Guanfacine in essential hypertension: effects during rest and isometric exercise

The antihypertensive effects of guanfacine (0.5 to 4 mg daily) were investigated for 1 yr in 13 patients with essential hypertension. Blood pressure (BP) and heart rate (HR) response was measured during isometric exercise (handgrip) before starting the therapy, after 1 yr of treatment, and 2 wk after withdrawal. Guanfacine in once-daily dosage reduced BP during rest (supine BP: control, 175 +/- 6/103 +/- 4 mm Hg; 1 yr guanfacine, 161 +/- 5/91 +/- 3 mm Hg). Steady-state plasma concentrations after 1 yr were 4.1 +/- 0.59 ng/ml. Resting plasma norepinephrine (NE) and epinephrine (E) levels were lower during active therapy than 2 wk after withdrawal (guanfacine and control: plasma NE, 0.27 +/- 0.03/0.64 +/- 0.13 ng/ml; plasma E, 0.09 +/- 0.02/0.17 +/- 0.05 ng/ml). The relative reduction of plasma catecholamines (guanfacine and withdrawal) was of the same order during handgrip exercise as during supine rest. During isometric handgrip exercise, BP was lower during guanfacine therapy than before treatment and 2 wk after withdrawal, but the increment in BP during handgrip exercise was not affected by the drug despite the lower BP values on therapy. Our data indicate that the central alpha 2-agonist action of guanfacine reduces sympathoadrenal function equally during rest and isometric exercise.