Effects of mercury on the contractile activity of the right ventricular myocardium

The increase in right ventricular systolic pressure observed in vivo after the administration of mercury opposes to the idea that the metal depresses the cardiac pump performance. We then investigated the effects of HgCl2 (0. 1 to 2.5 VM) on the contractile activity of the right ventricular myocardiu m, measuring isometric and tetanic contractions of right ventricular isolat ed strips, right ventricular isovolumic systolic and diastolic pressures, a nd the coronary perfusion pressure (0.03 to 3 muM) in constant-flow Langend orff-perfused rat hearts. The results presented here suggest that the acute effects of mercury on the right ventricular myocardium are distinct. When isolated strips of right ventricular wall are used, the contractile depress ion produced by mercury is manifested. However, when mercury is administere d to isolated perfused hearts or in vivo this depressant effect is not reve aled. The possible reasons for this behavior are the increased coronary per fusion pressure, which promotes a positive inotropic effect, manifested dur ing the infusion of increasing concentrations of mercury, or the putative s tretch of the ventricular fibers, which might cause the increment of diasto lic pressure. An interesting finding is that the mechanical activity of the preparations, in which mercury is administered via coronary circulation, i s not depressed and, even more, it can increase systolic pressure. However, the nature of this protective effect of coronary circulation cannot be exp lained by the results presented here.