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.