The actute effects of a low and high dose of oral L-arginine supplementation in young males at rest


Journal Title (Medline/Pubmed accepted abbreviation): Appl Physiol Nutr Metab
Year: 2011
Volume: 36
Number:
Page numbers:405-411
doi (if applicable):

Summary of background and research design

Hypothesis/background: Arginine is a precursor to the formation of nitric oxide in blood vessels. Because nitric oxide is associated with vasodilation, many athletes utilize arginine supplementation in the attempt to increase blood flow to exercising muscles. Further, some studies suggest that intravenous arginine administration can increase growth hormone response. The authors of this study hypothesized that high dose oral arginine supplementation would increase concentrates of nitric oxide metabolites and hormones (e.g., growth hormone (GH), insulin-like growth factor 1 (IGF-1), and insulin).

Subjects: 14 physically-active male participants (mean age: 25 y, mean weight: 78 kg, mean height: 179 cm, mean protein intake: 1.2 g/kg/day). Subjects were all nonsmokers, nonvegetarian and had not used any other dietary supplements for 12 weeks before the study.

Experimental design: Double-blind, repeated measures with each condition separated by 7 days

Treatments:There were 3 treatment conditions consisting of 500 mL water plus:  1) placebo (flour) in capsule form; 2) 0.075 g/kg body mass L-arginine (~5.9 g for a 78-kg subject); 3)  0.15 g/kg body mass L-arginine (~11.7 g for a 78-kg subject).

Protocol:This study involved the administration of a single dose of each of the above treatments, administered in random order. Subjects refrained from vigorous physical activity the day before testing and came to the laboratory on the morning of testing having fasted 10 h overnight. Blood samples were collected at baseline and at 30, 60, 90, 120, and 180 min following consumption of the test dose. Blood samples were analyzed for arginine, nitrate, nitrite, GH, glucose, IGF-1 and insulin.
 
Summary of research findings
  • Both doses of L-arginine supplementation resulted in comparable and statistically significant increases at all time intervals in plasma L-arginine levels for each arginine dose versus the placebo.  Peak response was typically achieve at 60-90 min post administration and remained elevated at the 180-min interval.
  • Resting plasma nitrate/nitrite was significantly higher (main effect P<0.05) at 0, 30, and 60 min in the high-dose arginine condition compared with the 180-min interval within that condition.  However, there were no significant differences among the 3 treatments at any time interval.
  • There were no significant differences among treatments at any time interval for plasma glucose, GH or IGF-1.
  • There was a significant main effect for insulin, with the 30- and 90-min intervals significantly different (P<0.05) that the 180-min interval.

Interpretation of findings/Key practice applications

Acute L-arginine supplementation, at either a high or low dose, was not associated with increases in NO metabolites, GH, or IGF-1 in young, healthy subjects. This finding is in general agreement with other studies of L-arginine supplementation in similar subject populations.

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