Biomedical subjects

G Liverini

Publications and source records attributed to G Liverini.

At least 37 records · Page 2Linked to original sources

PubMed1997

Energy balance and liver respiratory activity in rats fed on an energy-dense diet.

In the present study energy balance and liver respiratory activity were studied in rats fed on either a control diet or an energy-dense diet. Liver respiration was assessed both without added substrates and after the addition of hexanoate, glycerol, or sorbitol. The effect of ouabain on hexanoate-supported respiration was also determined. Metabolizable energy intake and energy expenditure increased in rats fed on an energy dense diet, but body-weight gain, as well as lipid and protein content, remained unchanged. When net energy expenditure, obtained excluding the total cost of storage, was expressed as a percentage of metabolizable energy, significant differences were found between the two groups of rats. This finding supports the presence of regulatory mechanisms in rats fed on an energy-dense diet, which are useful to counteract development of obesity. In addition, a significant increase in liver respiratory activity was found in rats fed on an energy-dense diet, both in the basal state and in that stimulated by added substrates. Na/K-pump-dependent O2 consumption also increased in rats fed on an energy-dense diet. The results indicate that a greater production of metabolic heat by the liver can contribute to the increased energy expenditure found in rats fed on an energy-dense diet.

Animal Feed↗

PubMed1997

Effect of a high-fat diet on energy balance and thermic effect of food in hypothyroid rats.

We have carried out measurements of energy balance in hypothyroid rats fed a low-fat or a high-fat diet for eighteen days. We have also measured cephalic and processing thermic effect of food (TEF) after a low-fat or a high-fat meal. Body lipid gain, carcass lipid content and gross efficiency were significantly (P < 0.05) higher in hypothyroid rats fed a high-fat diet compared with hypothyroid rats fed a low-fat diet, while metabolizable energy intake and energy expenditure remained unchanged. Cephalic TEF after a low-fat meal was significantly (P < 0.05) lower in hypothyroid rats fed a high-fat diet compared with hypothyroid rats fed a low-fat diet, while it was significantly (P < 0.05) higher after a high-fat meal than after a low-fat meal in hypothyroid rats fed a high-fat diet. No significant variation was found in processing TEF after a low-fat or a high-fat meal. Our results indicate that hypothyroid rats are unable to develop increased energy expenditure and increased TEF in response to a high-fat diet.

Animals↗

PubMed1996

Relationship between membrane potential and respiration rate in isolated liver mitochondria from rats fed an energy dense diet.

We studied the relationship between membrane potential and respiration rate in isolated liver mitochondria from rats fed an energy dense diet. We conceptually divided the system into blocks of reactions that produced or consumed mitochondrial membrane potential and then measured the kinetic response of these blocks of reactions to this potential using NAD-linked and FAD-linked substrates. We show that decreased respiration rate with an NAD-linked substrate is accounted for by decreased kinetic response of the substrate oxidation pathway to the potential. No variation in the kinetic response of the above blocks of reactions to the potential was found using an FAD-linked substrate. These results indicate that FAD-linked and NAD-linked pathways are differently affected in rats fed an energy dense diet.

Animal Nutritional Physiological Phenomena↗

PubMed1996

Hepatic fatty acid-supported respiration in rats fed an energy-dense diet.

The energy balance and hepatic fatty acid-supported respiration were studied in rats fed a control or an energy-dense diet. In addition, state 3 and 4 respiratory rates as well as ketone body production with palmitoylcarnitine as substrate were determined in isolated mitochondria. Metabolizable energy intake and energy expenditure increased in rats fed an energy-dense diet, but the gain in body weight and lipid content remained unchanged. No variation occurred in the mitochondrial palmitoylcarnitine utilization rate and ketone body production, but a significant increase in the mitochondrial content of ketone bodies and the serum levels was found in rats fed an energy-dense diet. Furthermore, we have shown a significant increase in fatty acid-stimulated respiration in hepatocytes from rats fed an energy-dense diet. The enhanced hepatic fatty acid utilization as an energy substrate found in rats fed an energy-dense diet may contribute to reduce the availability of lipids for storage, thus counteracting the development of obesity.

Animals↗

PubMed1996

Thermic effect of food in hypothyroid rats.

