Plasma citrulline concentration, a marker for intestinal functionality, reflects exercise intensity in healthy young men

• Published in: Clinical nutrition (Edinburgh, Scotland) Scotland), 2019-10, Vol.38 (5), p.2251-2258
• Main Authors: Kartaram, Shirley, Mensink, Marco, Teunis, Marc, Schoen, Eric, Witte, Gerrit, Janssen Duijghuijsen, Lonneke, Verschuren, Martie, Mohrmann, Karin, M'Rabet, Laura, Knipping, Karen, Wittink, Harriet, van Helvoort, Ardy, Garssen, Johan, Witkamp, Renger, Pieters, Raymond, van Norren, Klaske
• Format: Article
• Language: English
• Subjects: Citrulline; Exercise intensity; Glutamine; Intestinal fatty acid binding protein; Intestinal function
• ISSN: 0261-5614; 1532-1983
• DOI: 10.1016/j.clnu.2018.09.029

Plasma citrulline concentration is considered to be a marker for enterocyte metabolic mass and to reflect its reduction as may occur during intestinal dysfunction. Strenuous exercise can act as a stressor to induce small intestinal injury. Our previous studies suggest that this comprises the intestinal ability to produce citrulline from a glutamine-rich protein bolus. In this study we investigated the effects of different exercise intensities and hydration state on citrulline and iFABP levels following a post-exercise glutamine bolus in healthy young men. Fifteen healthy young men (20–35 yrs, VO2 max 56.9 ± 3.9 ml kg−1 min−1) performed in a randomly assigned cross-over design, a rest (protocol 1) and four cycle ergometer protocols. The volunteers cycled submaximal at different percentages of their individual pre-assessed maximum workload (Wmax): 70% Wmax in hydrated (protocol 2) and dehydrated state (protocol 3), 50% Wmax (protocol 4) and intermittent 85/55% Wmax in blocks of 2 min (protocol 5). Immediately after 1 h exercise or rest, subjects were given a glutamine bolus with added alanine as an iso-caloric internal standard (7.5 g of each amino acid). Blood samples were collected before, during and after rest or exercise, up to 24 h post onset of the experiment. Amino acids and urea were analysed as metabolic markers, creatine phosphokinase and iFABP as markers of muscle and intestinal damage, respectively. Data were analysed using a multilevel mixed linear statistical model. p values were corrected for multiple testing. Citrulline levels already increased before glutamine supplementation during normal hydrated exercise, while this was not observed in the dehydrated and rest protocols. The low intensity exercise protocol (50% Wmax) showed the highest increase in citrulline levels both during exercise (43.83 μmol/L ± 2.63 (p