cyclic-gmp and benzoylarginine-ethyl-ester

To determine whether human alveolar macrophages (AM) generate a compound similar to the endothelium-derived relaxing factor, we studied the effect of AM on the isometric response of the pre-contracted rat aorta preparation in the presence and absence of L-arginine or N-substituted L-arginine compounds. Addition of AM to the pre-contracted aorta preparation was ineffective even in the presence of millimolar concentrations of L-arginine. But, AM in the presence of the substituted L-arginine, N alpha-benzoyl L-arginine ethyl ester, significantly increased vasodilation. The enhanced relaxation was associated with an increase in vascular cyclic guanosine 3,5'-monophosphate formation. Hemoglobin and N omega-nitro L-arginine methyl ester are inhibitors of the endothelium-dependent relaxation, and both attenuated the vasodilation elicited by AM. Human AM were found to metabolize N alpha-benzoyl L-arginine ethyl ester to a citrulline derivative. No such metabolism was observed with L-arginine. A specific, high-pressure liquid chromatographic assay for guanidines revealed that the lack of effect of external L-arginine is not due to the presence of an excess amount of endogenous L-arginine in AM. These results demonstrate that nonactivated human AM, unlike rodent macrophages, possess an enzyme system(s) that metabolize(s) arginine derivatives but not L-arginine to a vasodilator, and this vasodilator has properties similar to that of endothelium-derived relaxing factor. This human AM-derived vasodilator may have an important role in regulating airway smooth muscle function.

Topics: Adult; Animals; Aorta; Arginine; Cyclic GMP; Female; Humans; Macrophage Activation; Macrophages, Alveolar; Male; Rats; Rats, Sprague-Dawley; Vasodilation

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.

Topics: Acetylcholine; Animals; Arginine; Cyclic GMP; Dose-Response Relationship, Drug; Guinea Pigs; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Nitrates; Nitric Acid; Nitric Oxide; Norepinephrine; omega-N-Methylarginine; Pulmonary Artery