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G Liverini

Publications and source records attributed to G Liverini.

49 records · Page 3Linked to original sources
PubMed1989

Morphological and functional modifications of rat liver peroxisomal subpopulations during cold exposure.

A report is made (during cold exposure) of: a) the morphometric-stereologic analysis both on the whole rat liver peroxisomal population, and on 2 peroxisomal subpopulations having a diameter greater than 0.5 microns, and less than 0.5 microns, called Pe (Peroxisomes) and sPe (small Peroxisomes), respectively; b) the uricase and palmitoyl-coenzyme A oxidase activity assay on 2 classes of rat liver peroxisomes, sedimenting at 10,000 g and 27,000 g and containing Pe and sPe, respectively. The peroxisomal volume and number densities increase during cold exposure, reaching a maximum (+67% and +130%, respectively, P less than 0.05) at 10 days. These modifications are accompanied by an appreciable reduction of the average peroxisome volume (from 0.27 +/- 0.05 microns 3 to 0.19 +/- 0.02 microns 3) due to a major percentage increase of sPe during cold exposure. At a qualitative level, the formation of "clusters" and a stricter association between mitochondria and peroxisomes is also observed. Cold exposure increases the oxidative capacity of the whole peroxisomal compartment; in the Pe fraction the palmitoyl-CoA oxidase and uricase specific activity ratio is constant (about 0.1), during cold exposure, but in the sPe fraction this ratio increases significantly (from 0.05 to 0.09). The results indicate that the peroxisomal population is influenced during cold exposure, with the formation of a new peroxisomal population which is on average smaller and more specialized for the beta-oxidative activity. The possible involvement of peroxisomes in thermoregulatory thermogenesis during cold exposure is also discussed.

Animals↗
PubMed1989

Effects of 3,5,3'-triiodothyronine (T3) on rat liver peroxisomal compartment during cold exposure.

In this study, by enzymatic assays and morphometric-stereologic analyses, we show that the remodelling of the rat liver peroxisomal compartment, occurring during cold exposure, is largely influenced by the thyroid state of the animal. The research was performed both on the whole rat liver peroxisomal population and on 2 peroxisomal subpopulations: one having a diameter greater than 0.5 microns, sedimenting at 10,000 g and called Pe (Peroxisomes); and the other having a diameter less than 0.5 microns, sedimenting at 27,000 g and called sPe (small Peroxisomes). The increase in the peroxisome number and in the peroxisome volume densities, elicited by cold exposure, is greatly reduced in hypothyroid cold-exposed animals (-63% and -40% respectively, P less than 0.01), while triiodothyronine (T3) administration to these rats restores the values observed in normal cold-exposed animals. The "clusters" and the strict association between mitochondria and peroxisomes, more frequently found in cold-exposed rats, are rarely observed in hypothyroid cold-exposed animals. At peroxisomal enzymic level, the thyroid hormone inhibits, during cold exposure, the uricase activity (-29% in Pe and -40% in sPe), and stimulates the palmitoyl-coenzyme A oxidase activity (+44% in Pe and +88% in sPe). The results also demonstrate that T3 exerts all these effects by acting principally on sPe.

Animals↗
PubMed1988

Light mitochondria and cellular thermogenesis.

We show that remarkable differences exist among 3 mitochondrial subpopulations with regard to oxidation-phosphorylation coupling. In the heavy fraction (sedimenting at 3,000 g) ATP synthesis is optimized while in the medium and light fractions (sedimenting at 10,000 and 27,000 g, respectively) heat production tends to be optimized as the mitochondrial size decreases. As the oxygen consumption of the L-fraction drastically increases (+150%) after fifteen days of cold exposure, such differences have remarkable implications for the mechanism of cellular thermogenesis and its regulation.

Adenosine Triphosphate↗
PubMed1988

Mitochondrial DNA, RNA and protein synthesis in normal, hypothyroid and mildly hyperthyroid rat liver during cold exposure.

