Does l‐citrulline supplementation improve exercise blood flow in older adults?

Abstract

New Findings r What is the central question of this study?Does short-term supplementation with l-citrulline in order to increase l-arginine improve exercise blood flow and peripheral dilatation responses to exercise in older adults? r What is the main finding and its importance? l-Citrulline increased femoral blood flow by 11% and vascular conductance by 14% during lower-limb exercise in older men, whereas no changes were observed in older women. This modest improvement in bulk muscle blood flow in older men has implications for altering muscle metabolism that may result in enhanced exercise tolerance in older adults.l-Citrulline (Cit) increases l-arginine (Arg), the primary substrate for nitric oxide biosynthesis. We tested the hypothesis that muscle blood flow during exercise would be enhanced by Cit supplementation in older adults. Femoral artery blood flow was measured during calf exercise using Doppler ultrasound, and vascular conductance (FVC) was calculated in 25 older adults (13 women and 12 men) before and after 14 days of Cit (6 g day −1 ) and placebo (maltodextrin) in a randomized, double-blind, crossover study. Plasma [Arg] and resting blood pressure were also measured before and after each condition. Women and men were analysed separately because of significant sex-by-condition interactions for the change in exercise blood flow and FVC. Plasma [Arg] was increased by 30 and 35% after Cit (P < 0.01) in women and men, respectively, with no change after placebo. Citrulline lowered diastolic blood pressure in men (75 ± 9 versus 71 ± 6 mmHg, P = 0.02), but this variable remained unchanged in women. Blood flow and FVC during exercise at higher workloads were increased after Cit in men (flow, 521 ± 134 versus 584 ± 166 ml min −1 , P = 0.04; FVC, 5.0 ± 1.5 versus 5.8 ± 1.7 m, min mmHg −1 , P = 0.01) but were not different after placebo. These variables were not altered by Cit in women. Adjusting for baseline diastolic blood pressure removed (P = 0.10) the difference in FBF and FVC following Cit in men. These results indicate that l-citrulline has a modest effect of improving muscle blood flow during submaximal exercise in older men.

Contrast-enhanced ultrasound for determining muscular perfusion after oral intake of L-citrulline, L-arginine, and galloylated epicatechines

“…While some of them were only performed in vitro or in animal models, [ 9 , 14 ] others showed diverging results. [ 16 – 18 , 32 , 39 , 40 ]…”

“…For example, Gonzales et al [ 16 ] measured artery blood flow with doppler ultrasound after L-citrulline supplementation during a standardized exercise and could show that L-citrulline has a modest effect of improving muscle blood flow.…”

“…Previous studies have investigated the impact of these supplements advertised as “NO-boosters” on muscle blood flow or blood volume in resistance trained subjects with diverging results, [ 16 – 19 ] making it challenging to draw a clear conclusion. Compared with the conventional examination tools that have been used in these studies such as strain-gauge plethysmography or Doppler-US, the increasingly applied technique of Contrast-Enhanced Ultrasound (CEUS) allows for a direct visualization of the microperfusion at higher resolution.…”

The Physiological Effects of Amino Acids Arginine and Citrulline: Is There a Basis for Development of a Beverage to Promote Endurance Performance? A Narrative Review of Orally Administered Supplements

“…In addition, many of the health-related applications of L-Cit supplementation are primarily centered on the capacity for L-Cit to increase the availability of L-Arg for NO production [22]. Unlike L-Arg, L-Cit is transported directly to the kidneys after ingestion, where it is then catabolized into L-Arg by arginosuccinate enzymes (synthase and lyase) [37]. Due to the suggested vasodilation activity, supplementation with L-Cit is thought to affect exercise performance positively, gaining increased interest in the sporting and nutrition fields [28].…”

Assessment of muscular perfusion after oral intake of pre-workout nitric-oxide stimulating supplements by Contrast-Enhanced Ultrasound (CEUS). Study protocol for a placebo-controlled, randomized cross-over trial in healthy young males

“…Previous studies have investigated the impact of these supplements advertised as "NO-boosters" on muscle blood flow or blood volume in resistance trained subjects with diverging results (16)(17)(18)(19), making it challenging to draw a clear conclusion. Compared to the conventional examination tools that have been used in these studies such as strain-gauge plethysmography or Doppler-US, the increasingly applied/emerging technique of Contrast-Enhanced Ultrasound (CEUS) allows for a direct visualization of the microperfusion at higher resolution (20,21).…”