Growth hormone responses to varying doses of oral arginine
Introduction
Arginine is a semi-essential amino acid that serves many purposes in the human body. Intravenous (IV) studies consistently show a large GH response when an arginine bolus is introduced [1], [2]. IV arginine administration is used clinically as a provocative test to establish GH deficiencies [2], [3], [4], and the doses used to stimulate GH release range from 2 to 40 g. Oral arginine, however, has been used primarily by the athletic population in efforts to enhance the exercise-induced GH response, yet little is known about the effects of oral arginine on GH release. Administration of oral arginine for 30 days has been shown to increase resting GH levels in postmenopausal women [5]. Acute administration of oral arginine has been reported to increase [6] or have no impact on GH secretion [7]. Previous research has administered doses ranging from 1.2 to 17 g/day [5], [6], [7], [8], and has frequently used only one sample to determine GH levels. However, no studies have examined the impact of various doses of oral arginine on the GH response. Potentially, studies administering too small of a dose of arginine may not observe a true GH response or the changes in GH levels may have been missed because of inadequate sampling. Thus, understanding the dose of oral arginine that elicits a GH response and the time course of the metabolic response after ingestion could lead to future studies investigating correct supplementation strategies and combining it with exercise. Therefore, the purpose of this study was to investigate the dose–response relationship of oral arginine on the resting GH response using frequent blood sampling, and to determine the time to the start of the GH response and the time to peak GH levels.
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Methods
Eight healthy young males (age 18–33 years) participated in this study and signed a consent approved by the Syracuse University Institutional Review Board. The mean height, weight, age, and body mass index (BMI) were 179.2 ± 2.4 cm, 78 ± 3 kg, 24.8 ± 1.2 years and 20.2 ± 0.7 kg/m2, respectively. None of the subjects were taking any medications prior to and during the study, and all subjects were non-smokers.
Each subject reported to the Human Performance Laboratory on 4 occasions (placebo, 5, 9 and 13 g day).
Results
The purpose of this study was to establish a dose response curve and a timeline after the ingested arginine elicits a GH response. For adequate absorption of oral arginine, it must be mechanically transported from the gut into the blood for a GH response to occur. Because the GH iAUC responses comprised a bimodal distribution, we categorized the subjects into those who had a GH response across provocations (responders) and those who did not (nonresponders). Two non-responders experienced GI
Discussion
Exogenous arginine administration elicits a profound GH response particularly when administered as an IV bolus (1,2,4), but a paucity of research has examined the effects of oral arginine on GH concentrations, and no studies have been conducted to establish if there is a dose response relationship. Our data indicated that 5 and 9 g of oral arginine results in a significant GH response compared to placebo, while 13 g of arginine had a substantially lesser effect. The rise in GH occurred at ∼30 min
Acknowledgement
This study was funded in part by R03AG16370-01.
References (14)
- et al.
Endocrine and lipid effects of oral L-arginine treatment in healthy postmenopausal women
J. Lab. Clin. Med.
(2000) - et al.
GH secretion by arginine stimulus: the effect of both low doses and oral arginine administered before standard test
Boll. Soc. Ital. Biol. Sper.
(1980) - et al.
Growth hormone (GH) responsiveness to combined administration of arginine and GH-releasing hormone does not vary with age in man
J. Clin. Endocrinol. Metab.
(1990) - et al.
Oral glucose tolerance test reevaluated in 68 subjects for its validity in growth hormone secretors
Boll. Soc. Ital. Biol. Sper.
(1983) - et al.
Synergy of l-arginine and growth hormone (GH)-releasing peptide-2 on GH release: influence of gender
Am. J. Physiol. Regul. Integr. Comp. Physiol.
(2000) - et al.
A study of growth hormone release in man after oral administration of amino acids
Curr. Med. Res. Opin.
(1981) - et al.
Oral arginine does not stimulate basal or augment exercise-induced GH secretion in either young or old adults
J. Gerontol. A Biol. Sci. Med. Sci.
(1999)