Mitochondrial respiration and triiodothyronine concentration in liver from postpubertal and adult rats.

The purpose of this study was to investigate the decline in rat liver mitochondria respiration found in adult rats compared to younger ones, and to find a link between this respiratory impairment and a tissue hypothyroidism state. To this end, hepatic concentration and serum levels of triiodothyronine were measured in postpubertal rats (60 days old) and adult rats (180 days old). In addition, in these rats we measured oxidative phosphorylation in homogenate together with coupled and uncoupled respiration in isolated mitochondria using succinate or durohydroquinone as substrate. We found that mitochondria from adult rats consumed less oxygen compared to younger rats due to lower electron transport chain and phosphorylating system activity. In addition, we found that in state 4 condition, mitochondria from adult rats consumed less oxygen than mitochondria from young rats. Finally, we found a decrease in liver triiodothyronine concentration in adult rats. In conclusion, the results of this study show that hepatic mitochondria in adult rats have a decreased ATP synthesis capacity and proton permeability, both consistent with the tissue hypothyroidism found in the liver of adult rats.     

The effects of magnesium on state 3 respiration of liver mitochondria from control and cold-acclimated rats and hamsters.

1. Increasing the Mg2+ concentration results in a depression of succinoxidase-linked state 3 respiration of liver mitochondria from both control and cold-acclimated rats and hamsters. 2. It appears that in the cold-acclimated hamster, liver mitochondrial respiration is more sensitive to changes in Mg2+ levels than that of the rat.     

Mitochondrial respiration in heart, liver, and kidney of copper-deficient rats

Morphological observations in some tissues indicate that dietary copper deficiency results in structural damage to mitochondria. The purpose of this study was to determine whether mitochondrial function is impaired as well. Male, weanling Sprague-Dawley rats were fed diets deficient or sufficient in copper for 4 weeks. Mitochondria were isolated from heart, liver, kidney cortex, and kidney medulla. P/O ratio, state 3 and state 4 respiration rates (oxygen consumed in the presence and absence of ADP, respectively), and acceptor control index (ratio of state 3:state 4) were determined using succinate or pyruvate/malate as substrate. State 3 respiration rate in mitochondria from copper-deficient hearts and livers was lower than in mitochondria from copper-sufficient hearts. Copper deficiency reduced the state 4 respiration rate only in cardiac mitochondria. Neither respiration rate was affected by copper deficiency in mitochondria from kidney medulla or cortex. P/O ratio was not significantly affected by copper deficiency in any tissue examined. Acceptor control index was reduced only in liver mitochondria. The observed decreases in respiration rates are consistent with decreased cytochrome c oxidase activity, shown by others to occur in mitochondria isolated from hearts and livers of copper-deficient rats.     

Increased respiration in skeletal muscle mitochondria from cold-acclimated ducklings: uncoupling effects of free fatty acids

Intermyofibrillar mitochondria from skeletal muscle (m. gastrocnemius) and liver mitochondria were isolated from cold-acclimated (4 degrees C) or control (30 degrees C) 4-week old ducklings. The respiratory rate of isolated mitochondria, with Na-succinate as substrate, was followed polarographically at 25 degrees C in order to determine the basal respiratory rate, the rate of respiration in the presence of free fatty acids (FFA) (Na-palmitate), and the fully uncoupled rate, after addition of FCCP. The basal respiration (which in liver mitochondria was unaffected by acclimation to cold) was higher (+53%) in intermyofibrillar mitochondria from cold-acclimated ducklings than from controls, and the maximal FCCP-stimulated respiration was also increased (+98%) by acclimation to cold. FFA-stimulated respiration increased as a function of FFA concentration in both types of mitochondria. The increase in respiration due to FFA was about double in intermyofibrillar mitochondria from cold-acclimated ducklings than that of controls, but in liver mitochondria there was no increase due to cold. The membrane potential was estimated by the dye safranine in the absence or in the presence of FFA in the incubation medium. There were no significant differences in the basal membrane potential in the two groups and the addition of FFA led to the same depolarization in both groups. The significance of these alterations for acclimation to cold is discussed.     