We have examined in isolated liver mitochondria the effect of cold exposure on DNA, RNA and protein synthesis in normal, hypothyroid and mildly hyperthyroid rats. In normal rats DNA polymerase activity increased from the first day of cold exposure remaining high up to the fifteenth day. RNA polymerase and protein synthesis were stimulated from the fifth day of cold exposure, maintaining a high level up to the fifteenth day. These activities were related to serum triiodothyronine (T3) levels. Indeed propylthiouracil (PTU) administration to cold-exposed rats drastically depressed the above activities, whereas T3 administration to PTU-treated cold-exposed rats restored them to about the values prevalent in normal cold-exposed rats. The translation products analyzed by gel electrophoresis showed that different effects may be exerted by T3 depending on whether its circulating levels are physiologically or pharmacologically modified. These findings suggest that T3 may be involved in the regulation of the acclimation process by acting, presumably with a permissive role, on those activities which determine a modification of the mitochondrial morphometric features and an increase in mitochondria number and turnover.

Animals↗
PubMed1986

Tri-iodothyronine enhances the formation of light mitochondria during cold exposure.

The effect of cold exposure and of PTU and PTU + T3 administration on the protein content and succinic dehydrogenase activity of three mitochondrial populations obtained from rat liver was examined. Our results indicated the following: Succinic dehydrogenase activity increases mainly in the light mitochondrial fraction of cold-exposed rats. PTU administration of cold-exposed animals does not affect the increment in enzyme activity of the heavy fraction but blocks the increment of the light fraction. PTU + T3 administration restores succinic dehydrogenase activity to the values prevalent in normal cold-exposed rats. These findings suggest that thyroid hormone may stimulate the formation of light mitochondria during cold exposure.

Acclimatization↗
PubMed1985

Alteration in hepatic mitochondrial compartment of cold-acclimated rats. Association with enhanced triiodothyronine serum levels. A morphometric/stereologic study by electron microscopy.

In cold-exposed rats, the circulating levels of free and total T3 rapidly increase and reach higher values after 2 h, 70% and 80%, respectively. These values remain constant during cold exposure and return to normal values after few hours of re-exposure to room temperature. A remarkable modification of the mitochondrial compartment in rat hepatic cells is associated with these hormonal variations. The morphometric stereologic analysis shows that after 10 days of cold exposure the number of mitochondria per nucleus is nearly doubled (from 1,912 to 3,414), the total volume of the mitochondrial compartment per nucleus increases by about 40% (from 21% to 29%), and the mitochondrial membrane surfaces per nucleus increase too (from 7,233 square microns to 11,597 square microns for the outer membranes; from 31,572 square microns to 42,603 square microns for the inner membranes + cristae). The mean mitochondrial volume decreases by about 25%. This probably indicates, the formation of new organelles by division of pre-existing mitochondria. On re-exposure to room temperature, there is a return to normal values. The present data suggest the existence of a physiological long-term mechanism for the regulation of cellular thermogenesis during cold exposure (increase in number of mitochondria per cell), associated with enhanced levels of T3.

Acclimatization↗
PubMed1983

Thyroid state and mitochondrial population during cold exposure.

Young rats exposed to the cold (4 degrees C) for 15-25 days exhibit remarkable modifications in their thyroid state and in the mitochondrial population of target organs such as liver. The serum total and free T3 levels more or less doubled (from 77 +/- 7 to 130 +/- 7 ng/100 ml and from 350 +/- 25 to 530 +/- 25 pg/100 ml, respectively) after 2 h of exposure while the serum total T4 levels underwent a limited and transitory increase; mitochondrial alpha-glycerophosphate dehydrogenase activity increased. On re-exposure to room temperature the thyroid state returned to normal. Cold exposure diminished the cellular volumes of hepatic cells, while the successive warm re-exposure increased the number of liver cells. The number of mitochondria per nucleus increased after 5 days of cold exposure and doubled after 10 days (from 1,200 +/- 120 to 2,400 +/- 130), while the mean protein content per organelles exhibited an exactly contrary trend. These results suggest that during cold acclimatization, the thyroid, the thyroid plays a role in inducing an augmentation of mitochondrial membrane surfaces per cell by stimulation of the mitochondrial protein synthesizing mechanism. At present, it is not possible to establish whether these effects are due to transcriptional modifications of the nuclear genome only or, more likely, to a dual action at nuclear and mitochondrial level.

