CARDIAC-PERFORMANCE IN THE PORTAL VEIN-STENOSED RAT

Patient studies and experimental models suggest that impaired cardiac function might contribute to the altered pressor responses and compromised reflex responses to hypotension observed in liver disease. To elucidate the role that portosystemic shunting plays in cardiac impairment, right atrial chronotropic and right ventricular inotropic responses to a beta-adrenoceptor agonist were compared using isolated cardiac tissues from sham-operated and chronic portal vein-stenosed rats. Maximal chronotropic responses of sinoatrial tissue from portal vein-stenosed rats to isoproterenol were reduced 18% (P < 0.05) with no change in sensitivity [mean effective dose (ED50)]. Basal indexes of contraction were diminished 48% (P < 0.0025) and 60% (P < 0.0005) for developed tension and change in force over change in time (dF/dt), respectively, in ventricular tissue from portal vein-stenosed animals. In addition, the maximal response for isoproterenol-induced ventricular contraction was smaller in portal hypertensive animals (-44%, P < 0.0005, and -52%, P < 0.01 for developed tension and dF/dt, respectively), but no changes in isoproterenol ED50 values were found. These results indicate that portal venous hypertension with extensive portosystemic shunting leads to impairment of basal myocardial contraction and decreased chronotropic and inotropic responsiveness to beta-adrenoceptor agonists.