TIME-COURSE OF CHANGES IN ARTERIAL RELAXATION FOLLOWING SUBARACHNOID HEMORRHAGE IN DOGS

This experiment determined ii the time course oi inhibition of arteria l relaxation correlates with angiographic vasospasm following subarach noid hemorrhage (SAH) in dogs. Twenty-two dogs underwent cerebral angi ography followed by SAH by 2 injections of blood into the cisterna mag na. Dogs had repeated angiography and were sacrificed 4 (n = 5), 7 (n = 4), 10 (n = 4), 14 (n = 5), or 21 (n = 4) days later. Four dogs serv ed as controls and underwent angiography only, followed by sacrifice. The basilar arteries were removed and studied under isometric tension to determine relaxations to acetylcholine and sodium nitroprusside. Th ere was significant reduction in basilar artery diameter at each time after SAH (day 4: -52% +/- 10%, day 7: -37% +/- 10%, day 10: -54% +/- 10%, day 14: -37% +/- 10%, and day 21: -26% +/- 18%, p < 0.05, analysi s of variance), although there were no pairwise differences in the deg ree of vasospasm over time. Relaxations to acetylcholine were signific antly reduced at all times after SAH (p < 0.05, analysis of variance). Relaxations to sodium nitroprusside were significantly reduced 7 days after SAH. There was a significant linear correlation between increas ing time after SAH and decreasing relaxation to acetylcholine. There w as no correlation in univariate or multivariate analysis, between the time after SAH, the degree of vasospasm and the relaxation to acetylch oline or sodium nitroprusside. It is concluded that inhibition of arte rial relaxation depends on the relaxant used and does not correlate wi th vasospasm. The lack of correlation between angiographic vasospasm a nd relaxation suggests that while the latter occurs after SAH, contrac tile processes may be more important in the pathogenesis oi vasospasm.