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Department of Physiology, College of Medicine, University of Arizona, Tucson, Arizona 85724-5051
Cross-linked hemoglobin (
-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 quantify the effects of the two Hbs on
microvascular leakage to albumin and to investigate possible changes in
the integrity of the interendothelial cell junctions and the
endothelial actin cytoskeleton. In anesthetized Sprague-Dawley rats,
the microvasculature of a mesenteric window was perfused with
HEPES-buffered saline (HBS) containing 0.5 mg/ml BSA and 2 mg/ml

-Hb (n = 16) or PEG-Hb (n = 5) for 2 or 10 min. Controls
(n = 4) just received HBS-BSA. In some
experiments (n = 9 for 
-Hb ;
n = 5 for PEG-Hb), the perfusate was
then replaced by FITC-albumin in HBS-BSA for the next 3 min. The
vasculature was then perfusion fixed, stained for filamentous actin and
for mast cells, and viewed microscopically. In the remaining
experiments, the mesenteric microvasculature was stained with silver
nitrate to determine the number of endothelial junctional gaps per
length of venules. Both Hbs increased the number and area of leaks per
micrometer of venular length compared with control, but 
-Hb
increased to a greater extent than PEG-Hb. Formation of leaks was
accompanied by changes in the endothelial actin cytoskeleton and by an
increased number of endothelial gaps. Mast cell degranulation was
significantly greater (P < 0.05) in Hb-treated preparations compared with controls, but there was no direct
correlation between sites of degranulation and albumin leakage. These
Hbs appear to induce venular leakage in the mesentery by mechanisms
similar to those previously observed after treatment with histamine or
nitric oxide synthase inhibitors.
blood substitutes; actin cytoskeleton; silver nitrate; microscopy
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