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From the School of Animal and Microbial Sciences, University of Reading, Reading, United Kingdom.
Correspondence to Dr P.D. Weinberg, School of Animal and Microbial Sciences, University of Reading, Whiteknights PO Box 228, Reading RG6 6AJ, United Kingdom. E-mail p.d.weinberg{at}reading.ac.uk.
Abstract Uptake of circulating albumin by the aortic
wall is greater downstream than upstream of branches in immature
rabbits, but the opposite pattern occurs in mature animals. We
investigated the role of NO in determining these variations. Descending
thoracic aortas of rabbits were cannulated using techniques that avoid
depressurization, overstretching, and excessive fluid dynamic stresses
at the endothelial surface. They were perfused in situ
at a constant pressure and flow rate with oxygenated,
protein-containing physiological buffer, with or
without
N
-monomethyl-L-arginine,
an inhibitor of NO synthesis. Aortas were fixed 7 to 8
minutes after the addition of rhodamine-labeled albumin to this
perfusate, and uptake of the tracer near intercostal ostia was
measured by digital imaging fluorescence microscopy of sections
through the wall. Despite the absence of pulsatile flow, blood cells,
and many plasma components, patterns of transport in control
experiments were the same as those occurring in vivo; uptake was
greatest downstream of ostia in immature vessels and upstream in mature
ones, although mean uptake was higher than previously reported. In the
presence of the inhibitor, mean uptake in immature arteries
was elevated threefold and the maximum tracer concentration occurred
deeper in the wall, but there was no change in the fractional
difference between regions. Conversely, the reverse of the control
pattern of transport was observed in mature arteries exposed to the
inhibitor, but there was no change in mean uptake. The
reversal was almost entirely prevented by adding excess
L-arginine to the perfusate and was
largely stereospecific. Endogenous NO thus appears to
determine the mature pattern of transport near branches and helps to
maintain the barrier function of the immature wall.
Key Words: age arterial branches arterial permeability endothelium-derived relaxing factor nitric oxide
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