THE INFLUENCE OF VOLUME EXPANSION WITH INDUCED HYPERTENSION ON VESSEL REACTIVITIES, THE BLOOD-BRAIN-BARRIER, AND CEREBRAL INFARCTION IN CATS WITH ONE-HOUR OCCLUSION OF THE MIDDLE CEREBRAL-ARTERY

Thirty anesthetized cats were randomly assigned to three groups of 10 cats each: a 10% hydroxyethyl starch-treated group (10% HAES group), a 6% hydroxyethyl starch-treated group (6% HAES group), or a control group. Cerebral pial arterial reactivities were measured by means of intravital microscopic observation through a cranial window. The middle cerebral artery of the cat was clipped for 1 hour using the transorbital approach, 5 hours later Evans blue dye was injected intravenously, and 30 minutes later the animal was killed. Administration of hydroxyethyl starch or saline was started 15 minutes before clipping and lasted for 1 hour. Total volume administered was 10 ml/kg. Systemic arterial pressure was elevated to about 30 to 40% higher than the resting value by administration of dopamine soon after clipping and maintained for 1 hour. In the hydroxyethyl starch-treated groups, the sizes of infarctions and Evans blue dye leakage were significantly smaller than in the control group. Dye leakage in the 10% HAES group was larger than in the 6% HAES group (statistically significant). Regarding pial arterial reactivites, the caliber of arteries was different in each group after reopening of the clip. Arteries in the control group first returned to some 20% of resting state and redilated 40% or more, arteries in the 6% HAES group returned almost to the resting calibers, and arteries in the 10% HAES group constricted by -20% of the resting calibers. Moreover, 8 of 10 cats in the 10% HAES group showed extravasation of red cells. Only one cat in the 6% HAES group showed extravasation. These findings indicate more prominent impairment of vessel permeability in the ischemic region of the 10% HAES group than of the 6% HAES group. It is concluded that although volume expansion with induced hypertension has beneficial effects on collateral circulation, this regimen may impair the blood-brain barrier remarkably and thus provide negative effects on the brain if a volume expander is used excessively.