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In this paper, an attempt was made to describe the alterations of the myocardial energy metabolism following moderate stenoses of aorta or pulmonary artery. Biochemical investigations regarding the main high energy phosphates and a large series of dehydrogenases in the myocardium of the overloaded ventricles have revealed the following facts: (1) the myocardial CP-CPK system appears to be more labile than the myocardial AMP-ATP system in response to a ventricular overload; (2) the changes in the amounts of myocardial high energy phosphates seem to be more important in the right chronic cardiac overload than in the left one; (3) before the overloaded ventricle becomes insufficient, the myocardial dehydrogenase system elicits no alteration, suggesting that the oxidative phosphorylation is not affected; (4) there is a closer relationship between the coronary flow and pressure and the myocardial energy metabolism than that existing between this metabolism and the tension of the myocardial fibres following a persistent increase in the systemic arterial resistance.

Myocardial adenine nucleotides (nicotinamide adenine nucleotides included), glutathione, catecholamines (DOPA, dopamine, noradrenaline, adrenaline) and some enzymes in correlation were investigated in dogs with cardiac failure induced by bilateral iliac arteriovenous fistulas, and unilateral (left) heart vagotomy was also studied for its influence on the changes in the myocardial amounts of these compounds occuring in this pathological circumstance. The cardiac failure in arteriovenous fistula was characterized by the following myocardial metabolic aspects: (I) no change in the amount of proteins (although an important cardiac hypertrophy was present); (II) decreases in the amounts of adenine nucleotides (especially ADP and ATP), without significant variations in the adenosine concentration, accompanied by increases in the concentrations of nicotinamide adenine nucleotides (in both their oxidized and reduced forms) in the heart mitochondria; (III) no change in the amounts of oxidized and reduced glutathione and in the activity of NADH2-dependent glutathione reductase; (IV) a very significant increase in the activity of MAO without significant influences on the levels of the studied catecholamines. The partial vagal denervation of the heart was found to attenuate substantially the changes in the amounts of adenine nucleotides and nicotinamide adenine nucleotides in the myocardial mitochondria and to facilitate the action of MAO on noradrenaline leading to a significant decrease in its myocardial level.

An approach to explain the early metabolic disturbances induced by a moderate ischaemia on the basis of comparative biochemical investigations concerning the oxidative metabolism in the skeletal muscles, is the object of the present paper. These investigations have revealed the following findings: (i) during a slight ischaemia the skeletal muscle maintains its ability to oxidize in vitro lactate and exhibits an increased activity in oxidizing pyruvate, succinate and L-glutamate, and (ii) the stores of adenosine and ATP are depleted and an important accumulation of inorganic phosphate, accompanied by a remarkable activation of phosphatases, occurs in the ischaemic muscle, while no significant changes in the ATPase and creatine phosphokinase activities and in the amount of AMP, ADP and creatine phosphate are detectable in this muscle.

Investigations regarding the metabolism of proteins and electrolytes in the hindlimb skeletal muscles were carried out in dogs with a moderate unilateral stenosis of femoral artery (reduction of almost 65% of its lumen) early after surgery. The results of these investigations were compared with those obtained by investigating the correspondent skeletal muscles of the opposite hindlimb. This comparison has revealed the following findings: (1) ischemia in a moderate form early elicites a remarkable K+ accumulation (not a K+ loss!) in the skeletal muscle without any change in the concentrations of other cations; (2) in this instance, an activation of muscle proteases and peptidases occurs meading to an important production of histamine, which is detectable in appreciable amounts in the ischemic muscle and, especially, in its effluent blood. On the basis of the findings reported in this study, as well as on the basis of our previous findings on the same experimental model, an approach to correlate and explain the early muscular metabolic disturbances induced by a moderate ischemia is discussed. In addition, it is to be pointed out that the presence of histamine in increased amounts in the effluent blood of a skeletal muscle mass could be a reliable laboratory parameter revealing an incipient muscle ischemia.