IN-VIVO FLUORESCENCE MICROSCOPY FOR THE ASSESSMENT OF MICROVASCULAR REPERFUSION INJURY IN SMALL-BOWEL TRANSPLANTS IN RATS

With the use of in vivo fluorescence microscopy we have analyzed micro vascular reperfusion injury of small bowel isograft transplants in rat s. Following 1 hr cold storage in University of Wisconsin solution, th e small bowel was transplanted heterotopically, and the intestinal mic rocirculation was quantitatively analyzed 20-60 min after onset of rep erfusion. The intestinal grafts' capillary perfusion of both the mucos a and the circular and longitudinal muscles was not found altered when compared with the intestinal capillary perfusion of sham-operated con trols. In contrast, leukocyte-endothelial cell interaction, including leukocyte rolling (40+/-5%) and sticking (280+/-100 mm(-2)) in submuco sal postcapillary venules, was significantly increased when compared w ith nontransplanted controls (12+/-8% and 20+/-10 mm(-2), P<0.01 and P <0.05, respectively). Leukocyte-endothelial cell interaction was assoc iated with a marked alteration of lymphatic capillary drainage, as ind icated by the low functional density of lymphatic microvessels of 10.2 +/-6.1 cm (P<0.01 vs. sham-operated controls (39.2+/-6.1 cm(-1)). From these results we propose that leukocyte-endothelial cell interaction, not capillary ''no-reflow,'' is the primary step in the manifestation of microvascular reperfusion injury following a short period of cold ischemia in small bowel grafts.