Effect of Enhancement of Endogenous Cholinergic Tone with Pyridostigmine on the Dose-Response Relationships of Growth Hormone (GH)-Releasing Hormone-Induced GH Secretion in Normal Subjects*

It is well known that GH responses to GHreleasing hormone (GHRH) show marked interindividual variations in normal subjects, which have been attributed to a variable somatostatinergic tone. Recently, it has been shown that enhancement of cholinergic tone with the acetylcholinesterase inhibitor pyridostigmine (PD), which presumably acts by inhibiting somatostatin release, stimulates basal GH secretion and GH responses to a maximal dose of GHRH. In this study we have investigated the effects of PD on the dose-response relationships of GHRH-induced GH secretion in normal subjects. Our data showed that PD (120 mg, orally, at −60 min) induced a clear-cut increase in basal GH levels, significantly different from that after saline treatment, at 15, 30, 45, 60, 90, and 120 min. Moreover, PD administration markedly potentiated GH responses to GHRH at doses of 500, 100, 25, 10, and 3 μg/subject, as assessed by either area under the curve or maximal peak GH levels. In fact, GH responses to pyridostigmine plus 3 ng GH...