We investigated the effects of early chronic administration of propranolol on systemic and splanchnic hemodynamic changes, and the development of portal-systemic shunts in conscious, unrestrained, portal vein stenosed rats. Compared to rats receiving placebo, early chronic propranolol (75 mg kg-1 day-1) administration to rats begun 3 days before portal vein stenosis and then continued for 10 consecutive days, resulted in a significant decrease in both portal pressure (11.8 +/- 1.5 mmHg) and portal-systemic shunts (48 +/- 18%) which were measured 2 to 3 h after the final dose of propranolol (15.2 +/- 1.5 mmHg and 84 +/- 5%, respectively). These beneficial effects were also observed 18 to 24 h after the final dose of chronic propranolol. In rats given propranolol continuously for 5 days starting 5 days after portal vein stenosis, portal pressure (11.8 +/- 1.2 mmHg) was significantly lower than in the placebo group but portal-systemic shunts (76 +/- 14%) were not significantly different. In rats receiving a single dose of propranolol (75 mg/kg) 10 days after portal vein stenosis and measured 2 to 3 h after propranolol administration, portal pressure (12.8 +/- 1.0 mmHg) was significantly lower than in the placebo group. Portal-systemic shunts (72 +/- 17%), however, showed no significant difference from the placebo group. Similar values in portal pressure (13.3 +/- 1.2 mmHg) and portal-systemic shunts (83 +/- 21%) were also observed in rats 18 to 24 h after a single dose of propranolol.(ABSTRACT TRUNCATED AT 250 WORDS)