Comparison of the cardiovascular effects of phentolamine, sodium nitroprusside and nitroglycerin in anaesthetized cats (comparison of vasodilators).

The effects of phentolamine (PH), sodium nitroprusside (NP) and nitroglycerin (GTN) were compared in experiments on anaesthetized cats. All three agents diminished vascular resistance and lowered blood pressure, although they differed in the intensity of their effects (NP greater than PH = GTN) and in the steepness of their dose-response curves (NP greater than PH greater than GTN). NP and GTN did not cause consistent changes in heart rate and dP/dt, whereas PH produced marked, dose-dependent increases in these two variables and in cardiac output, which was augmented to a lesser extent by NP and not affected by GTN. It is concluded that whereas the beneficial therapeutic effects of NP and GTN are presumably due exclusively to the reduction of preload and afterload, PH has an additional cardiostimulant action.