Effects of Pimozide and Metergoline on Clonidine- stimulated growth hormone secretion in patients with essential hypertension

The aim of the present study was to determine: (1) whether the single maximal dose of clonidine, an alpha2-adrenergic agonist, could induce an increase in serum growth hormone (GH) levels in patients with essential hypertension, and (2) whether hypotalamic dopamine and serotonin receptors might be involved in this response. Sixteen patients were studied before and after a 4-day treatment with a selective dopamine-blocking agent, pimozide. Another group of eight hypertensives was studied before and after a 5- day treatment with a specific blocker of serotonin receptors, metergoline. Total clonidine-stimulated GH secretion was assessed by the area under the GH curves from 0 to 180 min. The single maximal dose of clonidine induced in the majority of patients a moderate increase in GH levels, still indicating a subsensitivity in central alpha-adrenergic function in human hypertension. Both pimozide and metergoline failed to change the total secretion as well as the pattern of GH response to clonidine, irrespective of the magnitude of individual responses. In conclusion, the results of this study demonstrate that neither dopaminergic nor serotonergic mechanisms are involved in the alpha2-adrenergic control of GH secretion in patients with essential hypertension.