[Effects of prazosin, SGB-1534, dobutamine and isoproterenol on congestive heart failure in dogs].

Effects of prazosin, dobutamine, isoproterenol and SGB-1534, a new alpha-blockade, on congestive heart failure (CHF) in dogs were investigated. The model was made by protease injection into the left ventricular free wall, saline loading, and dextran and methoxamine infusions. By this maneuver, left atrial pressure (LAP), systemic vascular resistance (SVR) and left ventricular end-diastolic pressure (LVEDP) were markedly increased, aortic blood flow (AoBF) was decreased, and systemic blood pressure was unchanged. In this model, the intravenous administration of prazosin (0.1 approximately 10.0 micrograms/kg, i.v.) increased AoBF and decreased LAP in a dose-dependent manner. The improvement of the CHF by prazosin was considered to result from its vasodilating action. SGB-1534 (0.1 approximately 10.0 micrograms/kg, i.v.) improved the CHF mainly through its vasodilating and positive inotropic actions, which is because SGB-1534 decreased SVR and increased Vmax. The magnitudes of vasodilation by SGB-1534 was greater than those by prazosin. These data indicate that SGB-1534 is useful in the treatment of CHF. Both dobutamine (5 approximately 100 micrograms/kg, i.v.) and isoproterenol (0.001 approximately 0.1 micrograms/kg, i.v.) improved the CHF through their vasodilating and positive inotropic actions in the canine CHF. The ratio of positive inotropism/vasodilation was greater for dobutamine than isoproterenol. The vasoconstriction by the large dose of dobutamine might participate in this difference between dobutamine and isoproterenol.