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First published online September 16, 2005
Journal of Experimental Biology 208, 3665-3674 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01815
Perfusion of the isolated trout heart coronary circulation with red blood cells: effects of oxygen supply and nitrite on coronary flow and myocardial oxygen consumption
1 Institute of Biology, University of Southern Denmark, DK-5230 Odense M,
Denmark
2 Department of Biological Sciences, University of Naples Federico II,
Napoli, Italy
* Author for correspondence (e-mail: fbj{at}biology.sdu.dk)
Accepted 28 July 2005
A method for perfusion of the isolated trout heart coronary circulation
with red blood cells (RBCs) was developed. The method was used to analyse the
influence of RBC perfusion on myocardial O2 supply and
O2 consumption and to test the hypothesis that nitrite is converted
to vasoactive nitric oxide in the RBC-perfused coronary circulation. Perfusion
with RBCs significantly increased myocardial O2 supply and
O2 consumption by increasing the incoming O2
concentration and the O2 extraction. Coronary flow did not differ
between RBC perfusion and saline perfusion, but RBC perfusion established a
strong linear increase in myocardial O2 consumption with coronary
flow. Nitric oxide was measured in the atrial effluent of the preparation.
Perfusion with saline under hypoxic conditions was associated with NO
production. The nitric oxide synthase inhibitor L-NA obliterated this NO
production and significantly decreased coronary flow, showing that the NO was
vasoactive and probably of endothelial origin. RBC perfusion at low
PO2 similarly caused an L-NA-inhibitable NO
production. The change in NO production upon subsequent nitrite addition, by
contrast, was not inhibited by L-NA. Nitrite entered trout erythrocytes
independent of degree of oxygenation, but the O2 saturation of RBCs
showed a major decrease in the coronary circulation, and
[NO2-] decreased while methaemoglobin rose, suggesting
that deoxyHb-mediated reduction of nitrite to NO may have occurred. However,
other possibilities (e.g. NO2-
NO conversion in
myocardial cells) cannot be excluded. The NO formation associated with nitrite
had no effect on coronary flow, possibly because NO was produced after the
resistance vessels.
Key words: erythrocyte, haemoglobin, microcirculation, nitrite, nitric oxide, vasodilation
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