Endothelium-dependent dilation to L-arginine in isolated rat skeletal muscle arterioles

The vascular actions of L-arginine (L-Arg) were studied in isolated, pressurized first-order rat cremaster muscle arterioles (93 +/- 2.9 microns) bathed in a Krebs bicarbonate-buffered solution, pH 7.4, equilibrated with 21% O2-5% CO2. Arterioles were studied before and after either the administration of NG-nitro-L-arginine (L-NNA, 10(-3) M), an inhibitor of the synthesis of endothelium-derived relaxing factor (EDRF), or the removal of the endothelium. Acetylcholine (ACh, 10(-8) and 10(-6) M), sodium nitroprusside (SNP, 10(-8) M) and phenylephrine (PE, 10(-7) M) evoked dilation and constriction, respectively. L-Arg, (10(-5)-10(-3) M) the precursor of EDRF, evoked dose-dependent arteriolar dilation; whereas D-arginine (D-Arg, 10(-5)-10(-3) M) was without any significant effect. Administration of L-NNA significantly reduced basal diameters and significantly inhibited the arteriolar dilations to both ACh and L-Arg but had no effect on the dilation to SNP. Removal of the arteriolar endothelium with air inhibited dilations to both ACh and L-Arg, had no effect on responses to SNP, and potentiated vasoconstrictor responses to PE. These findings suggest that in skeletal muscle arterioles the dilations to ACh and L-Arg are endothelium dependent and that microvascular endothelium modulates constrictor responses to PE. Thus EDRF may play an important role in the local regulation of arteriolar resistance and blood flow.