title: A possible role of endogenous inhibitor for nitric oxide synthesis in the bovine ciliary muscle.
abstract: The present experiments were designed to investigate the possible role of endogenous methylarginine derivatives such as NG-monomethyl-L-arginine, asymmetrical NG,NG-dimethyl-L-arginine and symmetrical NG,N'G-dimethyl-L-arginine for the nitric oxide synthesis in the bovine ciliary muscle. The contents of asymmetrical NG,NG-dimethyl-L-arginine and symmetrical NG,N'G-dimethyl-L-arginine in the bovine ciliary muscle were determined to be 370.2 +/- 27.6 (n = 5) and 182.4 +/- 22.9 (n = 5) pmoles g-1 wet weight, respectively by means of the automated high-performance liquid chromatography. NG-Monomethyl-L-arginine was below the assay limits. On the basis of the total tissue water content (0.792 +/- 0.006 ml g-1 wet weight, n = 14), the concentrations of asymmetrical NG,NG-dimethyl-L-arginine and symmetrical NG,N'G-dimethyl-L-arginine were tentatively estimated to be (4.7 +/- 0.3) x 10(-7) M (n = 5) and (2.3 +/- 0.3) x 10(-7) M (n = 5), respectively. A23187 (10(-7)-3 x 10(-4) M) produced a concentration-dependent relaxation of the ciliary muscle strips which had been contracted with 10(-5) M carbachol. Authentic asymmetrical NG,NG-dimethyl-L-arginine (3 x 10(-6)-3 x 10(-4) M), but not symmetrical NG,N'G-dimethyl-L-arginine (3 x 10(-4) M), inhibited the 10(-6) M A23187-induced relaxation in a concentration-dependent manner. The inhibition with asymmetrical NG,NG-dimethyl-L-arginine (10(-4) M) was reversed by an addition of 3 x 10(-3) M L-arginine, but not by 3 x 10(-3) M D-arginine. The A23187 (10(-6) M)-induced relaxation was enhanced by 3 x 10(-3) M L-arginine or superoxide dismutase (50 U ml-1), whereas it was inhibited by carboxy-PTIO (3 x 10(-4) M), a scavenger of nitric oxide, or methylene blue (10(-5) M), an inhibitor of guanylate cyclase. The carbachol-induced contraction was enhanced by asymmetrical, NG,NG-dimethyl-L-arginine (10(-5) M) and inhibited by 3 x 10(-3) M L-arginine. Any effect of prostanoid formation during the A23187-induced relaxation was ruled out by using indomethacin (10(-5) M). Sodium nitroprusside (10(-5) M), a donor of nitric oxide, also produced a relaxation, which was inhibited by methylene blue (10(-5) M) or carboxy-PTIO (3 x 10(-4) M) and was augmented by superoxide dismutase (50 U ml-1), but unaffected by asymmetrical NG,NG-dimethyl-L-arginine (3 x 10(-4) M) or L-arginine (3 x 10(-3) M). These results lead us to speculate that the nitric oxide synthesized endogenously from L-arginine may play a role for mediating relaxation of the bovine ciliary muscle and that the endogenous asymmetrical NG,NG-dimethyl-L-arginine may be involved in inhibiting the biosynthesis of nitric oxide when there are increased intracellular concentrations of the methylarginine under certain circumstances.
authors.affiliation: Department of Medicinal Chemistry, Tokyo Medical and Dental University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Azuma
authors.forename: H
authors.initials: H
authors.lastname: Masuda
authors.forename: J
authors.initials: J
authors.lastname: Sato
authors.forename: K
authors.initials: K
authors.lastname: Niwa
authors.forename: T
authors.initials: T
authors.lastname: Tokoro
mesh_terms: D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000032:analysis / Q000502:physiology; D000001:Calcimycin / Q000494:pharmacology; D002417:Cattle; D002924:Ciliary Body / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D007476:Ionophores / Q000494:pharmacology; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D009599:Nitroprusside / Q000494:pharmacology; D019323:omega-N-Methylarginine / Q000032:analysis / Q000502:physiology*
chemical_list: D007476:Ionophores; D009599:Nitroprusside; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D000001:Calcimycin; C018524:N,N-dimethylarginine; D001120:Arginine