Growth hormone responses to varying doses of oral arginine

Intravenous (IV) arginine invokes an increase in growth hormone (GH) concentrations, however, little is known about the impact of oral arginine ingestion on the GH response. Objective: The purpose of this study was to determine the dose of oral arginine that elicits an optimal GH response and to determine the time course of the response. Design: Eight healthy males (18-33 years - 24.8 ± 1.2 years) were studied on 4 separate occasions. Following an overnight fast at 0700 h, a catheter was placed in a forearm vein. Blood samples were taken every 10 min for 5 h. Thirty minutes after sampling was initiated, the subject ingested a dose of arginine (5, 9 or 13 g) or placebo (randomly assigned). Results: Mean resting GH values for the placebo, 5, 9 and 13 g day were 0.76, 0.67, 2.0 and 0.79 μg/L (n = 6), respectively. Integrated area under the curve was not different with 13 g (197.8 ± 65.7 min μg/L), yet it increased with 5 and 9 g compared with the placebo (301.5 ± 74.6, 524.28 ± 82.9 and 186.04 ± 47.8 min μg/L, respectively, P < 0.05). Mean peak GH levels were 2.9 ± 0.69, 3.9 ± 0.85, 6.4 ± 1.3 and 4.73 ± 1.27 μg/L on each day for the placebo, 5, 9 and 13 g days. Conclusion: In conclusion, 5 and 9 g of oral arginine caused a significant GH response. A 13 g dose of arginine resulted in considerable gastrointestinal distress in most subjects without augmentation in the GH response. The rise in GH concentration started ∼30 min after ingestion and peaked ∼60 min post ingestion.