atractyloside and Hypothyroidism

Membrane permeability was examined in liver mitochondria isolated from hypothyroid rats. It was found that such a thyroid status provides substantial protection from membrane leakiness as induced by Ca2+ loading. Thus, these mitochondria are less prone to undergoing permeability transition than mitochondria from euthyroid rats. The above conclusion was reached on the basis of the following two facts: (1) hypothyroid mitochondria are not strictly dependent on the addition of ADP to retain high matrix Ca2+ concentrations, and (2) carboxyatractyloside, antimycin A or carbonyl cyanide-m-chlorophenyl hydrazone failed to promote Ca2+ efflux. We discuss the possible relevance of the low content of membrane cardiolipin as well as the low expression of the adenine nucleotide translocase as responsible for the resistance to membrane damage.

Topics: Adenosine Diphosphate; Animals; Atractyloside; Calcium; Cyclosporine; Hypothyroidism; Intracellular Membranes; Magnesium; Mitochondria, Liver; Permeability; Rats; Thyroidectomy

Maximal rates of O2 uptake by hepatocytes from hypothyroid, euthyroid, and hyperthyroid rats, in the absence of uncoupling agents or ionophores, were achieved by simultaneously stimulating ureogenesis and gluconeogenesis. Rates were increased by pretreatment of the donor animals with thyroid hormone. Only a minor part of the increase could be attributed to stimulation of the activity of plasma membrane (Na+ + K+)-ATPase. No synthesis of glycogen occurred, nor was there any evidence of pyruvate cycling under the conditions used, thus ruling out these processes as potential sources of ATP turnover. Calculation of the O2 uptake necessary to satisfy the energy requirements of gluconeogenesis and ureogenesis, based on anticipated ATP demand and an assumed P:O ratio of 3:1, invariably yielded a theoretical quantity that was less than the experimentally measured increase in O2 uptake. The difference between measured and calculated rates of respiration, possibly representing noncoupled respiration, was related to the thyroid status of the animal, being greatest in cells from hyperthyroid rats. In another experimental approach the O2 uptake associated with ATP synthesis was inhibited by the addition of oligomycin to hepatocytes incubated in the presence of substrates, thus abolishing ATP-coupled respiration. The magnitude of the ATP-coupled as well as the residual respiration was increased in response to thyroid hormone. Thyroid hormone increased the turnover of intramitochondrial ATP. These results imply that a considerable portion of the thermogenic effect of thyroid hormone may be mediated by a stimulatory action on metabolism not directly associated with extramitochondrial ATP-dependent synthetic processes.

Topics: Adenosine Triphosphate; Animals; Atractyloside; Energy Metabolism; Gluconeogenesis; Hyperthyroidism; Hypothyroidism; Liver; Male; Oxygen; Pyruvates; Pyruvic Acid; Rats; Rats, Inbred Strains; Thyroid Hormones

The respiratory capacities of hepatocytes, derived from hypothyroid, euthyroid and hyperthyroid rats, have been compared by measuring rates of oxygen uptake and by titrating components of the respiratory chain with specific inhibitors. Thyroid hormone increased the maximal rate of substrate-stimulated respiration and also increased the degree of ionophore-stimulated oxygen uptake. In titration experiments, similar concentrations of oligomycin or antimycin were required for maximal inhibition of respiration regardless of thyroid state, suggesting that the changes in respiratory capacity were not the result of variation in the amounts of ATP synthase or cytochrome b. However, less rotenone was required for maximal inhibition of respiration in the hypothyroid state than in cells from euthyroid or hyperthyroid rats, implying that hepatocytes from hypothyroid animals contain less NADH dehydrogenase. The concentration of carboxyatractyloside necessary for maximal inhibition of respiration was 100 microM in hepatocytes from hypothyroid rats, but 200 microM and 300 microM in hepatocytes from euthyroid and hyperthyroid rats, respectively, indicating a possible correlation between levels of thyroid hormone and the amount or activity of adenine nucleotide translocase. The increased capacity for coupled respiration in response to thyroid hormone is not associated with an increase in the components of the electron transport chain or ATP synthase, but correlates with an increased activity of adenine nucleotide translocase.

Topics: Animals; Antimycin A; Atractyloside; Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; Cells, Cultured; Hyperthyroidism; Hypothyroidism; Kinetics; Liver; Male; Oligomycins; Oxygen Consumption; Rats; Rats, Inbred Strains; Reference Values; Rotenone; Thyroid Gland; Triiodothyronine

Impaired phosphorylation efficiency in liver mitochondria from hypothyroid rats is paralleled by a defect in adenine nucleotide transport. Both of these lesions can be corrected within 15 min by a near-physiological dose of triiodo-L-thyronine. Measurement of the control strength of the translocator shows, however, that this step has a smaller share of the control for oxidative phosphorylation after thyroidectomy and that this is unaltered after 15 min by replacement therapy. Rapid control by triiodothyronine is thus exerted elsewhere than at this transfer and the effects of hormone on the translocator are likely to be indirect.

Topics: Animals; Atractyloside; Hypothyroidism; Kinetics; Male; Mitochondria, Liver; Mitochondrial ADP, ATP Translocases; Nucleotidyltransferases; Oxidative Phosphorylation; Rats; Thyroidectomy; Triiodothyronine