Effects of subchronic lead intoxication on the myocardium contractility of rats

While it is known that chronic lead intoxication in humans induces arterial hypertension and thus can lead to some secondary disturbances of heart function, possible effects of this intoxication on myocardium contractility has never been proved. In our experiments outbred male rats were repeatedly injected IP with sub-lethal doses of lead acetate 3 times a week during 5 weeks. They developed an explicit even if moderate lead intoxication characterized by typical hematological and some other features. Next day after the last injection the heart of each animal was excised, and trabecules and papillary muscles from right ventricle were used for modeling in vitro isometric regimes of contraction-relaxation cycle. Several well-established parameters of this model proved to be changed as compared with preparations taken from hearts of healthy control rats. Against the background of in vivocalcium treatment both systemic and cardiotoxic effects of lead were somewhat attenuated. For the first time we showed that at subchronic intoxication with lead the myocardial preparations in a wide range of lengths react with decrease in their time and speed parameters of isometric contraction while keeping its amplitude, and with decrease in the passive stiffness of the trabecules. Features of the reaction of different structures of the heart and the shifting of isomyosin ratio to the slow isoform were demonstrated. Mechanistic and toxicological inferences from the results obtained are discussed.