Growth hormone, noradrenaline, blood pressure and cortisol responses to clonidine in healthy male volunteers: dose-response relations and reproducibility.

The growth hormone (GH) response to clonidine (CLON) has been investigated to date mostly with CLON doses of 2.0 micrograms/kg or 150 micrograms intravenously (IV). The present study investigated GH and blood pressure (BP) responses to CLON (2.0 and 1.5 micrograms/kg IV) (Study I). Twelve healthy male volunteers were tested with the two CLON doses and saline in a cross-randomized design. Plasma GH, noradrenaline (NA) and cortisol concentrations, BP and sedation were determined. CLON (1.5 and 2.0 micrograms/kg) induced a significant dose-dependent GH increase, but only the 2.0 micrograms/kg dose differentiated GH responders from nonresponders. In contrast to GH, NA, cortisol, and BP did not differ significantly after either CLON dose. We also studied GH responses to repeated CLON stimulation (Study II). Ten healthy male volunteers were given four CLON tests (2.0 micrograms/kg) at three-week intervals. The nine volunteers who participated in both studies were investigated over a time course up to 21 months. The subjects could be classified into those who showed consistent GH responses greater than 5 ng/ml, those who showed consistent GH responses less than 5 ng/ml, and those who showed both degrees of responses.