Age-related blunting of growth hormone secretion during exercise may not be solely due to increased somatostatin tone

Age-related declines in growth hormone (GH) secretion may result from augme nted somatostatin (SRIH) tone and/or diminished GH-releasing hormone (GHRH) secretion. We assessed GH release during exercise without and with pyridos tigmine (PYR), which indirectly suppresses SRIH. GH levels were measured th roughout exercise and recovery in 12 young men (mean +/- SEM, 20.8 +/- 0.4 years) and seven old men (66.1 +/- 1.9), The area under the GH curve (GH-AU C) was greater in young versus old men during a short-term maximal exercise test (12.9 +/- 2.8 v 1.5 +/- 0.2 ng.min(-1).mL(-1), P = .002) and a 1-hour 60% maximal (submaximal, 10.0 +/- 1.5 v 3.0 +/- 1.0 ng.min(-1).mL(-1), P = .001) cycle exercise bout. PYR increased the GH-AUC in young and old men d uring maximal (20.9 +/- 5.2 v 4.9 +/- 1.8) and submaximal (12.3 +/- 1.6 v 4 .7 +/- 1.5) exercise (P < .05). The greater GH response to maximal versus s ubmaximal exercise suggests a role for adrenergic modulation of GHRH during exercise. However, the failure of PYR to restore the responses of the old to those of the young suggests that increased SRIH tone does not completely explain the age difference in GH secretion during exercise. Copyright (C) 1999 by W.B. Saunders Company.