyme phosphoramidon were used to characterize the involvement of the endothelin pathway in the vascular response to CART peptide. Extraluminal and intraluminal application of CART peptide (0.1 nm to 1 lmol/L) evoked a long-lasting dose-dependent constriction of isolated penetrating cerebral arterioles to B80% of resting myogenic tone. Disruption of the endothelium by the endothelial light/dye injury model resulted in the abolition of this response (Po0.05). Extraluminal administration of PD-145065, BQ-123, and phosphoramidon blocked the constriction response to CART peptide (Po0.01). The ET B antagonist, BQ-788, did not alter the constriction response to CART peptide. Cocaine-and amphetamine-regulated transcript peptide is a potent vasoconstrictor in the cerebral circulation. Its direct vasoactive properties are endothelium-dependent and are mediated by ET A , not ET B , endothelin receptors.