The regulatory and obligatory components of cephalic and gastrointestinal phases of the thermic effect of food (TEF) were measured in control and hypothyroid rats. A significant decrease (P < 0.05) in regulatory and obligatory components of cephalic and gastrointestinal TEF, after either a control or energy-dense meal, was found in hypothyroid rats compared with control rats. Our findings indicate that hypothyroidism is associated with a decreased thermogenic response to food which contributes to the reduced energy expenditure of hypothyroid rats. Our results also suggest that tri-iodothyronine is involved in the regulation of postprandial thermogenesis directly as well as through its influence on beta-adrenergic response and insulin release.

Animals↗

PubMed1995

Hepatic mitochondrial respiration and transport of reducing equivalents in rats fed an energy dense diet.

OBJECTIVE: To measure hepatic mitochondrial respiration as well as the ability of hepatic mitochondria to transport reducing equivalents by shuttle systems in rats fed an energy dense diet. DESIGN: Rats were fed a control (CD) or energy dense (ED) diet for 15 days. MEASUREMENTS: State 3 and State 4 oxygen consumption were measured in isolated mitochondria using glutamate+malate or pyruvate+malate as substrate. We also measured malate-aspartate shuttle activity and mitochondrial alpha-glycerophosphate dehydrogenase activity. RESULTS: ED rats, in comparison with CD rats, showed a significantly greater energy intake without a corresponding greater body weight gain and carcass lipid content. Compared to CD rats, ED rats also showed a significant increase in resting metabolic rate, which was abolished by propranolol. Hepatic mitochondrial state 3 respiration using glutamate+malate or pyruvate+malate as substrate as well as malate-aspartate shuttle activity significantly decreased, while mitochondrial alpha-glycerophosphate dehydrogenase significantly increased in ED rats compared to CD rats. CONCLUSIONS: Mitochondrial NADH oxidation is reduced and a greater fraction of cytoplasmic NADH can be transported to the mitochondria through the alpha-glycerophosphate shuttle and oxidized through the respiratory chain from complex II onwards. This mechanism could lead to a decrease in hepatic metabolic efficiency which is in line with the increased energy expenditure occurring in rats fed an energy dense diet.

Animals↗

PubMed1995

Sympathetically-mediated thermogenic response to food in rats.

The aim of this work was to assess the participation of the sympathetic nervous system in the thermogenic response to food in control and hyperphagic rats. Rats were fed either a control (CD) or energy dense (ED) diet. After 15 days, CD rats received a small (7 kJ) meal composed of either control or energy dense diet, while ED rats received a small meal composed of energy dense diet. The experiment was then repeated, with the exception that rats received a larger portion (35 kJ) of the test meal. The postprandial increase in oxygen consumption was measured for 30 min after the small meal and 90-180 min after the completion of the large meal. The measurements were made in saline-injected and propranolol-injected rats. ED rats exhibited hyperphagia as well as an increase of 32% in resting metabolic rate after a 16 h fast. The sympathetically-mediated postprandial increase in oxygen consumption was greater after an energy dense meal than after a control meal in CD rats, and was higher in ED rats than in CD rats fed an energy dense meal. It was concluded that the sympathetically-mediated increase in the thermogenic response to food, as well as the increase in fasting metabolic rate can help prevent obesity development in hyperphagic rats.

Animals↗

PubMed1994

Different effects of cold exposure and cold acclimation on rat liver mitochondrial fatty acid oxidation and ketone bodies production.

1. We have studied fatty acid oxidation and ketone bodies production in liver mitochondria from rats exposed to cold for 10 days and in rats adapted to cold for 40 days. We have examined State 3 respiration and ketone bodies production with palmitoylcarnitine as substrate in isolated mitochondria, together with mitochondrial protein mass and hepatocyte oxygen consumption. 2. Mitochondrial protein mass increases both in cold exposed and in cold adapted rats. 3. State 3 respiration and hepatocyte respiration increase only in cold exposed rats. 4. Ketone bodies production increases in cold adapted rats. 5. Taken together, our results suggest that the increased hepatic mitochondrial protein mass and the increased fatty acid oxidation subserve two different roles: an increase in ATP production in cold exposed rats and an increase in ketone bodies production in cold adapted rats.

Acclimatization↗

PubMed1992

Metabolic activity in isolated hepatocytes from cold exposed rats subjected to 24-hour fasting.

