Intravital microscopy of the murine urinary bladder microcirculation.

Objective: To establish an in vivo mouse model of the urinary bladder microcirculation, and characterize the molecular mechanisms of endotoxin-induced leukocyte recruitment. Methods: The murine model was adapted from a technique previously reported for the rat. Mouse bladder microcirculation was observed using intravital microscopy, four hours after intravesical challenge with lipopolysaccharide (LPS) and leukocyteendothelial interactions were examined. Molecular mechanisms of leukocyte recruitment were identified using antibodies to adhesion molecules and chemokines. Results: LPS from Escherichia coli administered intravesically resulted in a significant increase in leukocyte adhesion and rolling at four hours post stimulation. LPS from Pseudomonas aeruginosa administered at similar doses resulted in a significant, but lower increase in leukocyte adhesion after four hours compared with E. coli LPS. Leukocyte adhesion within the bladder microcirculation was dependent on a4-integrins and ICAM-1, whereas leukocyte rolling was P-selectin dependent, but a4-integrin independent. Blockade of MIP-2 and KC did not alter leukocyteendothelial interactions. The bladder endothelium expressed P-selectin, ICAM-1, VCAM-1, MIP-2, and MCP-1. Only VCAM-1 endothelial expression was significantly increased after LPS stimulation. Conclusion: The mouse model of the urinary bladder microcirculation is suitable for the study of inflammatory responses during urinary tract infection (UTI) in vivo.