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 metabol ism in adults. However, basal and peak GH decline with age. Exercise produc es a physiologic GH response that is subnormal in elderly people. Arginine (Arg) infusion can augment GH secretion, but the efficacy of oral Arg to im prove GH response to exercise has not been explored. We investigated whethe r oral Arg increases GH secretion in young and old people at rest and durin g 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 determi nation 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 successiv e lifts, and GH (ng . 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). O ral Arg alone did not result in any increase in GH secretion at rest 1310.8 +/- 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. Conclusion. Based upon these findings, we concluded that oral Arg does not stimulate GH secretion and may impair GH release during resistive exercise.