To Örebro University

During acute subarachnoid hemorrhage, blood is hemolyzed, which is followed by a significant cerebrovascular spasm resulting in a serious clinical condition. Interestingly, however, the direct vasomotor effect of perivascular hemolyzed blood (HB) has not yet been characterized, preventing the assessment of contribution of vasoconstrictor mechanisms deriving from brain tissue and/or blood and development of possible treatments. We hypothesized that perivascular HB reduces the diameter of the cerebral arteries (i.e., basilar artery [BA]; middle cerebral artery [MCA]) by elevating vascular tissue [Ca2+](i) level. Vasomotor responses were measured by videomicroscopy and intracellular Ca2+ by the Fura2-AM ratiometric method. Adding HB to the vessel chamber reduced the diameter significantly (BA: from 264 +/- 7 to 164 +/- 11 mu m; MCA: from 185 +/- 15 to 155 +/- 14 mu m), which was reversed to control level by wash-out of HB. Potassium chloride (KCl), HB, serum, hemolyzed red blood cell (RBC), plasma, and platelet suspension (PLTs) elicited significant constrictions of isolated basilar arteries. There was a significant increase in K+ concentration in hemolyzed HB (7.02 +/- 0.22 mmol/L) compared to Krebs' solution (6.20 +/- 0.01 mmol/L). Before HB, acetylcholine (ACh), sodium-nitroprussid (SNP), nifedipin, and CO2 elicited substantial dilations in cerebral arteries. In contrast, in the presence of HB dilations to ACh, SNP decreased, but not to nifedipine and CO2. After washout of HB, nitric oxide-mediated dilations remained significantly reduced compared to control. HB significantly increased the ratiometric Ca signal, which returned to control level after washout. In conclusion, perivascular hemolyzed blood elicits significant-nifedipine and high CO2 reversible-constrictions of isolated BAs and MCAs, primarily by increasing intracellular Ca2+, findings that can contribute to the refinement of local treatment of subarachnoid hemorrhage.