N alpha-benzoyl-L-arginine ethyl ester (BAEE) is a vasorelaxant which resembles an arginine-containing peptide; its action may be partially endothelium-dependent. Because L-arginine (ARG) has little potency as a vasorelaxant, it has been proposed that an arginine-containing peptide, rather than free ARG, is the immediate precursor of endothelium-derived relaxing factor/nitric oxide (EDRF/NO). In the present study we have characterized pharmacologically the vasorelaxant effect of BAEE and assessed the ability of BAEE to serve as a substrate for EDRF/NO synthesis. BAEE elicited a concentration-dependent vasorelaxation of guinea pig pulmonary artery (EC50 of 0.36 +/- 0.05 mM). This vasorelaxation was neither antagonized by -NG-methyl-L-arginine (100 microM), a competitive inhibitor of EDRF/NO synthesis from ARG, nor potentiated by superoxide dismutase (60 U/ml), a superoxide anion scavenger that prolongs EDRF lifetime. Additionally, compound LY 83583 (1 microM) and methylene blue (10 microM), inhibitors of soluble guanylyl cyclase, failed to block BAEE-induced vasorelaxation. Moreover, endothelium removal potentiated the vasorelaxant effect of BAEE 3-fold. Thus, BAEE-induced vasorelaxation is mediated by a direct action on vascular smooth muscle that is unrelated to EDRF/NO synthesis. Furthermore, ARG, but not BAEE, overcame the inhibition by NG-methyl-L-arginine of the acetylcholine-induced endothelium-dependent cyclic GMP accumulation in guinea pig aortic rings and of A23187-induced nitrite formation by cultured bovine aortic endothelial cells (nitrite is a convenient indicator of NO biosynthesis). Thus, BAEE cannot substitute for ARG as a substrate for EDRF/NO biosynthesis. Collectively, our findings support the notion that free ARG, rather than an arginine-containing peptide related to BAEE, is the immediate biosynthetic precursor of EDRF/NO.