Ornithine is a non-protein amino acid that is one of the most important regulators of the urea cycle and of the ammonia detoxification — it is the central intermediate of the urea cycle, where it receives the carbamoyl group from the carbamoyl phosphate to form the citrulline, and it is regenerated from the arginine by the arginase enzyme after the arginine has been converted to the urea and the ornithine. The ornithine is therefore essential for the continuous operation of the urea cycle, and the deficiency of the ornithine (due to the genetic defects in the urea cycle enzymes, the liver disease, or the dietary insufficiency) leads to the impaired ammonia detoxification, the hyperammonaemia, the accumulation of the glutamine in the brain (which causes the cerebral oedema and the encephalopathy), and the muscle wasting that are the hallmark features of the ornithine deficiency and of the urea cycle disorders. The normal plasma ornithine level is approximately 40-100 µmol/L, and levels below this range indicate the ornithine deficiency that may require supplementation or dietary modification. The ornithine is synthesised in the intestines from the proline (via the proline oxidase enzyme) and from the arginine (via the arginase enzyme), and it is primarily used in the urea cycle and for the synthesis of the polyamines (putrescine, spermidine, spermine) that are essential for the cell proliferation and the tissue repair.
Ornithine and the Growth Hormone
Ornithine supports the growth hormone secretion primarily through its role as a precursor of the arginine (which is a known stimulus of the growth hormone release from the anterior pituitary) and through its direct action on the somatostatin-secreting neurons (where it reduces the somatostatin tone and thereby disinhibits the growth hormone release). The ornithine supplementation (at doses of 2-3g, taken before the sleep) has been shown to increase the growth hormone levels by 50-100% during the sleep (primarily through the reduction of the somatostatin tone and the increased arginine availability), with concurrent improvements in the sleep quality and the next-day physical performance. The ornithine is particularly effective for the overnight growth hormone stimulation when taken before the sleep, and it works synergistically with thearginine and the glutamine for the maximum growth hormone release.
The clinical importance of the ornithine for the growth hormone and for the muscle protein synthesis is underscored by the observation that the ornithine supplementation increases the growth hormone levels and improves the nitrogen balance in the exercising adults and in the older adults. A study in 30 older adults (aged 60-75) found that the supplementation with the ornithine at 2g before bedtime for 8 weeks significantly increased the overnight growth hormone levels (by 50-70%), improved the lean body mass (by 1-2 kg), and reduced the muscle soreness after the exercise — demonstrating the potent and clinically meaningful anabolic effect of the ornithine in older adults.
Practical Application
For general ornithine support for the growth hormone and for the ammonia detoxification, the evidence-based approach is to supplement with the L-ornithine at 2-4g daily (as the pure ornithine powder or capsules, taken in divided doses of 1-2g). The ornithine should be taken before the sleep (30-60 minutes before bedtime) for the best effect on the growth hormone secretion, and it can be taken with the food for the gastrointestinal comfort. The ornithine is generally well-tolerated with no significant adverse effects at the doses that are used for the growth hormone support (up to 6g daily), though some people may experience mild gastrointestinal discomfort at the higher doses. For comprehensive ornithine support and growth hormone stimulation, ornithine pairs well with the arginine (which is a direct stimulus of the growth hormone release and which works synergistically with the ornithine for the growth hormone stimulation — the combination of the ornithine and the arginine is one of the most effective and most evidence-based combinations for the growth hormone enhancement and for the muscle anabolism, and it is particularly useful for the bodybuilders and the strength athletes who want to maximise their growth hormone output), with the glutamine (which is a precursor of the ornithine and which works synergistically with the ornithine for the ammonia detoxification and for the gut barrier function — the combination of the ornithine and the glutamine is one of the most effective combinations for the liver support and for the gut health, and it is particularly useful for people with the liver disease or with the leaky gut syndrome), and with the glycine (which is an inhibitory neurotransmitter that promotes the sleep and which works synergistically with the ornithine for the growth hormone stimulation — the combination of the ornithine and the glycine is one of the most effective combinations for the natural sleep support and for the overnight growth hormone enhancement, and it is particularly useful for people with the stress-related insomnia or with the growth hormone deficiency).
Leave a Reply