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O Michel

Publications and source records attributed to O Michel.

At least 163 records · Page 9Linked to original sources
PubMed1983

Effects of short- and long-term thyroidectomy on mitochondrial and nuclear activity in adult rat brain.

We compared subcellular activities in brain and liver at various times after thyroidectomy. Male S.D. rats were used on days 5, 10 or 60 after surgery. Mitochondrial properties were estimated by determining the respective activities of oxidative phosphorylation, succinate oxidase, succinate and beta-hydroxybutyrate cytochrome c reductase and alpha-glycerophosphate dehydrogenase. Nuclear activity was estimated by measuring the RNA polymerase I activity. In brain, RNA polymerase I activity already declined at 5 days after thyroidectomy, whereas mitochondrial respiratory enzymes decreased significantly only after 60 days. In liver, nuclear RNA polymerase I and mitochondrial enzyme activities were observed to drop simultaneously by the 5th day after thyroid removal. On the other hand, daily T3 s.c. injections, 0.25 microgram/100 g B.W., were given for 10 days to rats immediately after thyroidectomy (10 days Tx) or to chronically hypothyroid rats (60 days Hth). Hormonal treatment either maintained or restored subcellular activities to their normal level, both in brain and liver. These data suggest that the metabolic properties of brain mitochondria are sensitive to thyroid hormones, but that the brain needs less iodothyronines than other organs. The fast reduction of RNA polymerase I by thyroidectomy and its subsequent restoration by T3 suggest that the nuclear activity greatly depends on thyroid status.

Animals↗
PubMed1982

[Metabolic effects of 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT) in constant infusion by osmotic minipump to hypothyroid rat (author's transl)].

Our experiments show that the T3 nonhalogenated analog 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT) exhibits the general activities of thyroid hormones. DIMIT delivered to hypothyroid Rat by constant infusion or sc injections increases bodyweight gain, BMR before or after epinephrine and phosphorylative oxidation of liver mitochondria.

Animals↗
PubMed1982

Effect of thyroidectomy on pregnenolone and progesterone biosynthesis in rat adrenal cortex.

The effects of thyroidectomy on pregnenolone and progesterone biosynthesis were investigated in rat adrenal cortex mitochondria and microsomes. The sequential hydroxylations of cholesterol, and the latter's side-chain cleavage, which constitute the limiting step in steroidogenesis, were studied by measuring oxygen consumption rates in the presence of cholesterol derivatives. The addition of (20R)-hydroxycholesterol, (22R)-hydroxycholesterol or (20R,22R)-dihydroxycholesterol stimulated these rates, but addition of cholesterol or (22S)-hydroxycholesterol had little effect. Thyroidectomy significantly reduced oxygen consumption rates in the presence of the sterols by about 30%. Oxygen uptake was small in the presence of respiratory inhibitors; the addition of sterols raised this uptake but subsequent thyroidectomy did not change it. Rat adrenal cortex mitochondria and microsomes converted pregnenolone ino progesterone through 3 beta ol dehydrogenase/delta 4-5 isomerase, in two different successive steps. Values for enzyme activities were 0.18, 0.26 and 0.81 nmol progesterone/min/mg protein for the overall complex, the 3 beta ol dehydrogenase and the delta 4-5 isomerase respectively. All enzyme activities were unchanged by thyroidectomy. Similar results were obtained for corresponding microsomal activities whose values were in the same range. For both microsomes and mitochondria, the dehydrogenase reaction was the limiting step in the enzyme reaction leading to progesterone formation from pregnenolone. The limiting step in corticosteroidogenesis leading to prenenolone formation by an NADPH-dependent step was slowed down by thyroidectomy, probably because the reaction that transfers energy from NADH to NADP was inhibited. The enzyme complex leading to progesterone which involves NAD+ as cofactor, was unchanged by thyroidectomy. Thyroid hormones may therefore affect the availability of the energy mechanisms connected with the proton motive force, since thyroidectomy reduces both the phosphorylative oxidation and energy-dependent hydroxylation reactions involved in steroidogenesis.

