Pyridostigmine partially restores the GH responsiveness to GHRH in normal aging

In 11 elderly normal subjects and in 17 young healthy subjects we studied the response of plasma growth hormone to GH-releasing hormone (GHRH(29), 1 microgram/kg iv) alone and preceded by pyridostigmine (120 mg orally 60 min before GHRH), a cholinesterase inhibitor likely able to suppress somatostatin release. The GH response to pyridostigmine alone was also examined. Basal plasma GH levels were similar in elderly and young subjects. In the elderly, GHRH induced a GH rise (AUC, median and range: 207.5, 43.5-444.0 micrograms.l-1.h-1) which was lower (p = 0.006) than that observed in young subjects (548.0, 112.5-2313.5 micrograms.l-1.h-1). The pyridostigmine-induced GH rise in the elderly was similar to that in young subjects (300.5, 163.0-470.0 vs 265.0, 33.0-514.5 micrograms.l-1.h-1). Pyridostigmine potentiated the GH responsiveness to GHRH in both elderly (437.5, 152.0-1815.5 micrograms.l-1.h-1; p = 0.01 vs GHRH alone) and young subjects (2140.0, 681.5-4429.5 micrograms.l-1.h-1; p = 0.0001 vs GHRH alone). However, the GH response to pyridostigmine + GHRH was significantly lower (p = 0.0001) in elderly than in young subjects. In conclusion, the cholinergic enhancement by pyridostigmine is able to potentiate the blunted GH response to GHRH in elderly subjects, inducing a GH increase similar to that observed after GHRH alone in young adults. This finding suggests that an alteration of somatostatinergic tone could be involved in the reduced GH secretion in normal aging. However, a decreased GH response to combined administration of pyridostigmine and GHRH in elderly subjects suggests that other abnormalities may coexist, leading to the secretory hypoactivity of somatotropes.