(Stroke. 1999;30:542-545.)
© 1999 American Heart Association, Inc.
Original Contributions |
Brain-Specific Protein C Activation During Carotid Artery Occlusion in Humans
From the Departments of Neurology (R.F.M., D.K.C.) and Surgery (L.A.K.) and the Geriatrics Research Education and Clinical Center (R.F.M.), Baltimore Department of Veterans Affairs Medical Center, University of Maryland School of Medicine, Baltimore,, and the Departments of Molecular and Experimental Medicine and Vascular Biology (J.A.F., A.G., J.H.G.), The Scripps Research Institute, La Jolla, Calif.
Correspondence to Richard Macko, MD, University of Maryland School of Medicine, Department of Neurology, 22 South Greene St, Baltimore, MD 21201-1595. E-mail rmack002{at}umaryland.edu
Background and Purpose—Activation of plasma protein C (PC) zymogen by thrombin-thrombomodulin at the endothelial surface is an important endogenous antithrombotic mechanism. It is unknown whether activated protein C (APC) is generated in vivo in the cerebrovasculature, because there is only limited thrombomodulin expression in human brain vascular endothelium. Therefore, we tested the hypothesis that carotid occlusion produces brain-specific PC activation.
Methods—Blood samples were simultaneously collected from the ipsilateral internal jugular vein and radial artery before and during carotid cross-clamping and on "de-occlusion" in 8 awake patients undergoing routine carotid endarterectomy. Plasma PC zymogen and circulating APC levels were measured using enzyme immunocapture assay and expressed as percent of pooled plasma controls.
Results—Internal jugular vein APC levels increased 28% exclusively during carotid occlusion and then decreased 32% with de-occlusion (F=8.1, P<0.005). PC zymogen increased only 5.9% with occlusion (F=6.3, P<0.02), consistent with hemoconcentration. There were no changes in radial artery PC or APC levels.
Conclusions—These findings demonstrate brain-specific protein C activation in humans during carotid occlusion and suggest a protective role for endogenous APC generation during cerebrovascular occlusion.
Key Words: cerebral ischemia • protein C • stroke • thrombomodulin
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