Cross-linked hemoglobin (αα-Hb) and polyethylene glycol (PEG)-conjugated Hb have both been considered as possible "blood substitutes." Previously, we showed that PEG-Hb extravasates rapidly in the intestinal mucosa and causes transient epithelial sloughing, resulting in temporary opening of the intestinal epithelial barrier. In the present study, the rat mesenteric preparation was used to quant...