Evidence of transcellular albumin transport after hemorrhagic shock.

Hemorrhagic shock-induced ischemia-reperfusion injury is characterized by an increase in microvascular permeability. This increase in permeability is thought to occur mainly via passive transport through interendothelial cell junctions. However, recent data have suggested that a transcellular (caveolae) transport mechanism(s) may also play a role after shock. The purpose of our study was to investigate the role of caveolae transport after hemorrhagic shock. After a control period, blood was withdrawn to reduce the mean arterial pressure to 40 mmHg for 1 h in urethane-anesthetized Sprague-Dawley rats. Mesenteric postcapillary venules in a transilluminated segment of small intestine were examined to determine changes in permeability. Rats received an intravenous injection of fluorescein isothiocyanate-bovine albumin during the control period. The fluorescent light intensity emitted from the fluorescein isothiocyanate-bovine albumin was recorded with digital microscopy within the lumen of the microvasculature and was compared with the intensity of light in the extravascular space. The images were downloaded to a computerized image analysis program that quantitates changes in light intensity. This change in light intensity represents albumin extravasation. Our results demonstrated a marked increase in albumin leak after hemorrhagic shock that was significantly attenuated with two different inhibitors of transcellular transport, N-ethylmaleimide and methyl-beta-cyclodextrin. These data suggest that caveolae transport plays a significant role in microvascular permeability after hemorrhagic shock.