The Effect of L-citrulline Supplementation on Cardiovascular and Thermoregulatory Parameters.
(2015) The Effect of L-citrulline Supplementation on Cardiovascular and Thermoregulatory Parameters., no. 44.
Background: Endothelial function is vital to the human body, mediating vasodilation and thermoregulation through the synthesis and release of nitric oxide (NO), a potent vasodilator. In the presence of cardiovascular risk factors, the endothelium undergoes functional and structural changes that impair endothelial function, preceding atherosclerosis and cardiovascular morbidity and mortality. L-citrulline is a semiessential amino acid that is readily converted to L-arginine, a substrate for NO production. This efficient conversion is capable of increasing NO bioavailability, ameliorating endothelial dysfunction with the potential to restore endothelial destruction; improving vascular compliance and cardiovascular risk. Objectives: To investigate the effect of L-citrulline supplementation on cardiovascular and thermoregulatory parameters. Methods: Sixteen young, healthy, normotensive participants were supplemented with either 1.5g of L-citrulline per day (n=8) or placebo (n=8) for a period of two weeks, using a randomised, single blinded, placebo controlled study design. Cardiovascular function was assessed at baseline and after two weeks of supplementation through blood pressure (BP) and the haemodynamic parameters heart rate (HR), pulse wave velocity (PWV) and augmentation index (AIx). Endothelial function was determined by a sympathetic release test (SRT) both at baseline and post-intervention, measuring skin temperature, aural temperature and the time taken for the release of sympathetic tone. Results: The study found that L-citrulline supplementation induced no significant change in factors surrounding cardiovascular function (p>0.05), but trends were evident of a hypotensive effect in the L-citrulline group following supplementation. There was a significant difference in the time take for the release of sympathetic tone (p=0.01) in the intervention group following supplementation, indicative of an improved vasodilatory system. Conclusion: The study concluded that L-citrulline supplementation at a dose of 1.5mg per day induced a profound effect of thermoregulatory parameters, significantly reducing the time taken for the release of sympathetic tone via an increase in NO bioavailability, culminating in an enhanced vasodilatory system. L-citrulline was also observed to cause trends indicative of a hypotensive effect, despite no significant evidence of an improvement in cardiovascular function. Furthermore, this study also validated the SRT as an appropriate and reliable alternative to assessing sympathetic activity; particularly of use to those who are unable to tolerate the cold pressor test, such as those with Raynaud's phenomenon. Key Words: L-citrulline, Thermoregulation, Haemodynamic Parameters, Endothelial Function, Vasodilation, Vascular resistance.