Effect of in vivo propranolol treatment on oxidative energy metabolism in rat liver and kidney mitochondria.

In vivo treatments with propranolol inhibited state 3 respiration in rat liver mitochondria with glutamate, pyruvate+malate, beta-hydroxybutyrate and succinate as substrates. The extent of inhibition was generally higher for the acute treatment. In the kidney mitochondria, the extent of inhibition of state 3 respiration for glutamate, pyruvate+malate and ascorbate+TMPD was equal in both acute and chronic treatments. However, the contents of cytochromes in both liver and kidney mitochondria remained unaffected by either of the drug treatments. The results suggest that prolonged use of the drug can have toxic effects on the respiratory activity of mitochondria even in the peripheral tissues, in addition to the target tissues.

Altered kinetic attributes of Na(+)+K(+)-ATPase activity in kidney, brain and erythrocyte membranes in alloxan-diabetic rats.

Effects of alloxan-diabetes on kinetic attributes of Na(+)+K(+)-ATPase were examined in rat kidney, brain and erythrocyte membranes. The enzyme activity decreased significantly from 60-80% in the three membrane systems as a result of diabetic state. Kinetic analysis revealed that Km of the enzyme increased by 5- and 10-fold respectively in the kidney and brain membranes while registering a 50-60% decrease in Vmax. Ouabain binding studies revealed that in the kidney membranes the I50 value increased by 150-fold in diabetic animals with a significant decrease in number of ouabain molecules bound; at concentrations beyond 10(-7) M de-binding of ouabain occurred. For the brain membranes the I50 values for ouabain increased even more significantly (2000-fold increase) without any change in Hill coefficient for ouabain binding. Glycosylation studies revealed that its extent was highest for the brain and least for the kidney membranes which correlated to some extent with the I50 and Km values but not with Vmax. The results thus suggest that glycosylation in critical domains of the membrane and/or enzyme structure may play an important regulatory role. Physiological significance of these findings is discussed.

Effect of thyroidectomy and subsequent treatment with triiodothyronine on kidney mitochondrial oxidative phosphorylation in the rat.

The effect of thyroidectomy (Tx) and subsequent treatment with triiodothyronine (T3) on rat kidney mitochondrial oxidative phosphorylation was examined. Thyroidectomy resulted in lowering of state 3 respiration rates and cytochrome contents. Thyroidectomized animals administered with T3 (20 μg/100 g body wt) resulted in the nonsynchronous stimulation of state 3 respiration rates in kidney mitochondria with glutamate, β-hydroxybutyrate, succinate and ascorbate+TMPD as substrates. Cytochrome contents were also elevated differentially. Increase in the state 4 respiration rates was transient and reversible. However, primary dehydrogenases were not generally altered in the Tx and T3- treated Tx animals. The results thus indicate that the T3-treatment to Tx animals brings about differential and nonsynchronous increase in the respiratory parameters and respiratory chain components of kidney mitochondria.

Altered kinetic properties of liver mitochondrial membrane-bound enzyme activities following paracetamol hepatotoxicity in the rat.

The effects of treatment with subtoxic (375 mg/kg) and toxic (750 mg/kg) doses of paracetamol on NADH oxidase, succinoxidase and Mg2+-ATPase activities in rat liver submitochondrial particles were examined. In the NADH oxidase system, treatment with subtoxic doses of paracetamol resulted in a 37% increase in activation energy in the high temperature range (E1) while the phase transition temperature (Tt) for this system decreased by 9°C. Subtoxic doses caused a 43% decrease in E1. For the succinoxidase system, Tt decreased by 2·4 to 3·4°C after paracetamol administration. E2 increased by 42% only in the subtoxic-treatment group while E1 remained unaltered in both paracetamol-treated groups. For the Mg2+-ATPase system, subtoxic doses of paracetamol treatment did not change the values of E1, E2 and Tt whereas toxic dose treatment resulted in a 29% decrease in E2 with a concomitant increase in Tt by 2·4°C without any change in the value of E1 · The results thus suggest that treatment with toxic and subtoxic doses of paracetamol results in possible differential alterations in the membrane lipid milieu.

Altered kinetic properties of rat heart mitochondrial enzymes following experimental-thyrotoxicosis.

Effects of T3- and T4-induced thyrotoxicosis on temperature-dependent Arrhenius kinetics of succinate oxidase and Mg2+- and Mg2+ + 2,4-dinitrophenoldependent ATPase activities in rat heart mitochondria were examined, For succinate oxidase system, treatment with T3 and T4 caused increase in the energy of activation in high temperature range in a dose-dependent manner. For low temperature range, increase in energy of activation was apparent only with higher doses of the hormones; with low doses a small but reproducible decrease was evinced. The phase transition temperature decreased significantly under these conditions. For the Mg2+- and Mg2++2,4-dintrophenol- dependent-ATPase activities, the activation energy values in high temperature range decreased in general. Activation energy values in low temperature range recorded a generalized increase in the Mg2+-ATPase enzyme system while the value did not change significantly for the Mg2+ + 2,4-dinitrophenol-ATPase; phase transition temperature registered a small but reproducible decrease under these conditions. The results are suggestive of increased membrane fluidization possibly through increased proportion of unsaturated fatty acids. The differential effects seen for succinate oxidase and ATPase systems are consistent with different lipid protein domains of these enzyme systems.

Effect of experimentally induced thyrotoxicosis on oxidative energy metabolism in rat heart mitochondria.

Treatment of rats with T3 resulted in a significant decrease in body weight, while the heart weight increased. T4 treatment had less marked effect on body weights but resulted in decreased heart weights. Serum T4 levels decreased significantly with simultaneous increase of T3 level following T3 treatment, whereas with T4 treatment, levels of both T4 and T3 increased in the serum. Low doses of T3 (0·5 μg) caused decrease in mitochondrial protein content while high dose of T4 (1 μg), caused significant increase in mitochondrial mass. The state 3 respiration rates were significantly depressed following T3 and T4 treatments, in a substrate specific manner with the effects being more pronounced with T3; these responses with T4 were dose-dependent for succinate and ascorbate + N,N,N',N'-tetramethyl-p-phenylenedίamme. State 4 respiration rates also exhibited similar corresponding changes. ADP/O ratios were not changed but ADP-phosphorylation rates were decreased significantly particularly so with the T3-treated animals. Treatment with T3 also resulted in lowering of intramitochondrial cytochrome contents. Similar effects were seen also with higher doses of T4. The results thus indicate that T3- and T4- thyrotoxicosis results in impaired energy metabolism in heart mitochondria.