PHARMACOLOGICAL AND MORPHOLOGICAL EFFECTS OF IN-VITRO TRANSLUMINAL BALLOON ANGIOPLASTY ON NORMAL AND VASOSPASTIC CANINE BASILAR ARTERIES

Despite growing clinical use of transluminal balloon angioplasty (TEA) to treat cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH), the precise mechanism of action of balloon dilation on the cere bral arterial wall is unknown. In this experiment the authors examined the pharmacological and morphological changes in 10 normal and 12 vas ospastic canine basilar arteries following in vitro silicone microball oon TBA. For the SAH group in which the double-hemorrhage model was us ed, vasospasm was confirmed by angiography and the animals were killed on Day 7 after the first SAH. In vitro TEA was performed on basilar a rteries from normal and SAH dogs immediately after sacrifice and remov al of the brain. The procedure was performed while the arteries were m aintained in oxygenated Krebs buffer. In the pharmacological studies, potassium chloride, prostaglandin F-2 alpha, serotonin, and noradrenal ine were used as vasoconstrictors, and bradykinin and calcium ionophor e A23187 were used to produce an endothelium-dependent dilation. In bo th normal and vasospastic groups, the pharmacological responses of dil ated segments of basilar arteries were compared to those of nondilated segments of the same arteries. Vessels from all groups were examined using scanning electron microscopy (EM) and transmission EM. Scanning EM was used to study the intact vessel wall, the smooth-muscle cell la yer obtained after digestion with hydrochloric acid, and the extracell ular matrix obtained after digestion with bleach. Cross-sections of th e vessel wall were examined using trans mission EM. The most striking finding was that immediately after in vitro TBA of both normal and vas ospastic canine basilar arter ies, there was a significant reduction ( p < 0.05) of responses to both vasoconstrictors and vasorelaxants. As revealed by scanning EM and transmission EM, both normal and vasospast ic vessels dilated with TBA showed flattening and patchy denudation of the endothelium, and straightening and occasional rupturing of the in ternal elastic lamina. In addition, vasospastic vessels dilated with T BA showed decreased surface rippling and mild stretching and straighte ning of smooth-muscle cells, and mild thinning of the tunica media. Th ere was no gross vascular disruption or obvious change in the extra ce llular matrix of the vessel walls of either normal or vasospastic arte ries after TBA. These results suggest that functional impairment of va soreactivity in the vessel wall as a result of mechanical stretching o f the smooth-muscle layer plays a more important role than structural alteration, at least in the immediate dilation produced in vasospastic arteries by TBA.