Surendra S. Katyare

Effect of thyroid deficiency on oxidative phosphorylation in rat liver, kidney, and brain mitochondria.

Abstract The effect of thyroidectomy on oxidative metabolism of rat liver, kidney, and brain mitochondria has been examined. The respiration in liver, kidney, and brain mitochondria was affected differentially after thyroidectomy, the common effect in all the tissues being the impairment in state 3 as well as state 4 rates of succinate oxidation. Thyroidectomy did not have any effect on ADP O ratios; however, compared to normal, respiratory control indexes were, in general, somewhat higher. Thyroidectomy also did not alter total ATPase activity of liver, kidney, and brain mitochondria, although the basal ATPase activity had decreased significantly under these conditions. The cytochrome content of the mitochondria also showed tissue-specific changes after thyroidectomy; however, no significant changes in the absorption characteristics of the cytochromes were seen. The succinate and glutamate dehydrogenase activities of mitochondria from liver, kidney, and brain were not affected by thyroidectomy, thereby ruling out the possibility that the decrease in substrate oxidation may be due to alterations in the primary dehydrogenase levels. It is concluded that thyroid hormone(s) may have a tissue-specific role in regulating the metabolic functions of mitochondria.

Effect of experimental thyrotoxicosis on oxidative phosphorylation in rat liver, kidney and brain mitochondria

Coupled phosphorylation was examined in liver, kidney and brain mitochondria from rats made thyrotoxic by injecting repeated doses of triiodothyronine. Liver and kidney mitochondria were maximally affected under these conditions, whereas effects on brain mitochondria were marginal. State-3 respiration rates with succinate decreased considerably in all the tissues, whereas glutamate oxidation increased in liver, but decreased in kidney and brain mitochondria. Oxidation rates of beta-hydroxybutyrate decreased in kidney and brain mitochondria but were not significantly affected in liver mitochondria. Oxidation of ascorbate + TMPD was not affected. State-4 respiration rates increased in general with all the substrates resulting in lowering of the RCI. The ADP/O ratios decreased in a site-specific manner in the mitochondria from the three tissues. The content of cytochrome b decreased in all three tissues, whereas the content of cytochrome c + c1 increased in liver and kidney but decreased in brain. The content of cytochrome a, however, was not significantly affected. Basal and Mg2+-stimulated ATPase activities increased in mitochondria of liver and kidney but not in those of brain; total ATPase activities, however, were not altered. The results imply that excessive levels of thyroid hormones over normal in the serum can lead to impairment of mitochondrial energy metabolism in a tissue-specific manner.

Impaired mitochondrial oxidative energy metabolism following paracetamol-induced hepatotoxicity in the rat.

1 Effects of paracetamol treatment in vivo at subtoxic (375 mg kg−1 body weight) and toxic (750 mg kg−1 body weight) doses on energy metabolism in rat liver mitochondria were examined. 2 Paracetamol treatment resulted in a significant loss in body weights without affecting the liver protein contents. Toxic doses, however, resulted in 21% decrease in the yield of mitochondrial proteins. 3 Subtoxic doses of paracetamol did not, in general, affect the respiratory parameters in the liver mitochondria except in the case of succinate where both the state 3 respiration and the ADP‐phosphorylation rates increased by 28%. 4 Toxic doses of paracetamol caused 25 to 47% decrease in the state 3 respiration rates depending on the substrate used. ADP/O ratios also decreased significantly with pyruvate + malate and succinate as the substrates. Consequently, ADP‐phosphorylation was impaired significantly from 20 to 63%. 5 Subtoxic doses of paracetamol resulted in increased contents of cytochrome c + c1 while the toxic doses caused lowering of the cytochromes aa3 and b contents. 6 Glutamate and succinate dehydrogenase activities decreased in both the experimental groups while Mg2+‐ATPase activity was impaired only after toxic dose‐treatment. 7 The results show that toxic doses of paracetamol result in impaired energy coupling in the liver mitochondria. Effects of subtoxic doses were also demonstrable in terms of impaired dehydrogenases activities.

Effect of 2, 4-dinitrophenol (DNP) on oxidative phosphorylation in rat liver mitochondria.

The effects of a range of DNP concentrations on ADP/O ratio, respiratory control index (RCI), and stimulation of latent ATPase activity of mitochondria have been studied using various substrates. The first and third sites of phosphorylation were found to be more sensitive to DNP action as compared to the second site. No correlation could be seen between any of the three parameters studied. Fluoride was inhibitory to the stimulation of ATPase by DNP only in presence of high concentrations of DNP, but had no inhibitory effect at low DNP concentrations. The inhibitory effects of fluoride and substrates were not additive.

Enhanced oxidative phosphorylation in rat liver mitochondria following prolonged in vivo treatment with imipramine

1 Effects of prolonged in vivo administration of the tricyclic antidepressant drug imipramine on oxidative energy metabolism in rat liver mitochondria were examined. 2 Imipramine treatment resulted in an increase in state 3 respiration rates with all the substrates tested as early as one week after treatment; this was sustained through the second week of treatment. 3 The changes in respiration rates were accompanied by a selective increase in the intramitochondrial cytochrome aa3 and c + c1 contents after both one and two weeks of treatment. 4 Administration of imipramine did not alter the total liver protein content per g tissue, the mitochondrial protein content per g tissue or the mitochondrial yield. 5 Kinetic analyses of succinoxidase activity in terms of Arrhenius plots indicated possible alterations in mitochondrial membrane lipid milieu and membrane fluidity after the drug treatment, especially in the second week.

