Effect of surface active agents on the latent ATPase of mitochondria

Effect of inhibition of lipolysis on myocardial oxygen consumption in the presence of isoproterenol

The effect of intravenous infusion of isoproterenol on myocardial oxygen consumption (MVo(2)) was studied in 10 intact and anesthetized dogs before and after inhibition of lipolysis. In five dogs lipolysis was inhibited by nicotinic acid or beta pyridyl carbinol and in five other dogs by high plasma glucose concentrations. In spite of similar mechanical responses to isoproterenol, as evidenced by left ventricular pressure, maximal rate of rise of left ventricular pressure (dP/dt), heart rate and cardiac output, augmentation of MVo(2) was larger before (on average 7.6 ml/min.100 g) than after inhibition of lipolysis either by antilipolytic drugs (on average 4.5 ml/min.100 g) (P < 0.005), or by high plasma glucose concentrations (on average 4.3 ml/min.100 g) (P < 0.02). As mechanical responses to isoproterenol were similar before and after inhibition of lipolysis, it is concluded that the additional rise in MVo(2) with intact lipolysis was caused by a metabolic stimulation by high concentrations of free fatty acids.

Effect of free fatty acids on myocardial function and oxygen consumption in intact dogs

Myocardial function and oxygen consumption (MVO(2)) were studied during increased myocardial uptake of free fatty acids (FFA) induced by intravenous infusion of a fat emulsion (Intralipid) after heparinization in anesthetized and intact dogs. During raised myocardial uptake of FFA, MVO(2) increased in all experiments. On the average, MVO(2) rose from 8.6 to 10.7 ml/min.100 g, or 26% (P < 0.001). This was mainly due to elevated myocardial oxygen extraction, as myocardial blood flow was unchanged, or increased slightly. In the recovery period, MVO(2) returned to normal. Left ventricular pressure, the maximal rate of rise of left ventricular pressure (dP/dt), heart rate, and cardiac output remained unchanged during the raised myocardial uptake of FFA. These experiments show that increased myocardial uptake of FFA in intact hearts was associated with augmented MVO(2), despite unchanged mechanical activity.

Heart mitochondrial function in acute and in chronic hyperthyroidism in rats

The effects of acute versus chronic hyperthyroidism on rat heart mitochondria were explored. Acute, severe hyperthyroidism with an 18% loss of body weight was induced by injecting subcutaneously 10 µg/100g/day of triiodothyronine for 6 to 14 days, and chronic, anabolic, moderate hyperthyroidism was induced by placing triiodothyronine in the drinking water at a dose of 25 or 50 µg/100 ml for 15 to 60 days. Mitochondrial function was assessed polarographically using α-ketoglutarate as the oxidizing substrate, and mitochondrial structure was assessed indirectly from changes in rates of swelling in decimolar alkaline salt solutions in vitro. The P-O ratios of heart mitochondria isolated with Nagarse incubation from both types of hyperthyroid rats decreased slightly (15%) but significantly ( P = 0.05). Simple dilution of the hyperthyroid mitochondrial suspensions effected a 75% increase in the P-O ratio of the acutely treated rats but only a 19% increase in that of the chronically treated rats. Significantly increased susceptibility to swelling in vitro was exhibited only by the mitochondria of the chronically triiodothyronine-treated rats. On the other hand, only those of the acutely treated rats showed significant increases in the activity of Mg 2+ -stimulated mitochondrial ATPase. These data suggest that the mechanisms whereby excess thyroid hormone in vivo affects the function and structure of isolated rat heart mitochondria vary with the mode of induction and the duration of the hyperthyroid state.

Normal Oxidative Phosphorylation in Mitochondria from the Failing Heart

Oxidative phosphorylation was measured polarographically in mitochondria isolated from normal ventricles and from the ventricles of guinea pigs and cats with experimental heart failure produced by constriction of the aorta or pulmonary artery. The presence of heart failure was proved by the study of myocardial mechanics in vitro, by cardiac catheterization, and by postmortem examination. Mitochondria from failing ventricles had normal oxidative phosphorylation, and P-O ratios, respiratory control, oxygen consumption and ATPase activity did not differ from those of mitochondria from normal hearts. Results were the same whether incubations were performed at 25° or 37°C and whether glutamate or pyruvate and malate were used as the substrate. Mitochondria showed functional deterioration, probably due to fatty acid accumulation, when incubated for more than 10 min at 37°C or when isolated from hearts made hypoxic in vivo for as little as 3 min. The results of this study suggest that decreased myocardial contractility in experimental heart failure is not due to an intrinsic defect in mitochondrial function.