Guanfacine as an alpha-2-agonist inducer of growth hormone secretion--a comparison with clonidine.

Doses of 0.5 mg and 1.0 mg of the alpha-2-adrenoceptor agonist guanfacine (GUA) and NaCl were administered intravenously (IV) in a randomized order to 18 healthy male subjects. GUA induced growth hormone (GH) secretion in a dose-dependent manner without affecting blood pressure or heart rate or inducing sedation. The effects of GUA 1.5 mg i.v. was compared with those of another alpha-2-adrenoceptor agonist, clonidine (CLON) 150 micrograms i.v. in six other male volunteers. Both alpha-2-agonists increased GH to similar levels. CLON reduced both systolic and diastolic blood pressure levels, whereas GUA reduced only systolic levels. Sedation was significantly more pronounced after CLON. The results suggest that the GUA/GH-test (1.5 mg GUA i.v.) may be an alternative to the CLON/GH-test in neuroendocrine assessment of alpha-2-adrenoceptor sensitivity.