Biomedical subjects

A Lanni

Publications and source records attributed to A Lanni.

42 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↗