title: L-arginine does not improve biochemical and hormonal response in trained runners after 4 weeks of supplementation.
abstract: It has been hypothesized that L-arginine improves exercise performance by increasing nitric oxide synthesis and levels of insulin and growth hormone (GH). Metabolic and hormonal responses to chronic L-arginine supplementation may clarify the mechanisms underlying its putative physiologic effects on physical performance. Therefore, the aim of this study was to investigate the effects that 4 weeks of supplementation with L-arginine would have on metabolic and hormonal parameters at rest and in response to exercise. Fifteen healthy runners were divided into treatment (ARG; 6 g L-arginine) and placebo (PLA; 6 g cornstarch) groups. On the first visit, blood samples were collected for baseline, and the supplement or placebo was provided. After 4 weeks of supplementation (second visit), blood samples were collected at the following intervals: at rest, immediately after the first 5-km time-trial running test (5km-TT), immediately after the second 5km-TT, and after 20 minutes of recovery (+20). In addition to exercise performance (total running time), plasma nitrate, nitrite, nitrate plus nitrite, cyclic guanosine monophosphate, lactate, ammonia and serum insulin, GH, insulin-like growth factor 1, and cortisol concentrations were evaluated. There were significant increases in plasma nitrite, cyclic guanosine monophosphate, lactate, ammonia and serum GH, and cortisol at the first 5km-TT, immediately after the second 5km-TT, and +20 in both ARG and PLA. Nitrate plus nitrite and nitrate increased only at +20. No significant change was observed in serum insulin and insulin-like growth factor 1 in any sample period. Total running time did not differ significantly between the 2 tests, in either ARG or PLA. Thus, according to our results, 4 weeks of L-arginine supplementation did not cause beneficial changes in metabolic and hormonal parameters, beyond those achieved with exercise alone.
authors.affiliation: Nucleus of Basic Nutrition and Dietetics, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; Department of Biochemistry, Chemistry Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil. Electronic address: alvares@iq.ufrj.br.
authors.forename: Thiago Silveira
authors.initials: TS
authors.lastname: Alvares
authors.affiliation: Department of Food Technology, Fluminense Federal University, Rio de Janeiro, Brazil.
authors.forename: Carlos Adam
authors.initials: CA
authors.lastname: Conte-Junior
authors.affiliation: Department of Biochemistry, Chemistry Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Joab Trajano
authors.initials: JT
authors.lastname: Silva
authors.affiliation: Department of Biochemistry, Chemistry Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Vânia Margaret Flosi
authors.initials: VM
authors.lastname: Paschoalin
mesh_terms: D000328:Adult; D000641:Ammonia / Q000097:blood; D001120:Arginine / Q000008:administration & dosage*; D006152:Cyclic GMP / Q000097:blood; D019587:Dietary Supplements; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D005260:Female; D006728:Hormones / Q000097:blood*; D019382:Human Growth Hormone / Q000097:blood; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D019344:Lactic Acid / Q000097:blood; D008297:Male; D009566:Nitrates / Q000097:blood; D009569:Nitric Oxide / Q000096:biosynthesis; D009573:Nitrites / Q000097:blood; D010919:Placebos; D012420:Running / Q000502:physiology*
chemical_list: D006728:Hormones; D007328:Insulin; D009566:Nitrates; D009573:Nitrites; D010919:Placebos; D019382:Human Growth Hormone; D009569:Nitric Oxide; D019344:Lactic Acid; D007334:Insulin-Like Growth Factor I; D000641:Ammonia; D001120:Arginine; D006152:Cyclic GMP; D006854:Hydrocortisone
keywords: +20; 5-km time-trial running test; 5km-TT; ADMA; ARG; Amino acids; Exercise; GH; HPLC; Healthy adult runners; Hormones; IGF-1; IP-1; IP-2; NO; NOx; Nitric oxide; Nutritional supplements; PLA; POST; PRE; TRT; after 20-minute recovery; after 4 weeks; after the second 5km-TT; asymmetric dimethylarginine; baseline measurements; cGMP; cyclic guanosine monophosphate; eNOS; endothelial nitric oxide synthase; first 5km-TT; growth hormone; high-performance liquid chromatography; insulin-like growth factor 1; l-arginine–supplemented group; nitrate plus nitrite; nitric oxide; placebo group; total running time