CYTOSKELETAL AND EXTRACELLULAR-MATRIX PROTEINS IN CEREBRAL-ARTERIES FOLLOWING SUBARACHNOID HEMORRHAGE IN MONKEYS

It is unclear if vasospasm after subarachnoid hemorrhage (SAH) is predominantly due to smooth-muscle contraction, proliferative vasculopathy, or other changes within the arterial wall such as fibrosis or change in smooth-muscle phenotype. In this study, immunohistochemistry was used to examine changes in extracellular and cytoskeletal proteins in cerebral arteries after SAH that might support one of these mechanisms. Following baseline cerebral angiography, bilateral SAH was created in nine monkeys. Three animals each were killed 7, 14, or 28 days after SAH. Cerebral angiography was repeated on Day 7 in all animals and immediately prior to sacrifice in animals killed on Days 14 and 28. Both middle cerebral arteries and four control basilar arteries were examined using fluorescent antibody techniques with antisera to alpha-actin, myosin, fibronectin, fibrinogen, vimentin, desmin, laminin, and collagens (types I, III, IV, and V). Angiography showed that vasospasm was most severe on Day 7, present but resolving on Day 14, and completely resolved by Day 28. Microscopic study of arterial sections and blinded review of microphotographs of arterial sections by five independent observers did not reveal changes in intensity of density of staining for collagens, desmin, myosin, laminin, or alpha-actin in the tunica media of tunica adventitia. Fibronectin immunoreactivity increased 14 days after SAH. Seven days after SAH, occasional areas of tunica media showed immunoreactivity to fibrinogen. On Day 28, intimal thickening was observed in four of six middle cerebral arteries and this tissue demonstrated immunoreactivity to alpha-actin, myosin, vimentin, desmin, fibronectin, laminin, and each type of collagen. No significant increases in the number of intimal cells showing immunoreactivity to alpha-actin were seen and no significant changes in the hydroxyproline content of cerebral arteries developed at any time after SAH. These results suggest that rigidity and lumen narrowing of vasospasm are not due to increased arterial collagen, although other proteins in the arterial wall or an alteration in cross-linking of existing proteins could produce these changes. There is no indication that smooth-muscle contractile proteins change during vasospasm or that increases in the number of alpha-actin-containing myointimal cells contribute to vasospasm. The occurrence of intimal thickening and increased tunica media fibronectin after vasospasm suggests that vasospasm damages smooth muscle, possibly as a result of intense prolonged smooth-muscle contraction.