The aim of the present study was to examine the short- and long-term effects of the alpha 2-agonist clonidine on sympathetic overactivity, systemic, splanchnic, and renal circulation changes, and abnormal renal sodium excretion in cirrhotic patients with ascites. Of 17 patients, 8 received clonidine and 9 a placebo. Measurements were taken before and after either a single dose of clonidine (150 micrograms) and placebo or a 1-week treatment with clonidine (150 micrograms/day) and placebo. Clonidine but not placebo induced significant short- and long-term decreases in plasma norepinephrine concentrations in the pulmonary artery and the right renal vein. Acute clonidine administration induced a significant reduction in cardiac output, heart rate, arterial pressure, and hepatic venous pressure gradient but had no effect on renal hemodynamics. Long-term clonidine administration induced a significant decrease in the hepatic venous pressure gradient from 20.1 +/- 1.9 to 17.6 +/- 2.0 mm Hg (mean +/- SEM) but had no significant effects on systemic or renal hemodynamics or renal excretion of sodium. It is concluded that long-term clonidine administration in cirrhotic patients induced a sustained decrease in sympathetic nervous activity and portal pressure. In contrast, clonidine had no prolonged effect on systemic hemodynamics. In addition, short- and long-term clonidine administration did not modify renal hemodynamics or induce a natriuretic response in patients with ascites.