title: Endothelial nitric oxide production is tightly coupled to the citrulline-NO cycle.
abstract: Nitric oxide (NO) is an important vasorelaxant produced along with L-citrulline from L-arginine in a reaction catalyzed by endothelial nitric oxide synthase (eNOS). Previous studies suggested that the recycling of L-citrulline to L-arginine is essential for NO production in endothelial cells. However, there is no direct evidence demonstrating the degree to which the recycling of L-citrulline to L-arginine is coupled to NO production. We hypothesized that the amount of NO formed would be significantly higher than the amount of L-citrulline formed due to the efficiency of L-citrulline recycling via the citrulline-NO cycle. To test this hypothesis, endothelial cells were incubated with [14C]-L-arginine and stimulated by various agents to produce NO. The extent of NO and [14C]-L-citrulline formation were simultaneously determined. NO production exceeded apparent L-citrulline formation of the order of 8 to 1, under both basal and stimulated conditions. As further support, alpha-methyl-DL-aspartate, an inhibitor of argininosuccinate synthase (AS), a component of the citrulline-NO cycle, inhibited NO production in a dose-dependent manner. The results of this study provide evidence for the essential and efficient coupling of L-citrulline recycling, via the citrulline-NO cycle, to endothelial NO production.
authors.affiliation: Department of Internal Medicine, College of Medicine, University of South Florida, 12901 Bruce B. Downs Boulevard, Tampa, FL 33612-4799, USA.
authors.forename: Brenda R
authors.initials: BR
authors.lastname: Flam
authors.forename: Duane C
authors.initials: DC
authors.lastname: Eichler
authors.forename: Larry P
authors.initials: LP
authors.lastname: Solomonson
mesh_terms: D000818:Animals; D001011:Aorta / Q000166:cytology; D001120:Arginine / Q000378:metabolism; D001124:Argininosuccinate Synthase / Q000037:antagonists & inhibitors; D001920:Bradykinin / Q000494:pharmacology; D002417:Cattle; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002956:Citrulline / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008954:Models, Biological; D016202:N-Methylaspartate / Q000031:analogs & derivatives / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D014638:Vanadates / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D002956:Citrulline; D009569:Nitric Oxide; D014638:Vanadates; D016202:N-Methylaspartate; C037699:2-methylaspartic acid; D001120:Arginine; D052250:Nitric Oxide Synthase Type III; D001124:Argininosuccinate Synthase; D001920:Bradykinin