Cardiohemodynamic effects of nipradilol (K-351) in the dog: comparison with propranolol, nadolol and prazosin.

The cardiohemodynamic effects of nipradilol (K-351) were studied in comparison with those of propranolol, nadolol and prazosin in anesthetized, open-chest dogs. All drugs were administered intravenously. Nipradilol produced dose-dependent decreases in systemic blood pressure (BP), heart rate (HR), venous return (VR) and cardiac output (COP), but virtually no change in right atrial pressure (RAP). Propranolol decreased HR, tended to decrease VR and COP and increased RAP, but produced no change in systemic BP. Nadolol also decreased HR, VR and COP and increased RAP, but did not change systemic BP. Prazosin decreased systemic BP, VR and COP and tended to decrease RAP, but scarcely affected HR. After propranolol or nadolol, nipradilol failed to reduce HR, but still produced definite decreases in systemic BP, VR and COP and a slight decrease in RAP. After prazosin, nipradilol still produced decreases in systemic BP, HR, VR and COP. These results suggest that nipradilol decreases VR and COP mainly by increasing venous capacitance through direct venodilator action and in part by increasing resistance to VR through beta-adrenoceptor blockade. This effect also appears to be responsible for its hypotensive effect.