Effect of methysergide and pimozide on apomorphine-induced growth hormone secretion in men

The dopamine receptor agonist, apomorphine HCl (0.75 mg sc) increased serum growth hormone (GH) concentrations in each of 6 subjects. This increase was not inhibited by pretreatment with the serotonin antagonist, methysergide, but was completely abolished in the 4 individuals pretreated with pimozide, a selective dopamine receptor blocking agent. These results provide further evidence that apomorphine-induced GH secretion is mediated by a dopaminergic mechanism and is independent of a serotonergic mechanism.