[abstract] BENEFICIAL EFFECTS OF HYPEROXIA ON SPLANCHNIC "NO REFLOW" ARE NOT DEPENDENT UPON DIMINISHED ADHERENCE OF LEUKOCYTES TO VASCULAR ENDOTHELIUM

Abstract

BACKGROUND: Ischemia and reperfusion (I/R) induce an acute microvascular inflammatory response that culminates in plugging of blood vessels - the "No Reflow" phenomenon. Hyperoxia has been shown to exert beneficial hemodynamic effects in a number of I/R models. MATERIALS AND METHODS: We studied the effects of oxygen therapy on splanchnic "no reflow" after ischemia and reperfusion (I/R) induced in rats by occlusion of the superior mesenteric artery (SMA) for 40 min. followed by reperfusion (110 min). Four groups were studied: a) Sham-operated controls; b) SMA I/R with air; c) SMA I/R with inhalation of 100percent oxygen started 10 min. before reperfusion; d) SMA I/R with air and infusion of normal saline (NS) 2 ml/kg. Intravital video-microscopy was employed to monitor leukocyte rolling and adhesion to venular endothelium as well as the percentage of totally plugged microvessels, blood flow velocity, and shear rates in the mesenteric microcirculation. RESULTS: SMA I/R caused a decrease in MABP, a 4-7-fold increase in leukocyte rolling (P less than 0.001) and adhesion (P less than 0.001) and a marked increase in the percentage of totally plugged mesenteric microvessels (P less than 0.001). Both inhalation of 100percent oxygen or infusion of NS markedly attenuated leukocyte rolling and adhesion (P less than 0.001) to values not significantly different from sham-operated rats. Hyperoxia and NS totally differed in their effects on microvascular plugging. Hyperoxia caused a dramatic reduction in the percentage of plugged mesenteric microvessels (P less than 0.0001) to values not significantly different from sham-operated rats. In contrast, NS did not exert a significant effect on this parameter. CONCLUSIONS: The marked beneficial effects of oxygen on splanchnic "no reflow" are not solely dependent upon its effects on leukocyte sequestration in the microcirculation.