Animals↗
PubMed1981

In vitro binding of triiodothyronine to rat liver mitochondria.

Saturable high affinity T3 binding sites were detected in a mitochondrial fraction enriched in internal membranes and partly solubilized by Triton X-100. Specific T3 binding to the solubilized sites, only detected at low T3 concentrations, was optimal at pH 8.0 and not dependent upon the presence of divalent cations or reducing agents; it was destroyed by heat and proteolytic enzymes. The solubilized T3 binding sites were distributed, after Sephadex G-200 gel filtration, between two peaks of similar affinity for T3 (Ka congruent to 5 x 10(10)l/mol) and similar binding characteristics. T3 was bound with a high stereospecificity, while some analogues of biological importance (L-T4; 3,5,3'-triiodothyroacetic acid; 3,3';-diiodo-L-thyronine) competed with L-T3 in the same range of low concentrations. This suggests that the high affinity mitochondrial T3 binding sites could be of biological relevance in the mitochondrial metabolism.

Animals↗
PubMedDate not supplied

Thyroid state and mitochondrial population during maturation and ageing.

The authors have determined the serum thyroid hormone levels [total and free triiodothyronine (T3), thyroxine (T4)], the liver T3 content, the mitochondrial alpha-glycerophosphate dehydrogenase activity (alpha-GPDH) and the number of mitochondria per cell in the rat from birth to old age. The serum levels of both thyroid hormones are modified with maturation and ageing in an essentially similar way: they increase from low values at birth to remarkably high values around 12 days, and then remain constant. The T3 liver content firstly increases (from birth to 14 days of life) and then maintains constant values. During the first two postnatal weeks, therefore, free serum T3 and liver T3 display a similar behavior. The alpha-GPDH activity of liver mitochondria was found constant from birth to old age. This might suggest either that the control of the alpha-GPDH activity is, at birth, under complex hormonal control, or that the nuclear receptors associated with the alpha-GPDH genes are precociously synthesized. The number of mitochondria per cell, at birth, is half the adult values, strongly increasing in number at weaning and remaining constant afterwards. The effect of thyroid hormones on the mitochondrial population during maturation, when low levels of serum T3 and T4 occur naturally, appears to be quite different from that induced experimentally by thyroidectomy.

Aging↗
PubMedDate not supplied

Effect of thyroidectomy and in vivo administration of triiodothyronine on DNA synthesis in isolated mitochondria.

The experimental conditions were studied which allow hormonal levels to affect the incorporation of labelled deoxyribonucleosides triphosphates (dNTP's) into mitochondrial DNA by isolated liver mitochondria, obtained either from thyroidectomized young male rats (T) or from animals of the same age thyroidectomized and then treated with triiodothyronine (T + T3). It was demonstrated that: (a) extramitochondrial DNA, on which extramitochondrial DNA polymerase may act, was absent; (b) the permeability to dNTP's, the thymidine kinase activity, the energy supply, and the nuclease activities were unaffected by hormonal conditions; (c) the bacterial contaminations contribute for only 1% to incorporation. The characterization of incorporation product showed that: (a) such product was indeed DNA, as it was DNase-degradable for about 90%; (b) the labelled DNA was indeed mitochondrial DNA, as a 10 minutes preincubation with acriflavine or ethydium bromide (Eth. Br.) inhibited the synthesis by 90%.

Animals↗
PubMedDate not supplied

DNA synthesis in isolated mitochondria: effect of thyroidectomy and of triiodothyronine administration in vivo.

The incorporation was studied of labelled deoxy-ribonucleosides triphosphates into acid-insoluble material by isolated liver mitochondria, obtained from either normal young male rats, or thyroidectomized at weaning, or thyroidectomized and then treated with triiodothyronine (T3). The incorporation extents in normal animals decreased with the age starting from the weaning until the 210th day. Thyroidectomy reduced the incorporation extent to about 70% of the values observed in normal animals. During the T3 treatment of thyroidectomized rats a sharp increase of incorporation was observed one day after the first administration, followed by a decrease from the 1st to the 3rd day; successively the incorporation extent remained unchanged until the 12th day. Finally, evidence was provided that T3 doses used were thyreomimetic and definitely lower than the thyreotoxic ones.

Aging↗