Nitric oxide synthesized from L-arginine regulates vascular tone in the coronary circulation of the rabbit

Abstract

1 The role of nitric oxide (NO) in the regulation of the vascular tone of the coronary circulation of the Langendorff-perfused rabbit heart was investigated. 2 N^G-monomethyl-L-arginine (L-NMMA; 10–100 μm), a specific inhibitor of NO formation from L-arginine (L-Arg), but not its D-enantiomer (D-NMMA; 100 μm) produced a dose-related, sustained increase in the coronary perfusion pressure (CPP). In addition, L-NMMA inhibited the vasodilator responses of acetylcholine (ACh), unmasking in some instances its direct vasoconstrictor effect. These effects of L-NMMA were attenuated by L-Arg. 3 L-NMMA (10 and 30 μm), but not D-NMMA (30 μm), caused a long-lasting inhibition of NO formation which was reversed by L-Arg (30 and 100 μm), but not by D-Arg (100 μm). 4 This study indicates that the formation of NO from L-Arg in the coronary circulation of the rabbit plays a role both as a regulator of vascular tone and as a mediator of the vasodilatation induced by ACh.