Endothelium-dependent relaxation and vasospasm in the single-hemorrhage canine model

We have investigated the relationship between angiographic vasospasm and the ability of spastic vessels to relax in response to agents which promote release of endothelium derived relaxing factor. Vasospasm was induced in dogs by the 'single hemorrhage' technique. Animals received a single intracisternal injection of blood, blood activated with thromboplastin or collagen, or inert material, and angiograms were obtained day 0 and day 7. Vasospasm was estimated by measuring the ratio of the diameter of the vessel before and after treatment. Rings of cerebral artery obtained from these animals were suspended in a standard organ-bath arrangement, contracted with prostaglandin F2 alpha and then treated with increasing doses of adenosine triphosphate or bradykinin, both of which cause relaxation by an endothelium-dependent process. The arteries from animals with moderate to severe vasospasm showed a response to bradykinin and adenosine-triphosphate which was reduced, absent or converted to a contraction, when compared with normal vessels. Vessels in which vasospasm was mild or absent relaxed as expected to these agents. The reduction in vessel diameter showed a highly significant correlation with the reduction in relaxation to bradykinin or adenosine-triphosphate. These results have demonstrated that impairment of endothelium-dependent vasorelaxation correlates with the existence of vasospasm.