Trimepranol increases a negative inotropic effect of MgNa2EDTA in rabbits in vivo.

The effect of a pre-treatment with the chelator MgNa2EDTA (0.5 mg.kg-1 i.v.) on the influencing of cardiac contractility by Trimepranol (0.3 mg.kg-1 i.v.) was studied in rabbits in vivo under pentobarbital anaesthesia in the conditions of the spontaneous and paced heart rates and compared with the effects of the administration of the chelator MgNa2EDTA (0.5 mg.kg-1 i.v.) alone. The administration of the chelator alone induced especially commencing with the end of the first hour of observation, a progressive decrease in the left ventricular dP/dtmax. both in the paced heart (max. 67.0 % in the 170th min) and in the nonpaced heart conditions (max. 60.9 % in the 180th min). The administration of Trimepranol (120 min after the pre-treatment with the chelator) resulted in a pronounced increase in a negative inotropic effect (max. 43.1% in the paced and 35.3 % in the non-paced heart, always in the 130th min, i.e., 10 min after the administration of the beta-blocker), which was in most intervals significantly different from the values of dP/dtmax. after the administration of the chelator alone. A significant increase in the negative inotropic effect was manifested also by deaths of a number of experimental animals before the end of observation. On the basis of the results obtained, it is possible to assume that the combination of the administration of MgNa2EDTA with beta-blockers may especially result in an increase in the cardiodepressive action and in an occurrence of adverse effects on the hemodynamics of the organism.