Submucosal collecting venules: a reliable site for intestinal intravital microscopy in rats

Under physiological conditions and after interventions such as ischemia/reperfusion, postcapillary mesenteric venules are most commonly used for in vivo assessment of intestinal microcirculation by intravital microscopy (IVM). In experimental models of gut inflammation, however, IVM was found to be hampered by postinflammatory tissue injury. In this study, postcapillary submucosal collecting venules located at the junction of mesentery and ileum are introduced and evaluated for IVM in a rat model of indomethacin-induced ileitis. The injection of indomethacin was followed by a significant increase in the number of sticking and rolling leukocytes. At the submucosal localization, rollers increased from 5.9 +/- 1.4/0.01 mm(2)/30 s to 34.8 +/- 13.4/0.01 mm(2)/30 s (p <.05), and at the mesentery from 8.0 +/- 2.1/0.01 mm(2)/30 s to 43.1 +/- 13.5/0.01 mm(2)/30 s (p <.05). The number of adherent leukocytes measured at the submucosal level went from 0.21 +/- 0.2/0.01 mm(2)/30 s up to 10.9 +/- 2.9/0.01 mm(2)/30 s (p <.05) and at the mesentery from 0.16 +/- 0.2/0.01 mm(2)/30 s to 15.4 +/- 3.4/0.01 mm(2)/30 s (p <.05). The macroscopic ranking showed an ulcer index of 4.93 +/- 0.76 in the indomethacin group versus 0 in the control group. We found that, despite severe inflammation, this site provided easy and reliable access for IVM. Therefore, we suggest this submucosal site for future studies of intestinal microcirculation in rat models of gut inflammation.