Amino Acids and the Effect on GH levels

When subjects experienced with weight-training exercises performed a workout lasting approximately 45 minutes, GH levels were dramatically elevated during the workout and remained higher for approximately 70 minutes post­exercise. Subjects performed 3 sets to voluntary exhaustion at 70% of their 1-RM for seven different exercises. Although GH concentrations were increased 2.7 fold 60 minutes after consumption of 1.5 g of arginine plus 1.5 g of ornithine, ingestion of arginine and lysine before the workout did not result in greater increases in GH concentrations than exercise alone. Blood GH concentration was elevated in four male throwers 2 hours after a weight-training circuit, which was performed following an overnight fast. Consumption of an amino acid combination of 1.8 g of L-arginine, 1.2 g of L-ornithine, 0.48 g of L-methionine, and 0.12 g of L-phenylalanine did not alter GH concentration during the workout compared with exercise alone.

A protein supplement ingested immediately before exercise and 2 hours after resistance­training exercise had no effect on post-exercise changes in GH concentrations. Exercise is a potent stimulus for GH release and amino acids may not further augment GH release during or after exercise. Administration of 20 g of arginine and glutamate to highly trained cyclists approximately 2 hours before cycling at 75-83% of maximal aerobic power for 60 minutes greatly reduced the rise in plasma GH concentration. In the placebo condition, GH levels peaked after 30 minutes of exercise before beginning to decline, but were still significantly elevated 30 minutes post-exercise. Ingestion of arginine and glutamate significantly decreased the exercise-induced rise in GH. The blunted GH response to arginine-glutamate may be due to the highly trained status of the cyclists, or more likely that glutamate reduces the GH stimulatory effect of exercise.

The effects of consumption of 6 g of amino acids daily for 4 days on GH release was examined in highly trained weightlifters One gram each of arginine, lysine, and ornithine were consumed at 1 PM and again at 9 PM daily. Subjects also performed a 90-minute weight -training session with resistances of 70-80% of maximal load beginning at 1 PM. The pattern and magnitude of GH secretion over a 24-hour period was not different between placebo and amino acid-supplemented conditions. Subjects in this study consumed high-protein diets of 2.2 g/kg/day (19% of total energy intake). This might mask or blunt a possible effect of amino acids on GH secretion.

Amino acid supplementation did not affect GH concentrations before or after 7 days of high-volume weightlifting in elite junior weightlifters Although this study is sometimes cited as showing that amino acids do not alter GH release, the purpose of this study was not to examine the effects of amino acids as growth hormone releasing agents. Furthermore, the total amount of arginine, ornithine, and lysine ingested was only 2082 mg daily. An amino acid supplement of 2.368 g was consumed before each of three daily meals and included 694 mg of arginine, ornithine, and lysine. Also, 2.1 g of branched­chain amino acids and 50 mg of glutamine were consumed before each workout. Consumption of branched­chain amino acids or glutamine may reduce the GH response to exercise.

It has been suggested that failure to find an enhancement of the acute GH response to exercise when arginine and lysine were ingested immediately before exercise may be related to a reduction in gastrointestinal tract blood flow. During exercise, blood flow is directed away from the gastrointestinal tract toward active muscles. Thus, absorption of arginine and lysine could be attenuated. A relationship between blood amino acid and GH levels has been reported in the elderly. However, infusion of 30 g of arginine, 20 minutes after the completion of 20 minutes of brisk walking, was not effective in increasing the GH response to exercise. Arginine infusion was used to bypass absorption issues. Larger doses taken orally of arginine and lysine could be given in conjunction with exercise to enhance the acute GH response to exercise. However, large doses may exceed bowel tolerance and cause intestinal disturbances.

The anabolic effects of GH are mediated by insulin­like growth factor-1, therefore, the timing of amino acid ingestion to elevate GH and IGF-1 levels is uncertain. Increases in somatomedin A, an earlier designation for IGF, were not detected when blood was sampled from 30 minutes to 2 hours after administration of 1.2 g each of arginine and lysine. However, somatomedin-A levels were elevated threefold at the 8-hour time point. Additional studies are needed to assess both the GH and IGF-1 response to amino acids and exercise.

By Steve Mathew