Ingestion of 1.5 g of L-arginine and L-Iysine by young adults increased GH concentrations 2.7 -fold at 60 minutes post-consumption, although GH levels were not elevated 30 minutes or 90 minutes after ingestion 19 Ingestion of 1.2 g of arginine and 1.2 g of lysine by males, 15 to 20 years of age, resulted in a significant increase in GH concentrations after 30 minutes 20 Plasma GH concentration was increased nearly eightfold 90 minutes post-ingestion. The combination of 1.2 g each of arginine and lysine was more potent at stimulating GH release than either amino acid alone. Either 1.2 or 2.4 g of arginine or 1.2 mg of lysine did not increase plasma GH concentrations.These studies clearly demonstrate that arginine and lysine can induce increases in circulating GH concentrations when ingested orally.The GH response appears to be reduced in exercise-trained individuals.
Consumption of 2.4 g of arginine and lysine, or 1.85 g of ornithine and tyrosine did not induce a statistically significant increase in serum GH concentrations in young male bodybuilders over a 3-hour period, even though GH concentrations increased in five of the seven subjects. Subjects were tested in the morning following an overnight 8-hour fast. There was a large intersubject variability in GH concentrations between the subjects.
For example, 3 hours after ingestion of arginine and lysine there was a 26-fold difference in GH concentrations between the subjects with the lowest and highest GH concentrations. This may be explained in part by the pulsatile release pattern of GH. These results are consistent with observations that trained individuals have a lower GH response to various stimuli compared to untrained individuals.
Not all amino acids appear to be effective GH releasing agents. Ingestion of 10 g of aspartic acid, glutamic acid, or cysteine did not alter serum GH concentrations. Interestingly, ingestion of a mixture of branched-chain amino acids (BCAAs) immediately before 1 hour of running resulted in lower GH levels post-exercise. High serum BCAA levels may reduce synthesis of serotonin, a stimulator of GH release, in the brain.
Various factors appear to modify the GH response to amino acids and protein, including training status, sex, diet, and age. Larger amounts of amino acids may be necessary to elicit GH release in exercise-trained adults. Consumption of 170 mg of ornithine per kilogram of body weight significantly increased serum GH in male and female bodybuilders.
Nine male and three female bodybuilders ingested 40,100, and 170 mg/kg ornithine after an overnight fast on three separate occasions. These dosages are approximately 3, 7, and 12 g for a 70-kg reference man. Ninety minutes after ingestion of the 170-mg/kg dose, serum GH concentration was increased from 2.2 ng/mL at baseline to 9.2 ng/mL. Growth hormone levels were not altered significantly by the 40- or 100-mg/kg doses. However, at the highest dose all subjects experienced mild to severe stomach cramping and diarrhea.
Females show more consistent and greater overall increases in GH concentrations than men in response to arginine infusion. Intravenous administration of 183 mg/kg of arginine significantly increased plasma GH concentrations in females, age 17 to 35 years, after 60 minutes, but not in males. A dosage of 367 mg/kg, infused over a 30-minute period, was necessary for elevating GH levels in males of similar age. At dosages of 76 mg/kg and 550 mg/kg, the increase in GH concentration was substantially greater in females compared with males,
Furthermore, females showed less variability in the GH response to arginine. Ninety-seven percent of females infused with 367 mg/kg or 550 mg/kg had increases in plasma GH concentrations of 5.0 µg/mL or greater but only 56% of males had increases of 5.0 µg/mL or greater. These results are consistent with the reported increased GH release in all women, but only 20% of men, who consumed Bovril. Bovril contains 7.8 g of protein, including 438 mg of arginine and 412 mg of lysine, and has been used as a test for GH secretion. The elevation in plasma GH levels in response to arginine infusion was more than doubled in males pretreated with stilbestrol, an estrogen receptor agonist. This suggests that estrogen enhances GH release, possibly by antagonizing peripheral GH action.
The magnitude of the GH response to various stimuli, including some amino acids, may be accentuated in young subjects. Arginine infusion stimulated GH secretion in 100% of subjects aged 14 to 19 years, but in subjects 20 to 29 years of age, arginine infusion stimulated GH release in approximately 50% of the subjects 26 Ingestion of 1.5 g of arginine and 1.5 g of lysine increased GH release in approximately 50% of subjects aged 20-25 years. Administration of 3 g of arginine and lysine for 14 days did not significantly affect GH levels in elderly subjects. However, a relationship between serum GH and serum arginine was noted, suggesting that the impaired response to arginine/lysine in the elderly is due in part to decreased gastrointestinal absorption.
A diet high in protein has been reported to result in significantly greater basal GH levels compared with a normal, balanced diet. Ingestion of approximately 18 g of arginine per day for 7 days increased the sleep-related GH spike The acute GH response to amino acid ingestion may be influenced by the amount of dietary protein or amino acid supplementation. Lambert et al. and Fogelholm et al. 30 found no statistically significant effect of amino acid ingestion on GH release in male weightlifters who consumed 1.58 g/kg/day and 2.2 g/kg/day of protein, respectively.
This suggests that the use of specific amino acids to induce GH release may not be effective in strength-trained individuals consuming high-protein diets. Whether amino acids are ingested following an overnight fast or at some other time of day is likely to affect the GH response. If one were to consume a low-carbohydrate diet, the low blood glucose concentration could accentuate the effects of pharmacological or physiological stimulation of GH secretion. However, the benefits of eating small to moderate amounts of calories on a regular schedule are likely to outweigh any benefits from attempting to accentuate an amino acid or exerciseinduced GH response by fasting.