Time dependency of pyridostigmine-induced growth hormone response

Growth hormone (GH) plasma levels reflect a balance between stimulation via GH-releasing hormone (GHRH) and inhibition by somatostatin (SS). Steroids influence GH secretion by modulating SS tone. There is a correlation between the diurnal secretion of GH and cortisol (CORT). Pyridostigmine, the acetylcholinesterase inhibitor, increases cholinergic tone, inhibits SS release and increases the release of GH. We investigated the influence of CORT on pyridostigmine-induced GH responses by testing subjects at 9.00 and 14.00 h. Basal (mean +/- SEM) CORT levels at 9.00 and 14.00 h were 251.5 +/- 18.4 nmol/l and 142.7 +/- 6.7 nmol/l, respectively. Pyridostigmine-induced GH responses were greater at 9.00 h than at 14.00 h (8.7 +/- 1.5 mU/l; 3.0 +/- 1.0 mU/l, respectively, [ p < 0.001]). A positive correlation between CORT and delta GH values was demonstrated (p < 0.0004).