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

Abstract

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 O(2) supply and O(2) 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 O(2) supply and O(2) consumption by increasing the incoming O(2) concentration and the O(2) extraction. Coronary flow did not differ between RBC perfusion and saline perfusion, but RBC perfusion established a strong linear increase in myocardial O(2) 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 P(O(2)) 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 O(2) saturation of RBCs showed a major decrease in the coronary circulation, and [NO(2)(-)] decreased while methaemoglobin rose, suggesting that deoxyHb-mediated reduction of nitrite to NO may have occurred. However, other possibilities (e.g. NO(2)(-)-->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.