[Dihydralazin versus prazosin. The hemodynamic effect of the modul substances (author's transl)]

The hemodynamic effects of dihydralazine and prazosin (0.1 and 1.0 mg/kg i.v.) on the circulatory system and left ventricular dynamics and contractility has been performed in 10 purebred beagle dogs (15.5 +- 1.4 kg) under pentobarbital sodium (35-40 mg/kg i.p.) anaesthesia by means of thermodilution and catheter technics. The changes of cardiovascular values were: 1. Either dihydralazine and prazosin decreased mean arterial blood pressure in the dose of 0.1 mg/kg i.v. Following application of 1.0 mg/kg intravenously, the arterial pressure abruptly decreased after prazosin. 2. Both pharmaca caused tachycardia. Being slowly introduced but continued by dihydralazine, the increase of pulse rate after prazosin was only initial. 3. The cardiac dynamics were differently influenced by dihydralazine and prazosin. In the estimated dose range prazosin led to an increase of cardiac output directly after application while dihydralazine induced a gradual enhancing of cardiac output. 4. The stroke volume was decreased by prazosin and slightly increased by dihydralazine. 5. While distinctly decreasing initially after prazosin, peripheral total resistance was slowly reduced by dihydralazine. 6. The contractility of the left ventricle, estimated as dp/dtmax and VCE, showed a distinct increase of the myocardial inotropy after both compounds. The maximal effect after prazosin, however, was to be seen immediately post applicationem. Dihydralazine led to a deferred enhancing of the measured contractility parameter.