Intravital Microscopy of the Murine Urinary Bladder Microcirculation

Catheter associated urinary tract infection (UTI) is one of the most common nosocomial infections. The objective of this study was to establish an in vivo mouse model of the urinary bladder microcirculation to study the inflammatory response to UTI. Female C57Bl/6 mice were challenged intravesically with 0.1, 0.5, 1, 5 or 7 mg/kg of Escherichia coli lipopolysaccharide (LPS) or saline. 3.5 hrs later, the right jugular vein was cannulated, a catheter was inserted into the bladder, the urine drained and 100 μl of warm saline injected. The bladder was gently exteriorized and the bladder microcirculation was recorded for the next hour. In some mice, leukocyte endothelial cell interactions were observed after exposure to anti‐P‐selectin or anti‐α 4 ‐integrin Ab. LPS at a dose of 5 and 7 mg/kg resulted in a significant increase in leukocyte adhesion and rolling. Leukocyte adhesion at 4 and 4.5 hrs post saline stimulation was 0.9±1.0 and 2.7±1.0 cells/field of view, respectively, and the flux of rolling leukocytes was 21±6.4 and 47±22 cells/min. Leukocyte adhesion at the two time points after 5 mg/kg of LPS stimulation was 17±7.8 and 21±8.0 cells/field of view, respectively, and the flux of rolling leukocytes was 74±17 and 116±56 cells/min. Blockage of α 4 ‐integrin had no effect on leukocyte rolling, whereas the use of a P‐selectin Ab significantly inhibited leukocyte rolling (54.0± 26.0 to 1.25±0.97 cells/min, p<0.05). These results demonstrate that baseline conditions are maintained within the first half‐hour of microcirculatory observations. Leukocyte rolling within the bladder microcirculation is P‐selectin dependent but α 4 ‐integrin independent. This model can be used to decipher the molecular mechanisms of leukocyte recruitment into the bladder as well as to examine in vivo responses to catheter materials and bacterial infection.