The aim of this work was to study the metabolic activity in isolated hepatocytes from control rats and rats exposed for 15 or 30 days to cold, all subjected to 24-h fasting. Hepatocyte oxygen consumption was used as an index of metabolic activity. The results show that 24-h fasting induces a decrease in energy expenditure at the level of the liver in cold-exposed rats but not in control animals.

Acclimatization↗

PubMed1992

Rat liver response elicited by long-term cold exposure.

We measured mitochondrial protein mass as well as State 4 and 3 respiratory rates using different substrates in isolated liver mitochondria from 30-day cold-exposed rats. In addition, we measured the respiration under different conditions of stimulation in isolated hepatocytes from long-term cold-exposed rats. The results show that long-term cold exposure elicits a significant increase in hepatic mass and mitochondrial protein mass. No variation was found in oxygen consumption of isolated mitochondria and hepatocytes. On the whole, the results indicate that long-term exposure elicits an increase in hepatic mitochondrial protein mass but not in hepatic oxygen consumption.

Adaptation, Physiological↗

PubMed1992

Relationship between resting metabolism and hepatic metabolism: effect of hypothyroidism and 24 hours fasting.

In this paper, we have examined the relationship between the changes in the resting metabolic rate (RMR) and the changes in hepatic metabolism induced by hypothyroidism and 24 h fasting. The results show that hypothyroidism induces a significant decrease in RMR, while 24 h fasting reduces RMR in euthyroid but not in hypothyroid rats. We have also measured oxygen consumption in isolated hepatocytes from euthyroid and hypothyroid rats, fed or fasted for 24 h. The results show that hypothyroidism is characterized by reduced hepatic oxygen consumption. On the other hand, 24 h fasting induces an increase in oxygen consumption in both euthyroid and hypothyroid rat liver cells, although the respiratory rates of hypothyroid rats were lower than those of euthyroid rats. The above findings, as a whole, show that hypothyroidism and 24 h fasting have similar effects on RMR but opposite effects on hepatic metabolism. In addition, a normal thyroid state does not appear to be necessary for the observed changes in hepatic metabolism due to 24 h fasting.

Animals↗

PubMed1992

Relationship between the resting metabolic rate and hepatic metabolism in rats: effect of hyperthyroidism and fasting for 24 hours.

We have examined the relationship between the changes in resting metabolic rate (RMR) and those in hepatic metabolism induced by hyperthyroidism and fasting for 24 h. We found that hyperthyroidism induced a significant increase in RMR, while fasting for 24 h reduced RMR in euthyroid but not in hyperthyroid rats. We have also measured oxygen consumption in isolated hepatocytes from euthyroid and hyperthyroid rats, fed or fasted for 24 h. Hyperthyroidism induced an increase in oxygen consumption in rat liver cells; fasting for 24 h increased respiratory rates in isolated liver cells from euthyroid but not from hyperthyroid rats. The findings showed that hyperthyroidism and fasting for 24 h have opposite effects on RMR but similar effects on hepatic metabolism. The results also indicated that the increase in RMR found in hyperthyroid rats is partly due to an increase in hepatic metabolism, while no correlation exists between variations in resting and hepatic metabolism induced by 24-h fasting.

Animals↗

PubMed1991

Hepatic selective adjustments in short-term cold exposed rats.

The metabolic adjustments which occur in rat liver cells during the first days of cold exposure have been investigated. We have measured both mitochondrial mass and oxidative capacities as well as ATP production after five and 10 days of cold exposure. In addition, we have measured plasma membrane Na+/K(+)-ATPase activity. Cold exposure elicited a significant increase in mitochondrial mass as well as in state 3 oxidative rates and ATP production in isolated mitochondria using various substrates. Moreover, our results show that Na(+)-pumping activity significantly increased after both five and 10 days of cold exposure. Our results suggest that during the first days of cold exposure liver cells undergo alterations which are useful for survival in the cold.

Animals↗

PubMed1991

The effect of thyroid state and cold exposure on rat liver oxidative phosphorylation.

In this paper we have examined the effect of cold exposure on hepatic mitochondrial state 3 respiration and ATP synthesis, using succinate as the substrate, in euthyroid, hypothyroid and hyperthyroid rats. The results show that cold exposure does not elicit any variation in the above parameters in euthyroid and hyperthyroid rats, whereas when hypothyroid rats are exposed to cold, a significant increase (about +45%) occurs in state 3 respiration and ATP synthesis. We have also measured succinic dehydrogenase specific activity and uncoupled respiration during cold exposure in various thyroid states. The finding that cold exposure elicits no variation in the above parameters indicates that there is some control on ATP synthase and/or adenine nucleotide translocator. The above findings, as a whole, suggest that cold exposure acts on oxidative phosphorylation only if triiodothyronine is lacking, by controlling ATP synthase and/or adenine nucleotide translocator.