Altered energy coupling in rat heart mitochondria following in vivo treatment with propranolol

Effects of acute and chronic treatment with propranolol on oxidative phosphorylation in rat heart mitochondria were examined. Acute propranolol treatment resulted in inhibition of coupled respiration with pyruvate + malate and succinate as substrates. Chronic treatment resulted in decreased state 3 respiration rates with all the substrates employed. The net effect of propranolol treatment was decreased ATP-phosphorylation rates suggesting that this was possibly one of the modes of its cardiodepressant activity. Additionally, chronic propranolol treatment brought about a decrease in the content of cytochrome c + c1 in heart mitochondria. Estimation of propranolol concentrations in serum, whole tissue homogenate and heart mitochondria indicated that although the mitochondria accumulated the highest amount of the drug, the intramitochondrial concentration of the drug was one or two orders of magnitude lower than that which is required to bring about inhibition of respiration under in vitro conditions. Besides, the concentrations reached under acute and chronic treatment conditions were almost comparable. The results, therefore, suggest that the action of the drug in vivo may involve more intricate mechanisms than those observed under in vitro conditions.

REGULATION OF MITOCHONDRIAL MEMBRANE PROTEIN TURNOVER BY THYROID HORMONE(S)

Effects of thyroidectomy on turnover rate of proteins of rat liver mitochondria, mitochondrial membranes and microsomes were examined. Thyroidectomy resulted in a significant increase in the half-lives of whole mitochondria and inner membrane-matrix, the effect being less pronounced on the half-lives of outer mitochondrial membrane and microsomes.

Altered cerebral protein turnover in rats following prolonged in vivo treatment with nicotine.

Abstract: Turnover rates of cerebral proteins were examined in control adult rats and in those subjected to prolonged in vivo treatment with “low” (0.02 mg/ml) or “high” (0.04 mg/ml) doses of nicotine (added to drinking water), using [14C]bicarbonate as the label. It was found that the turnover of proteins in various subcellular fractions consisted of two distinct components turning over at a “fast” or a “slow” rate and having relatively short or long half‐lives, respectively. Thus in control animals the half‐lives of the protein components turning over at a fast rate ranged from 1.31 to 3.61 days whereas for those turning over at a slow rate the half‐lives ranged from 8.56 to 24.28 days. Treatment with low doses of nicotine resulted in a more rapid turnover of nuclear fast turning over component with a concomitant decreased turnover of homogenate, cytosol, mitochondrial, and microsomal proteins; in the synaptosomal membranes this component disappeared altogether. The half‐lives of the slow turning over components decreased in general from 14.3 to 33.3% with the exception of the nuclear proteins, where the half‐life increased by 71.1%. Turnover of microsomal proteins was not affected. When the animals were given a high dose of nicotine, the turnover of fast components became even more rapid for nuclear, myelin, and microsomal proteins with a decrease in half‐life from 26.6 to 32.3%. By contrast, half‐lives of synaptosomal and mitochondrial proteins increased by 16.1–89.3%. These changes were not reflected in the turnover rate of whole homogenate proteins. Turnover rates of even the slow components increased for cytosol, nuclear, homogenate, and myelin proteins with decrease in t1/2 from 22.9 to 60.2%. By contrast, t1/2 of microsomal and mitochondrial proteins increased by 51.1 and 66.4%. Turnover of synaptosomal proteins was not affected under these conditions. Treatment with nicotine also brought about a small but reproducible increase in the rate of turnover of liver homogenate proteins which is attributable almost completely to the nuclear proteins. With low doses of nicotine half‐life of mitochondrial proteins increased by 7.2% whereas that of microsomal proteins decreased by 8.5%. The results thus emphasize that in vivo effects of nicotine are more specific for cerebral protein metabolism.

Effect of 3,5,3′-tri-iodothyronine on cellular growth and oxygen consumption in neonatal rat brain

The effect of thyroid deficiency and treatment with tri-iodothyronine (T3) on oxygen consumption by neonatal (6-day-old and 15-day-old) rat brain was examined using glutamate, β-hydroxybutyrate, succinate and ascorbate+TMPD as substrates. The respiration rates decreased significantly in 15-day-old hypothyroid pups. Treatment of normal and of hypothyroid pups with T3 resulted in a significant increase in the respiration rate at both ages. Respiration rates with glucose as the substrate were not affected under these conditions.

Effect of tri-iodothyronine treatment on electrophoretic mobilities of rat liver mitochondrial fractions

Abstract Heterogeneity of mitochondrial fractions, observed earlier in respect of membrane-bound enzyme profiles and protein turnover, is not reflected in their electrophoretic mobilities. Administration of tri-iodothyronine to thyroidectomised rats results in decreased electrophoretic mobilities of all the mitochondrial fractions.