The effects of chelating agents on the left ventricular dP/dtmax. of the paced and non-paced heart in rabbits in vivo.

The effects of i. v. administration of Na2H2EDTA and a novel chelator MgNa2EDTA (both drugs in doses of 0.05 and 0.1 mg. kg-1) on the left ventricular dP/dtmax. of the paced and non-paced heart were investigated in rabbits in vivo. Both chelators induced a decrease in cardiac contractility which was, especially after the lower doses of the drugs, significantly less pronounced after MgNa2EDTA (max. 69.6% in the non-paced and 75.2% in the paced heart) in comparison with Na2H2EDTA (max. 51.3% in the non-paced and 52.9% in the paced heart). The decrease in dP/dtmax. was similar both under the paced and non-paced heart conditions after administration of both doses of the drugs. On the basis of the results obtained, it is possible to assume that the negative inotropic effects of the new chelator MgNa2EDTA may be lower in comparison with those of Na2H2EDTA and that cardiac pacing does not influence the inotropic response to the chelators in a negative manner. Premature deaths of a number of animals after the administration of both chelators show a necessity of further studies concerning especially cardiac intracellular ion concentrations.