title: Hormonal response to L-arginine supplementation in physically active individuals.
abstract: BACKGROUND
  Nutritional supplements based on the amino acid L-arginine have been hypothesized to improve exercise performance by increasing levels of insulin and growth hormone (GH). Changes of these parameters in response to L-arginine supplementation may clarify the mechanisms underlying its putative physiological effects on physical performance.
  
  
  OBJECTIVE
  The aim of the study was to evaluate the effect of L-arginine supplementation on serum insulin, GH, Growth Factor Insulin-like (IGF-1), and cortisol in response to exercise. Exercise performance was also evaluated.
  
  
  METHODS
  Fifteen trained runners were divided into groups supplemented with 6 g of L-arginine (ARG) or placebo (PLA). Blood samples were collected before supplementation (T0), immediately after the first exercise session (T1), after the second exercise session (T2), and after 20 min of rest (T3). The exercise consisted of two bouts of 5 km time-trial running test.
  
  
  RESULTS
  There was a significant increase in serum GH (T0: 3.28±0.95 vs. 3.21±0.5 ng/mL; T1: 4.35±0.23 vs. 4.17±0.13 ng/mL; T2: 4.22±0.25 vs. 4.17±0.09 ng/mL; T3: 4.14±0.29 vs. 4.13±0.18 ng/mL) and cortisol (T0: 198.71±53.77 vs. 207.57±69.51 nmol/L; T1: 458.16±116.12 vs. 433.26±101.77 nmol/L; T2: 454.61±125.21 vs. 431.88±74.82 nmol/L; T3: 311.14±102.91 vs. 362.26±110.42 nmol/L) after T1, T2, and T3, with no significant difference between the ARG and PLA groups, respectively. There was also no significant difference observed in the variables of IGF-1, insulin, and total running time between the ARG and PLA groups.
  
  
  CONCLUSIONS
  The supplementation of L-arginine did not appear to stimulate the production of insulin, GH, and IGF-1 and, thus, provided no benefit in hormonal response or exercise performance in trained runners.
authors.affiliation: Chemistry Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Davi Vieira Teixeira
authors.initials: DV
authors.lastname: da Silva
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: Chemistry Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Vânia Margaret Flosi
authors.initials: VM
authors.lastname: Paschoalin
authors.affiliation: Chemistry Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil ; Nucleus of Basic Nutrition and Dietetics, Federal University of Rio de Janeiro, Macaé, Brazil.
authors.forename: Thiago da Silveira
authors.initials: Tda S
authors.lastname: Alvares
keywords: amino acids; exercise performance; growth hormone; insulin; nutritional supplements