Effects of 2,3,7,8-tetrachlorodibenzo- rho -dioxin treatment on mechanical function of the rat heart

Mechanical responses of isolated atria to (-)-isoproterenol and activities of myocardial pyruvate kinase and citrate synthase, enzymes involved in energy metabolism, were assessed in rats 7 days after 2,3,7,8-tetrachlorodibenzo- rho -dioxin (TCDD) treatment. Basal tension development by electrically paced left atria was significantly elevated by all doses of TCDD (6.25, 25, or 100 mu g/kg) when compared to that of vehicle-treated rats with unlimited access to feed. The basal rate of spontaneously beating right atria was significantly depressed in rats receiving 100 mu g/kg TCDD. In left atria from rats treated with 100 mu g/kg TCDD, maximal inotropic responses to (-)-isoproterenol and 1-methyl-3-isobutylxanthine were enhanced to the same degree. Right and left atria from rats receiving 100 mu g/kg TCDD had an increased sensitivity to the chronotropic and inotropic effects of (-)-isoproterenol, respectively.