SPATIAL AND TEMPORAL CORRELATION BETWEEN LEUKOCYTE BEHAVIOR AND CELL INJURY IN POSTISCHEMIC RAT SKELETAL-MUSCLE MICROCIRCULATION

BACKGROUND: Although leukocyte adhesion and capillary plugging are pos tulated to play a role in postischemic tissue injury, there is only li mited evidence demonstrating the relationship between tissue leukocyte accumulation and cell injury in terms of their temporal sequence and spatial distribution. EXPERIMENTAL DESIGN: This study was designed to study in vivo neutrophil behavior and its correlation with cell injury in postischemic skeletal muscle microcirculation. The microcirculatio n of the rat spinotrapezius muscle was observed in vivo using dual-col or digital microfluorography to simultaneously visualize leukocyte tra ffic and cell death (irreversible nuclear damage) on the basis of carb oxyfluorescein diacetate succinimidyl ester and propidium iodide, resp ectively. A 1-hour period of hemorrhagic hypotension (40 mm Hg) follow ed by reperfusion was carried out to induce muscle injury. RESULTS: Hy potension was followed by an increase in leukocyte recruitment in two different ways: capillary obstruction and venular adhesion. Upon reper fusion, a majority of the leukocytes were initially dispersed from the muscle capillaries and venules, but then the number of leukocytes plu gging capillaries and adherent to venules increased again in a time-de pendent manner. The number of leukocytes obstructing capillaries was c losely correlated with the postischemic systemic blood pressure. The c ell injury became detectable initially at the end of the hypotensive p eriod and then increased explosively after reperfusion before a signif icant leukocyte accumulation. Reperfusion-induced early nuclear injury was seen predominantly in reperfused capillaries without plugging leu kocytes. A majority of the initially damaged nuclei were those of myoc ytes in the pericapillary space, but no nuclei of capillary endotheliu m was involved. Sodium (-)-8-(3-methoxy-4-phenylsulfinylphenyl) pyrazo lo [1,5-a]-1,3,5-triazine-4-olate monohydrate, a novel inhibitor of xa nthine oxidase, significantly attenuated the early increase in muscle injury and subsequent venular leukocyte adhesion after reperfusion. CO NCLUSIONS: These results suggest the involvement of an endothelium-dep endent mechanism involving xanthine oxidase in postischemic irreversib le myocyte injury. It is conceivable that leukocytes adherent to venul es as well as those plugging capillaries play only minor roles in the initial mechanism of reperfusion injury.