[The effect of endothelin on the hemodynamics and cardiac contractility in waking rats with normal and artificially elevated levels of atriopeptide in the blood].

The effects of endothelin (0.1 nMol/kg and 1 nMol/kg into the left ventricle) on hemodynamics and cardiac contractility were investigated in conscious and unrestrained, WKY rats before and during continuous infusion of atriopeptides (1 microgram/kg/min i.v.). Bolus injection on endothelin into the left ventricle caused a transient hypotension and tachycardia followed by a long-lasting increase in mean blood pressure (MBP) and bradycardia in intact rats. In the rats receiving constant atriopeptide infusions, the hypotensive phase of endothelin effects was augmented whereas the hypertensive phase was reduced. Endothelin doses dependently increased cardiac contractility parameters during the first 3 minutes after injection. The stimulation of cardiac function at this time resulted from reflex responses due to the rapid decrease in the MBP. These effects were followed by decreases in cardiac contractility indices. Infusion of atriopeptide led to a tendency to the positive inotropic action of and augmented the negative inotropic action of endothelin.