QUANTITATIVE-ANALYSIS OF SMALL-INTESTINAL MICROCIRCULATION IN THE MOUSE

Impairment of intestinal nutritive perfusion and accumulation of infla mmatory cells in the intestinal microvasculature are well-known sequel ae of mesenteric ischemia/reperfusion, sepsis, and shock. However, the molecular mechanisms underlying these alterations are still not fully understood. The mouse is particularly suitable for the study of these mechanisms since in this species the involvement of, for example, adh esion receptors or pro-/anti-adhesive mediators can be selectively inv estigated by the use of monoclonal antibodies or gene-targeted strains . The aim of our present study was, therefore, to establish a model to investigate the microcirculation in the mouse small intestine. Under anesthesia by inhalation of isoflurane-N2O, Balb/c mice (n=16) were la parotomized, and a segment of the jejunum was exteriorized for intravi tal fluorescence microscopy. Using FITC-dextran (MW 150,000) as a plas ma marker, functional capillary density (FCD) of both the intestinal m ucosa and muscle layer was analyzed. Nutritive perfusion was homogeneo us in both compartments with values for FCD of 512+/-15 cm(-1) in muco sa and 226+/-21 cm(-1) in the muscle layer. No significant changes wer e observed throughout the observation period of 2 h (FCD values at the end of the observation period: 524+/-31 cm(-1) and 207+/-7 cm(-1) in mucosa and muscle, respectively). Besides capillary perfusion, leukocy te-endothelial cell interaction was analyzed in postcapillary venules of the intestinal submucosa using rhodamine-6G as an in vivo leukocyte stain. Under physiological conditions only a few white blood cells we re found rolling along or firmly adherent to the microvascular endothe lium (number of rolling leukocytes 1+/-0.2 cells/mm per second; number of adherent leukocytes: 18+/-7 cells/mm(2)). In a separate group rhod amine-6G-labeled syngeneic platelets were infused to analyze platelet- endothelial cell interactions quantitatively in vivo. Platelets rolled along or attached to the endothelium in a manner similar to leukocyte s. However, in contrast to leukocytes the interactions were not restri cted to venules, but were also observed in small arterioles. The newly established model allows for the visualization and quantitative asses sment of both nutritive perfusion and platelet/leukocyte-endothelial c ell interactions within the distinct layers of the mouse small intesti ne. Using this model in combination with gene-targeted mice or monoclo nal antibodies it is possible to investigate the molecular mechanisms of intestinal inflammation reactions.