Quantitative analysis of small intestinal microcirculation in the mouse

Impairment of intestinal nutritive perfusion and accumulation of inflammatory cells in the intestinal microvasculature are well-known sequelae 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, adhesion receptors or pro-/anti-adhesive mediators can be selectively investigated 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 laparotomized, and a segment of the jejunum was exteriorized for intravital fluorescence microscopy. Using FITC-dextran (MW 150,000) as a plasma marker, functional capillary density (FCD) of both the intestinal mucosa and muscle layer was analyzed. Nutritive perfusion was homogeneous in both compartments with values for FCD of 512+/-15 cm(-1) in mucosa and 226+/-21 cm(-1) in the muscle layer. No significant changes were 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, leukocyte-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 were found rolling along or firmly adherent to the microvascular endothelium (number of rolling leukocytes 1+/-0.2 cells/mm per second; number of adherent leukocytes: 18+/-7 cells/mm(2)). In a separate group rhodamine-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 leukocytes. However, in contrast to leukocytes the interactions were not restricted to venules, but were also observed in small arterioles. The newly established model allows for the visualization and quantitative assessment of both nutritive perfusion and platelet/leukocyte-endothelial cell interactions within the distinct layers of the mouse small intestine. Using this model in combination with gene-targeted mice or monoclonal antibodies it is possible to investigate the molecular mechanisms of intestinal inflammation reactions.