Lack of effect of muscarinic cholinergic blockade on the GH responses to GRF 1-29 and TRH in acromegalic subjects.

It is well known that muscarinic cholinergic blockade either reduces or abolishes stimulated GH release in normal subjects. In this study we have investigated whether cholinergic muscarinic blockade could reduce the GH responses to GRF 1-29 and TRH in acromegalic subjects. Eight acromegalic subjects underwent two GRF tests (GRF 1-29, 1 microgram/kg i.v.) with and without pirenzepine (0.6 mg/kg, i.v.). A further four of these patients received TRH (200 micrograms/kg, i.v.) on separate occasions with and without pirenzepine (0.6 mg/kg, i.v.). Cholinergic muscarinic blockade did not alter the GH responses to GRF and TRH in patients with acromegaly. These findings are in contrast with previous data reported on the effects of cholinergic blockade on stimulated GH levels in normal subjects and in patients with type I diabetes mellitus and are compatible with the view that somatotroph adenomas are functionally disconnected from hypothalamic control mechanisms.