Effect of citrulline on muscle functions during moderate dietary restriction in healthy adult rats

Low calorie diets are designed to reduce body weight and fat mass, but they also lead to a detrimental loss of lean body mass, which is an important problem for overweight people trying to lose weight. In this context, a specific dietary intervention that preserves muscle mass in people following a slimming regime would be of great benefit. Leucine (LEU) and Citrulline (CIT) are known to stimulate muscle protein synthesis (MPS) in post-prandial and post-absorptive state, respectively. This makes them interesting bioactive components to test in the context of dietary restriction. We tested the concept of combining LEU and CIT in adult female rats. We postulated that the sequential administration of LEU (mixed in chow) and CIT (given in drinking water before a rest period) could be beneficial for preservation of muscle function during food restriction. Sixty female rats (22 weeks old) were randomized into six groups: one group fed ad libitum with a standard diet (C) and five food-restricted groups (60 % of spontaneous intake for 2 weeks) receiving a standard diet (R group), a CIT-supplemented diet (0.2 or 1 g/kg/day, CIT0.2 group and CIT1 group, respectively), a LEU-supplemented diet (1.0 g/kg/day) or a CIT + LEU-supplemented diet (CIT + LEU 1.0 g/kg/day each). At the end of the experiment, body composition, muscle contractile properties and muscle protein synthesis (MPS) rate were studied in the tibialis anterior muscle. Dietary restriction tended to decrease MPS (R: 2.5 +/- A 0.2 vs. C: 3.4 +/- A 0.4 %/day, p = 0.06) and decrease muscle strength (R: 3,045 +/- A 663 vs. C: 5,650 +/- A 661 A.U., p = 0.03). Only CIT administration (1 g/kg) was able to restore MPS (CIT1: 3.4 +/- A 0.3 vs. R: 2.5 +/- A 0.2 %/day, p = 0.05) and increase muscle maximum tetanic force (CIT1: 441 +/- A 15 vs. R: 392 +/- A 22 g, p = 0.05) and muscle strength (CIT1: 4,259 +/- A 478 vs. R: 3,045 +/- A 663 A.U., p = 0.05). LEU had no effect and CIT + LEU supplementation had few effects, limited to adipose mass and fatigue force. The results of this study highlight the ability of CIT alone to preserve muscle function during dietary restriction. Surprisingly, LEU antagonized some effects of CIT. The mechanisms involved in this antagonistic effect warrant further study.