Adrenal Cortex↗
PubMed1982

Effect of thyroidectomy on the rat adrenal cortex enzyme activities involved in corticosterone and aldosterone biosynthesis.

The effect of thyroidectomy on corticosterone and aldosterone biosynthesis, in rat adrenal cortex, were investigated in vitro. Thyroidectomy slowed down by about 30% the activity of microsomal 21 hydroxylase and mitochondrial 11 beta hydroxylase, the two stages leading to corticosterone formation from progesterone. The plasma corticosterone concentration also diminished in thyroidectomized rat. The mitochondrial enzyme system catalyzing the conversion of corticosterone into aldosterone included both 18 hydroxylase and 180H dehydrogenase. In the absence of thyroid hormone, values of both enzyme activity slowed down by about 30%. Thus thyroidectomy induced a general decrease in all mitochondrial hydroxylation processes requiring NNADPH as energetic cofactor. Mitochondrial NADPH was mainly synthesized by the activity of NADP+ malic enzyme and pyridine nucleotide transhydrogenase; the activity of both enzymes was determined in submitochondrial particles from adrenal cortex of normal and thyroidectomized rats. The activity of NADP+ malic enzyme and non energy-dependent transhydrogenase in the direction of NADPH formation dropped significantly after thyroidectomy, thus reducing the amount of NADPH available for hydroxylating mechanisms. The results should be compared to the large rise in th cytosolic malic enzyme level caused by thyroidectomy. The latter also ensured that the transhydrogenase reaction did not vary in the direction of NADP+ formation. Further, the drop in NADPH synthesis after thyroidectomy was coupled with a decrease in phosphorylation rate of added ADPH by adrenal cortex mitochondria of thyroidectomized rat. These findings might account for the general decline in the energy-dependent processes involved in steroidogenesis, a decline mainly due to the lowering of the H+ ions gradient driving ATP and NADPH synthesis through electron transfer.

Adrenal Cortex↗
PubMed1978

[Effect of thryoidectomy on the properties of rat liver mitochondria during liver regeneration].

The properties of regenerating rat liver mitochondria are not changed by the thyroidectomy. Thus, hepatectomy induces, in thyroidectomized rats as in normal ones, a decrease in the activity of the outer membrane enzymes, a stimulation of oxidative phosphorylations and an increase of the turn over rate of mitochondrial proteins. Thyroid hormones do not seem to have a major effect upon the liver regeneration mechanism.

Animals↗
PubMed1975

[Effects of thyroidectomy of the rat on the structure and functions of skeletal muscle mitochondria].

Mitochondria used in the present study were isolated from skeletal muscle of normal and thyroidectomized rats. The preparations were controlled by electron microscopy. It was not possible to find any morphological change induced by thyroidectomy, nevertheless, some difference appeared in the cytochrome contents which were slightly decreased. Oxygen consumption rates of thyroidectomized rat mitochondria were decreased when the particles were maintained in states 3 and 4 in the presence of various substrates, but the P/O ratios were not modified. The activities of mitochondrial enzymes were in general slightly affected by thyroidectomy except for glycerol-1-phosphate cytochrome c reductase and NADH rotenone sensitive cytochrome c reductase which were decreased and for glutamate dehydrogenase activity which was increased. The tRNA nucleotidyltransferase activity found in the mitochondrial matrix was not influenced by the absence of thyroid secretion. Normal rat muscle mitochondria incorporate 14C-leucine with an artificial ATP-generating system or with a respiratory substrate. The amino acid incorporation was decreased by thyroidectomy. Muscle mitochondria analyzed by polyacrylamide gel electrophoresis contained more than 30 protein components with MW ranging from 10.000 to 135.000. Thyroidectomy lowered the amount of a fraction of about 54.000 MW. It is not impossible that all the data observed in the absence of thyroid secretion are in relation with changes induced in the mitochondrial genome as previously shown in mitochondria isolated from liver or thyroidectomized rats.

Animals↗