Activity of Na+/K+-ATPase and of Ca++-ATPase under the action of adenosine triphosphate in experimental myocardial hypertrophy.

This paper presents the results of our research on the mechanisms involved in the modifications occurring in the activity of ionic pumps (Na+/K+-ATPase and Ca++-ATPase) at the level of the sarcolemma, the sarcoplasmic reticulum and mitochondrial membrane of the myocardial cell in experimental myocardial hypertrophy induced by isoproterenol. We also studied the effects of concomitant administration of adenosine triphosphate. Thus, we found the activity of the sarcolemmal Ca++-ATPase intensely increased under the action of isoproterenol, while Ca++-ATPase activity in the sarcoplasmic reticulum decreased significantly. At the same time, the Na+/K+-ATPase activity decreased both in the sarcolemma and in the sarcoplasmic reticulum. Administration of adenosine triphosphate induces opposite effects, of lower intensity, upon the activity of the two ATPase, that tend to offset the the effects of isoproterenol. This was found in the group of rats given concomitantly both isoproterenol and adenosine triphosphate. A better understanding of the processes involved in those modifications of membrane ATPase activity allows us to consider their different behaviour to isoproterenol and adenosine triphosphate as the expression of intrinsic mechanisms by means of which the myocardial cell intervenes in maintaining a physiological concentration of calcium ions (Ca++) that is necessary both in order to avoid a failure of the contractile apparatus and in order to preserve the mitochondria role of ATP supplier. Our results demonstrate the antiadrenergic action of adenosine triphosphate that attenuates isoproterenol effects on cardiac myocytes.

Research on some metabolic and enzymatic modifications in experimental hypertensive myocardium.

This paper presents our research on metabolic and enzymatic changes in the experimental, Isoproterenol-induced (ISO) hypertensive myocardium of rats. We analyze the effects produced by the simultaneous administration of adenosinetriphosphate (fosfobion) (FOS) and Isoproterenol on the changes in the body weight/heart weight ratio, and on the biochemical changes of cardiac metabolism. We studied the following parameters in the myocardium tissue and blood: plasmatic and tissular creatinin-phosphokinase, Na+K+ ATP-ase in the sarcolemma and the sarcoplasmic reticulum, Ca+2 ATP-ase in the mitochondrial membrane, sarcoplasmic reticulum and sarcolemma, as well as plasmatic and tissular lactate. Our data show an increase of heart weight to 939 mg, compared to 752 mg in the control group, while the heart weight/body weight ratio (mg/g), which was 3.8 in the control group, increased to 5.8 in the group to which Isoproterenol (ISO) was administered, and to 5.2 when fosfobion was associated. Investigation of myocardial metabolism has also shown the fact that under the influence of Isoproterenol, plasma creatinin-phosphokinase rises by 20%, while the association of fosfobion reduces it, in the myocardium tissue, down to 73%, in comparison with the values in the control group. Significant changes were found in the myocardium lactate that decreased by 26% under ISO influence, in comparison with normal values, and that decreased by 90% when FOS and ISO were administered together. This study produces arguments about metabolism-induced cardiac changes under the action of ISO and also contributes to the identification of ways that lead to cardiac hypertrophy. The experiment also demonstrates that the ATP-ases responsible for ion transportation across the membrane are actively involved in myocardium hypertrophy. The disturbances occurring in the investigated enzymatic systems are closed related with the myocardial metabolic ones. Fosfobion does not prevent the appearance and development of Isoproterenol-induced myocardial hypertrophy, but diminishes the increase of myocardial lactate produced by this synthesised catecholamine. At the same time, fosfobion significantly decreases the activity of Ca+2 ATP-ase in the plasmalemma and increases the activity of the Na+ - K+ ATP-ase both in the plasmalemma and in the sarcoplasmic reticulum, indirectly favouring the mechanical processes of cardiac myocytes relaxation. The study of the enzymatic activity of Na+K+ and Ca+2 ATP-ases in our experimental conditions contributes to a better understanding of the mechanisms that produce myocardial and coronary disturbances in myocardial hypertrophy.