Endothelial dependent relaxation demonstrated in vivo in cerebral arterioles

The endothelium of mouse pial arterioles was injured in situ with a light/dye technique. The response of the arterioles to acetylcholine or to bradykinin was compared before and after the injury. All vessels failed to dilate after injury. In fact the predominant response now became constriction. The injured vessels were still capable of dilating to papaverine. Uninjured vessels continued to dilate to acetylcholine or bradykinin. The data show that relaxation of pial arterioles to acetylcholine or bradykinin is dependent on a normal endothelium. This is in keeping with demonstrations by others that an endothelial dependent relaxing factor or factors is(are) the mediator of the dilation to either acetylcholine or bradykinin. The present demonstration of such endothelial dependence is important because in contrast with the bulk of the literature it deals with in vivo, rather than in vitro data, and with microcirculation rather than large vessels. It is also important because it concerns brain circulation. The data suggests that endothelial injury, known to occur in a wide variety of pathologic states, could enhance vasospastic potential by eliminating dilating influences and/or converting them to constricting forces.