Oral arginine does not stimulate basal or augment exercise-induced GH secretion in either young or old adults.
BACKGROUND
Growth hormone (GH) helps maintain body composition and metabolism in adults. However, basal and peak GH decline with age. Exercise produces a physiologic GH response that is subnormal in elderly people. Arginine (Arg) infusion can augment GH secretion, but the efficacy of oral Arg to improve GH response to exercise has not been explored. We investigated whether oral Arg increases GH secretion in young and old people at rest and during exercise.


METHODS
Twenty young (Y: 22.1 +/- 0.9 y; SEM) and 8 old (O: 68.5 +/- 2.1 y) male and female subjects underwent three different trials following determination of their one-repetition maximum strength (1-RM); exercise only (EO; 3 sets, 8-10 reps at 85% of 1-RM; on 12 separate resistive lifts), Arg only (5.0 g), or Arg + exercise. Blood samples were collected between successive lifts, and GH (ng x ml(-1)) was determined via RIA.


RESULTS
In Y vs O: Basal GH secreted (area under the curve) was 543.6 +/- 84.0 vs 211.5 +/- 63.0. During EO, values were 986.6 +/- 156.6 and 517.8 +/- 85.5. Both were significantly lower in the older individuals (p < .05). Oral Arg alone did not result in any increase in GH secretion at rest (310.8 +/- 73.2 vs 262.9 +/- 141.2). When Arg was coadministered during exercise, GH release was not affected in either the young or old and appeared to be blunted in the young compared to the exercise only trial in the young.


CONCLUSIONS
Based upon these findings, we concluded that oral Arg does not stimulate GH secretion and may impair GH release during resistive exercise.
Marcell
T J
TJ
Department of Exercise Science, University of Southern California, Los Angeles, USA. marcellt@grc.nia.nih.gov
Taaffe
D R
DR
Hawkins
S A
SA
Tarpenning
K M
KM
Pyka
G
G
Kohlmeier
L
L
Wiswell
R A
RA
Marcus
R
R
D000284:Administration, Oral; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D019540:Area Under Curve; D001120:Arginine / Q000008:administration & dosage / Q000494:pharmacology*; D019587:Dietary Supplements; D015444:Exercise / Q000502:physiology*; D005260:Female; D019382:Human Growth Hormone / Q000097:blood / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D008297:Male; D011863:Radioimmunoassay
D019382:Human Growth Hormone; D001120:Arginine