Enhanced myogenic tone in cerebral arteries from a rabbit model of subarachnoid hemorrhage

Departments of 1 Pharmacology and 2 Surgery, Division of Neurological Surgery, University of Vermont College of Medicine, Burlington, Vermont 05405-0068 Cerebral artery vasospasm is a major cause of death and disability in patients experiencing subarachnoid hemorrhage (SAH). Currently, little is known regarding the impact of SAH on small diameter (100-200 µm) cerebral arteries, which play an important role in the autoregulation of cerebral blood flow. With the use of a rabbit SAH model and in vitro video microscopy, cerebral artery diameter was measured in response to elevations in intravascular pressure. Cerebral arteries from SAH animals constricted more (~twofold) to pressure within the physiological range of 60-100 mmHg compared with control or sham-operated animals. Pressure-induced constriction (myogenic tone) was also enhanced in arteries from control animals organ cultured in the presence of oxyhemoglobin, an effect independent of the vascular endothelium or nitric oxide synthesis. Finally, arteries from both control and SAH animals dilated as intravascular pressure was elevated above 140 mmHg. This study provides evidence for a role of oxyhemoglobin in impaired autoregulation (i.e., enhanced myogenic tone) in small diameter cerebral arteries during SAH. Furthermore, therapeutic strategies that improve clinical outcome in SAH patients (e.g., supraphysiological intravascular pressure) are effective in dilating small diameter cerebral arteries isolated from SAH animals. vascular smooth muscle; vasospasm; intravascular pressure; oxyhemoglobin; Triple H therapy * M. Ishiguro and C. B. Puryear contributed equally to this study.