Inhibitory effect of an ergoline derivative, methergoline, on growth hormone and prolactin levels in acromegalic patients.

Plasma levels of growth hormone (GH) and prolactin (PRL) were measured in twelve acromegalic patients after acute administration of an ergoline derivative (methergoline) which has been proposed as a specific serotoninergic blocking agent. The administration of methergoline (4 mg p.o.) was followed by a significant decrease in plasma GH and PRL concentrations. The administration to the same subjects of CB 154 (2.5 mg p.o.), a known stimulator of dopaminergic receptors, led to results almost superimposable to those obtained with methergoline although the suppressive effect of CB 154 on GH and PRL levels was more sustained. Also on the ground of results obtained in these patients with the use of cyproheptadine, phentolamine, or pimozide, we have concluded that methergoline inhibition of GH and PRL release is, in acromegalic patients, most probably due to a dopaminergic mechanism of action.