Haemodynamic rebound phenomena after abrupt cessation of propranolol therapy in portal hypertensive rats.

The haemodynamic effect of sudden termination of propranolol therapy was studied in sham-operated and portal hypertensive rats. All animals were injected with propranolol (20 mg/kg/day) or saline i.p. for 10 days, then had an isoproterenol infusion test performed 48 h or 72 h after cessation of injections. The dose of isoproterenol required to increase the heart rate by 50 beats/min (CD50), was significantly lower in both sham-operated and portal hypertensive rats at 48 h after propranolol withdrawal. Maximum chronotropic response (Rmax), was significantly higher only in portal hypertensive rats at 48 h after propranolol withdrawal. These results show the existence of a transient beta-adrenergic hypersensitivity state following propranolol withdrawal in normal and portal hypertensive rats.