ROBINSON, T. M., D. A. SEWELL, and P. L. GREENHAFF. L-Arginine Ingestion after Rest and Exercise: Effects on Glucose Disposal. Med. Sci. Sports Exerc., Vol. 35, No. 8, pp. 1309–1315, 2003.
Purpose: There is considerable interest, both in health and disease, in enhancing postexercise glucose uptake and glycogen resynthesis in skeletal muscle. The amino acid, arginine, is known to stimulate insulin release and enhance glucose-stimulated insulin release.
Methods: The present investigation examined whether an oral dose of L-arginine (10 g), when given with 70 g carbohydrate (CHO, in the form of simple sugars) improved factors associated with glucose disposal in previously exercised and nonexercised healthy males. The effects of different modes of activity (resistance or cycling exercise) upon these factors were also examined.
Results: Whole-blood glucose and serum insulin concentrations after L-arginine + CHO ingestion were not significantly different from the placebo condition (glycine + CHO ingestion) in all experimental treatments (nonexercised, resistance exercise, and cycling exercise). Similarly, CHO oxidation, forearm blood flow, blood pressure, and heart rate during the postingestion period were unaffected by L-arginine + CHO consumption in all three experimental treatments.
Conclusion: A 10-g oral dose of L-arginine was found to have no effect on blood glucose disposal in human subjects after oral CHO ingestion, either when rested or after different modes of exercise known to differentially affect glucose disposal. These results suggest that the addition of L-arginine to a CHO beverage would not augment postexercise CHO replenishment in healthy human subjects.
When carbohydrate (CHO) is consumed after exercise, the rate of glycogen resynthesis is directly related to the magnitude of the CHO-mediated insulin response (28). Insulin promotes muscle glucose transport (18,24) and increases glycogen synthase activity (17). Therefore, any mechanism capable of enhancing CHO mediated insulin release might augment postexercise glycogen resynthesis.
The amino acid L-arginine, when administered intravenously to humans, has been shown to stimulate insulin release (11). It has also been demonstrated to enhance insulin release induced by glucose (10), possibly by amplifying the glucose-induced signal in the pancreatic β-cell. Another physiological function of L-arginine is as a precursor to nitric oxide, which influences vascular smooth muscle tone. Increased availability of L-arginine has been shown to induce peripheral vasodilation (16) and thereby has the potential to increase muscle blood flow. As a consequence of these latter two effects, L-arginine has been shown to increase insulin-mediated glucose uptake in healthy human subjects (21). Dietary supplementation with relatively large amounts of L-arginine (∼25 g), in humans has been found to result in higher postprandial plasma insulin concentrations (3).
There is considerable interest in the optimization of muscle glucose uptake and glycogen resynthesis during recovery from exercise, as evidenced by the many different CHO-containing beverages marketed for postexercise “energy replenishment.” Prolonged consumption (7 d) of a high-arginine diet (∼ 25 g·d−1), however, was shown to cause excessive loss of sodium in the urine, an associated loss of water and decrease in body weight (3). High doses of L-arginine are also unpalatable (personal observation) and cause gastrointestinal discomfort in some individuals (15). These side effects of high-dose L-arginine consumption could obviously have a negative effect on postexercise CHO repletion.
Exercise mode is known to have a differential effect on postexercise muscle glycogen resynthesis. For example, prolonged concentric exercise depletes muscle glycogen stores and results in rapid glucose transport and the supercompensation of muscle glycogen stores if adequate CHO is supplied in the immediate postexercise period (4). Conversely, resistance exercise is not known to markedly increase muscle insulin sensitivity (8) and exercise that has a significant eccentric component can significantly impair postexercise glycogen resynthesis (9,22).
The purpose of the present study therefore was to determine whether a palatable and tolerated quantity of L-arginine could influence blood flow and the fate of ingested CHO in individuals who had performed no exercise or exercise aimed at altering glucose disposal.
School of Biomedical Sciences, University of Nottingham, Nottingham, UNITED KINGDOM
Address for correspondence: Dr. T. M. Robinson, Centre for Human Nutrition, Coleridge House, Northern General Hospital, Herries Road, Sheffield S5 7AU, United Kingdom; E-mail: firstname.lastname@example.org.
Submitted for publication September 2002.
Accepted for publication March 2003.