Background and Purpose-Leukocytes contribute to cerebral ischemia-reperfusion injury. However, few experimental models examine both in vivo behavior of leukocytes and microvascular rheology after stroke. The purpose of the present study was to characterize patterns of leukocyte accumulation in the cerebral microcirculation and to examine the relationship between leukocyte accumulation and microcirculatory hemodynamics after middle cerebral artery occlusion and reperfusion (MCAO-R). Methods-Male rats (250 to 350 g) were anesthetized and ventilated. Tail catheters were inserted for measurement of arterial blood gases and administration of drugs. Body temperature was maintained at 37°C. Animals were subjected to 2 hours of MCAO by the filament method. A cranial-window preparation was performed, and the brain was superfused with warm, aerated artificial cerebrospinal fluid. Reperfusion was initiated by withdrawing the filament, and the pial microcirculation was observed by use of intravital fluorescence microscopy. Leukocyte accumulation in venules, arterioles, and capillaries; leukocyte rolling in venules; and leukocyte venular shear rate were assessed during 1 hour of reperfusion. Results-We found significant leukocyte adhesion in cerebral venules during 1 hour of reperfusion after 2 hours of MCAO.Leukocyte trapping in capillaries and adhesion to arterioles after MCAO-R tended to increase compared with controls, but the increase was not significant. We also found that shear rate was significantly reduced in venules during early reperfusion after MCAO. Conclusions-A model using the filament method of stroke and fluorescence microscopy was used to examine white-cell behavior and hemodynamics in the cerebral microcirculation after MCAO-R. We observed a significant increase in leukocyte rolling and adhesion in venules and a significant decrease in blood shear rate in the microcirculation of the brain during early reperfusion. Leukocytes may activate and damage the blood vessels and surrounding brain cells, which contributes to an exaggerated inflammatory component to reperfusion. The model described can be used to examine precisely blood cell-endothelium interactions and hemodynamic changes in the microcirculation during postischemic reperfusion. Information from these and similar experiments may contribute to our understanding of the early inflammatory response in the brain during reperfusion after stroke.

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Hepatic ischemia followed by reflow results in a myriad of metabolic and circulatory derangements that may eventually result in liver failure and death. In the present experiments we have used the technique of intravital fluorescence microscopy with fluoroscein isothiocyanate conjugated to bovine serum albumin as the intravascular fluorochrome to study the effects of ischemia and reperfusion on the hepatic microcirculation in vivo. Total hepatic ischemia was produced for 90 min to the left and median lobes of pentobarbital-anesthetized rats. After ischemia, reflow was allowed for 2 h. Three groups were studied: sham-ischemia controls and rats treated with either 1 ml saline or 12.5 mumol ATP-MgCl2 in 1-ml volume at the beginning of reflow. Although control rats exhibited stable microcirculation throughout the experiment, in saline-treated rats the number of perfused centrilobular areas and perfused sinusoids per unit area on the surface of the liver was decreased to approximately 50 and 40% of sham-ischemia controls, respectively. However, in rats treated with ATP-MgCl2 the density of perfused centrilobular areas and perfused sinusoids was 86 and 80% of sham-ischemia controls, respectively. From these results we conclude that intravital fluorescence microscopy is a potentially valuable method for the study of the hepatic microcirculation in vivo. Moreover, the results with ATP-MgCl2 treatment indicate that its effect on the microcirculation is a major factor in its beneficial effects on hepatic function after ischemia and reflow.

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Alterations in fiber size and capillary diameter were highly correlated with perfusion deficits after myocardial ischemia. After 5 (n = 3) and 30 (n = 5) min of global normothermic ischemia, isolated rabbit hearts were perfused with India ink and then with glutaraldehyde. Morphometric techniques were used to determine mean fiber cross-sectional area [a(f)], mean effective capillary diameter [d(c)], total and perfused capillary number per fiber area, and capillary length per fiber volume in subepicardium (Epi) and subendocardium (Endo). Sarcomere length was measured to differentiate between effects of fiber shortening and intracellular edema on a(f). After 30 min of ischemia, a(f) increased 41 (Epi) and 36% (Endo). Of these percentages, fiber shortening accounted for 2 (Epi) and 25% (Endo). Decreased d(c) was correlated with increased a(f) as well as reductions in perfused capillary number and length. Whereas intracellular edema had the greatest overall effect on a(f), fiber shortening accounted for a significant increase of a(f) in Endo, where perfusion deficits were most pronounced. These data support the hypothesis that microvascular compression consequent to increased a(f) contributes to perfusion deficits after myocardial ischemia.