Effects of Intravenous Endothelin on Hemodynamics and Cardiac Contractility in Conscious Milan Normotensive Rats

The effects of endothelin-1 (ET-1) on hemodynamics and cardiac contractility were compared with the responses to angiotensin I (AI) and phenylephrine (PE) in Milan normotensive rats. Intravenous (i.v.) injection of ET-1 (0.8 nmol/kg) initially decreased mean blood pressure (MBP), total peripheral resistance (TPR), and dP/dt (-28 +/- 2, -34.8 +/- 3.7, and -9.4 +/- 1.3%, p less than 0.01, respectively), and increased heart rate (HR), cardiac output (CO), and the velocity of myocardial anterior wall shortening (dL/dt) (11.8 +/- 2.1, 10.4 +/- 2.9, and 28.3 +/- 8.3% p less than 0.05, respectively). These effects were followed by a sustained increase in MBP and TPR and a decrease in CO. As compared with AI (0.25 nmol/kg) and PE (35 nmol/kg), which produced a similar degree of increase in TPR, the reduction in CO induced by ET-1 was more prominent (-25 +/- 2 by ET-1 vs. -14 +/- 2 by AI and -14 +/- 3% by PE, p less than 0.05, respectively). Moreover, ET-1 induced a significant decrease in dP/dt, shortening fraction (SF), and dL/dt (-6.1 +/- 1.6, -35.0 +/- 3.8, and -38.6 +/- 5.5%, p less than 0.01, respectively), whereas these indexes of left ventricle performance were not affected by either AI or PE. Furthermore, the reduction in SF induced by ET-1 was mainly due to the decrease in myocardial diastolic segment length, suggesting reduction in diastolic filling volume.(ABSTRACT TRUNCATED AT 250 WORDS)