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. NG-monomethyl-L-arginine (L-NMMA; 10-100 microM), a specific inhibitor of NO formation from L-arginine (L-Arg), but not its D-enantiomer (D-NMMA; 100 microM) 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 microM), but not D-NMMA (30 microM), caused a long-lasting inhibition of NO formation which was reversed by L-Arg (30 and 100 microM), but not by D-Arg (100 microM). 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.