Adenosine Triphosphate↗

PubMed1991

The effect of cold exposure on rat liver mitochondrial respiratory capacity.

1. The effect of cold exposure on the respiratory capacity of rat liver mitochondria has been studied using succinate as the substrate. 2. The mitochondria obtained in this study were well coupled, as shown by the RCR and ADP/O ratios. 3. In addition, durohydroquinone was used to eliminate the regulation of substrate supply. Likewise, we measured uncoupled respiration to evaluate the maximal electron flow through the respiratory chain. 4. We found that oxygen consumption using succinate or durohydroquinone + FCCP as substrates, as well as ATP production were not affected by cold exposure. 5. Our results also show that, when succinate is used, the maximal capacity of the respiratory chain is measured. 6. The data obtained do not support a role of the electron transport chain as a target of cold action.

Adenosine Diphosphate↗

PubMed1991

Effect of thyroid state and cold exposure on rat liver mitochondrial protein mass and function.

The effects of thyroid state on liver mitochondrial protein mass was investigated in rats at 24 and 4 degrees C, as was oxidative phosphorylation using substrates which represent the final catabolic products of the metabolic fuels. In rats at 24 degrees C, a significant increase in mitochondrial protein mass (about +40%) was observed only in hyperthyroid animals, while a significant increase due to cold exposure was found in hypothyroid (+45%) and euthyroid (+35%) rats. In rats at 24 degrees C, hypothyroidism significantly decreased the oxidation of glutamate and palmitoyl carnitine but not of pyruvate, while hyperthyroidism only increased the oxidation of palmitoyl carnitine. On the other hand, exposure to cold significantly increased the oxidation of glutamate and pyruvate only in the presence of tri-iodothyronine. Our results underline not only the fact that a simple and single hypothesis for thyroid effects cannot be adopted, but also that any study concerning oxidative metabolism should be carried out using different substrates and involving different pathways of oxidation.

Animals↗

PubMed1990

Elevated hepatic mitochondrial oxidative capacities in cold exposed rats.

1. Hepatic mitochondrial oxidative capacities were studied in rats exposed to cold for periods ranging from 5 to 15 days. The mitochondria obtained in this study were well coupled as shown by RCR and ADP/O ratios. 2. The liver mitochondria of cold exposed rats showed significantly increased respiratory rates (ng atoms of oxygen consumed min-1 mg prot-1), starting from day 10 of cold exposure, using lipid and non-lipid substrates. 3. For non-lipid substrates, the elevated respiratory rates found in the mitochondria could indicate an increased capacity to oxidize these substrates. For the lipid substrate, on the other hand, an enhanced oxidation through Krebs-cycle of a part of acetyl-CoA otherwise utilized to form ketone bodies, could also occur. 4. Taken together the results suggest that, during cold exposure, liver mitochondria could participate in cold adaptation mechanisms, by improving ATP production.

Acclimatization↗

PubMed1989

The effect of thyroid state on respiratory activities of three rat liver mitochondrial fractions.

In this paper we report that three different rat liver mitochondrial fractions, differing in density, exhibit differential effects when the animals are made hypo- or hyperthyroid. The investigations have been performed by correlating the protein content, the succinic dehydrogenase behaviour and the respiratory features of the three fractions in different thyroid states with morphometric-stereologic analysis the electron micrographic level. The results indicate that the thyroid hormone influences both the mass and the functionality of the heavy (H) and light (L) fraction. In hypothyroid rats the H fraction increases (+43%) while the L fraction decreases (-32%) and their respiratory activity is drastically reduced. Adenosine triphosphate (ATP) synthesis in the H fraction is also inhibited. Triiodothyronine (T3) administration to the above animals restores the values observed in control rats. At morphometric level we note in hypothyroid rats an increase in the number of mitochondria together with a concomitant increase in the average volume of a single mitochondrion. We are inclined to explain the above results through an action exerted by T3 on a hypothetical mitochondrial cycle starting with the formation of light organelles from heavy ones.

Animals↗