Propranolol prevents hemodynamic and humoral events after abrupt withdrawal of nitroprusside

Hemodynamic and humoral events after intraoperative discontinuation of nitroprusside were studied in subjects without and with pretreatment with intravenous propranolol, 0.1 mg X kg-1. Nitroprusside-induced hypotension was associated with increases in heart rate, cardiac output, plasma renin activity (PRA), and catecholamine levels; these changes were prevented by propranolol. In subjects pretreated with propranolol, dose requirements of nitroprusside for hypotension of comparable degree and duration decreased 40%. On discontinuation of nitroprusside, mean systemic pressure rose to 100.2 mm Hg--a level higher than prehypotension and awake values--because of increased systemic vascular resistance. Hemodynamic events were associated with persistent elevations of PRA and catecholamine levels. These rebound changes were maximal 15 min after nitroprusside withdrawal and returned to control levels 30 to 60 min later. Pretreatment with propranolol completely prevented rebound hemodynamic events after nitroprusside. Persistent elevations of PRA and catecholamine levels after nitroprusside action subsided were responsible for the effects of withdrawal.