Pyridostigmine potentiates growth hormone (GH)-releasing hormone-induced GH release in both men and women

It has been recently reported that pyridostigmine (PD), an indirect cholinergic agonist, probably acting via inhibition of hypothalamic somatostatin, potentiates the GH-releasing hormone (GHRH)-induced GH rise in men, but not in women. The aim of this study was to verify the sex-related, if any, GH response to GHRH (1 μg/kg, iv, as a bolus) both alone and preceded by two different doses of PD (120 mg, group A, and 60 mg, group B, given orally 60 min before GHRH) in a large group of volunteers (36 women, aged 18-35 yr, and 48 men, aged 18-35 yrs). In group A, 120 mg oral PD potentiated the GH response to GHRH in both men [area under the curve (AUC), 2579.3 ± 264.5 vs. 806.2 ± 99.7 μg/L*h; P <0.00001] and women (AUC, 2273.2 ± 248.7 vs. 792.6 ± 72.7 μg/L*h; P <0.00001). Similarly, in the group B, 60 mg oral PD potentiated the GH response to GHRH in both men (AUC, 1929.6 ± 157.2 vs. 568.2 ± 81.3 μg/L*h; P<0.01) and in women (AUC, 1655.9 ± 146.9 vs. 738.2 ± 105.7 μg/L*h; P <0.01). The GH responses to GHRH, both alone and after 120 and 60 mg oral PD, did not significantly differ in men and women. No sex-related difference was observed in the cholinergic side-effects (mild abdominal pain and muscle fasciculations) that occurred in nearly 30% of the subjects. In conclusion, our results clearly show that there is no sex-related difference in the potentiating effect of PD on GHRH-induced GH release, ruling out the suggestion that women have increased cholinergic activity, leading to reduced somatostatinergic tone.