Supplementation Amino acids and creatine

Citrulline: functions and contraindications

Citrulline: functions and contraindications

by in Supplementation - Amino acids and creatine

last updated: November 28, 2016

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Citrulline is an amino acid that isn't just used in the sports field. It has a range of functions including: increasing arginine levels in the blood, and vasodilation, via the synthesis of nitric oxide

What is citrulline?

Citrulline (C6H13N3O3) is a non-essential amino acid (we can synthesise it ourselves), which was isolated for the first time from watermelons via the action of calcium-dependent enzymes called peptidyl-argininedeamidases.

Citrulline exerts its action primarily in the liver, where, starting from arginine, nitrogen monoxide is formed as a result of enzyme-catalysed reactions, a by-product of which is citrulline.

This amino acid is, as well as being 'one of its by-products' is a precursor of' l-arginine and a derivative of ornithine to which it binds via a carbamate residue.

Via these processes, citrulline enters the metabolic pathway of urea, which takes place in the liver (urea cycle), where it functions as an intermediary. This process is essential to the human body for the elimination of nitrogenous (urea), starting with ammonia, a substance that is toxic for our body, and whose accumulation leads to both a reduction in muscle glycogen formation and the early onset of fatigue (aerobic or anaerobic activity increases its production).

Here is an equation summarising the pathway:

Ornithine + carbon monoxide + ammonium → citrulline + aspartic acid → arginosuccinico acid → arginine

Functions of citrulline:

1. Increased arginine

Integration of L-Citrulline has been shown to be useful for increasing the levels of arginine (as well as of citrulline) in the blood, available for the synthesis of nitric oxide. as well as for the other functions it is associated with. Studies have shown that with the same dose and method of administration (oral), citrulline would induce an increase in blood arginine levels almost twice as high as the same dose of slow-release arginine, and even some 20% higher than the same dose of immediate release arginine.

2. Vasodilation

When arginine, by increased availability, is converted into nitric oxide, it induces a vasodilatory effect by stimulating the cardiovascular system, and improves the reflex elasticity of blood vessels.

The vasodilation induced by nitric oxide is used by doctors to treat mild erectile dysfunction, and by athletes to enhance their performance by increasing the blood supply, so more oxygen and nutrients are delivered to the tissues involved in the work (increases the metabolic rate of the body).

3. Recovery from physical and psychological stress

4. Anti-atherosclerotic

5. Protection of blood vessels

6. Citrulline "malate" and enhancement of aerobic performance

L-citrulline is often salified with malic acid to produce citrulline "malate" (also other salts of arginine but not as much; known and used as c.malate) with the aim of increasing the ergogenic effect.

Citrulline malate in the body leads to an increase in the levels of bicarbonate, an acid that, via its buffering function, absorbs molecules of lactic acid. One study (French) indicated that taking citrulline malate prior to an aerobic exercise resulted in a significant reduction in the feeling of fatigue and an increase of 34% in ATP production during these activities, in addition is an increase of 20% in PCR recovery afterwards.

The dose for the ergogenic effects of citrulline malate is at least 6 grams (typically 8).

Athletes in high intensity sports with a predominance of aerobic operations, like boxers, football players, basketball players, runners, cyclists, etc., can benefit greatly from integration of citrulline malate.

Contraindications and other information:

  1. When there is a shortage of the'enzyme required to catalyse the citrulline-arginine urea cycle, a disease called citrullinemia may develop, that leads to ammonia formation in the blood. Research indicates that supplementation with zinc can improve the conversion of citrulline - arginine in the liver and at the same time keep the levels of NH3 in the blood low.

  2. This amino acid, promotes the use of three essential branched chain amino acids (BCAA: Valine, Leucine, Isoleucine) as an energy source, reducing serum concentrations during prolonged exercise.

  3. Dosage and mode of application:
    Citrulline malate is recommended at a starting dose of 6 grams, and after evaluating the effects (too high doses can cause nausea and abdominal pain) increasing this to 8.
    Citrulline must be taken about 15-30 minutes before training, or even intra-workout to have a more diluted action across the entire workout.

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