Mitochondrial alterations and apoptosis in smooth muscle from aged rats

We studied changes in mitochondrial morphology and function in the smooth muscle of rat colon. Under confocal microscopy, tissues loaded with potentiometric dye displayed rapid and spontaneous depolarization. Cyclosporin A (CsA), inhibitor of the permeability transition pore (PTP), caused an increase in mitochondrial membrane potential (DeltaPsim) in tissues from adult young animals. In aged rats these changes were not observed. This suggests that physiological activation of PTP in aged rats is reduced. Electron microscopy showed alterations of the mitochondrial ultrastructure in tissues from aged rats involving a decreased definition of the cristae and fragmentation of the mitochondrial membranes. We also detected an increase in apoptotic cells in the smooth muscle from aged animals. Our results show that the aging process changes PTP activity, the ability to maintain DeltaPsim and mitochondrial morphology. It is suggested that these can be associated with mitochondrial damage and cell death.     

Mitochondrial alterations and apoptosis in smooth muscle from aged rats

We studied changes in mitochondrial morphology and function in the smooth muscle of rat colon. Under confocal microscopy, tissues loaded with potentiometric dye displayed rapid and spontaneous depolarization. Cyclosporin A (CsA), inhibitor of the permeability transition pore (PTP), caused an increase in mitochondrial membrane potential (ΔΨ_m) in tissues from adult young animals. In aged rats these changes were not observed. This suggests that physiological activation of PTP in aged rats is reduced. Electron microscopy showed alterations of the mitochondrial ultrastructure in tissues from aged rats involving a decreased definition of the cristae and fragmentation of the mitochondrial membranes. We also detected an increase in apoptotic cells in the smooth muscle from aged animals. Our results show that the aging process changes PTP activity, the ability to maintain ΔΨ_m and mitochondrial morphology. It is suggested that these can be associated with mitochondrial damage and cell death.     

Loose-coupled subsarcolemmal mitochondria from muscle Rhomboideus in cold-acclimated piglets

1. Intermyofibrillar (IM) and subsarcolemmal (SM) mitochondria were isolated from rhomboideus (RH) and longissimus dorsi (LD) muscles of cold-acclimated (12 degrees C for 3 weeks) and control (23 degrees C) 8-week-old piglets. 2. Together with measurements of yield of mitochondrial protein and enzyme activities (cytochrome oxydase-CO; creatine kinase--CK), the respiratory rate of isolated mitochondria was followed polarographically in order to determine the respiratory control ratio (RCR) and consequently the tightness of coupling in response to ADP. 3. In control and cold-acclimated piglets, there were more IM than SM (P less than 0.05) and more mitochondria in RH than LD muscle (P less than 0.05). In both muscles, the yield of mitochondria was slightly but not significantly higher after cold acclimation than in controls. 4. In both muscles, IM were tightly coupled and their RCR (congruent to 4.5) were similar in both groups of piglets. RCR values were increased in the presence of bovine serum albumin (BSA). 5. In controls, SM exhibited lower respiration rates than IM (P less than 0.05) and were slightly coupled (RCR congruent to 2). Cold acclimation increases the loose-coupling of SM (P less than 0.05), especially in RH muscle. No changes appeared in the mitochondrial coupling after the addition of BSA. 6. After cold acclimation, CO and CK activities were increased in IM (P less than 0.05) while only CO activity was increased in SM (P less than 0.05). These results support a coupling defect in SM and therefore confirm mitochondrial respiration results.     

Ketone bodies in cold-acclimated rats

Acclimation temperature (28 or 5 degrees C) modifies acetoacetate (AA) and beta-hydroxybutyrate (BOH) levels in blood and liver. In the fed state AA and BOH levels were increased in blood and liver of 5 degrees C adapted rats. In the fasting state (24 or 48 hr) an antiketotic action of cold acclimation was observed. It was found to be more pronounced with high fat diet. These effects were more marked in the blood than in the liver. The variations in ketonemia are discussed with relation to the role of liver in cold adapted rats.     

Autoradiographic detection of triiodothyronine in nuclei from normal and hypothyroid rat liver.

Nuclear triiodothyronine was visualized by light and electron microscope autoradiography of liver nuclei isolated after intraperitoneal injection of [¹²⁵I] triiodothyronine in rats. The nuclear hormone, essentially bound to the putative nuclear triiodothyronine receptor, was found mostly associated with the border of condensed chromatin.     

Mitochondrial damage in galactosamine-induced liver intoxication in rats

Mitichondria isolated from livers of rats which received D-galactosamine (375 mg/kg body wt., four times) demonstrated a marked decrease in respiratory control ratios, the ADP/O ratios, and state 3 respiration rates and an increase in state 4 respiration rates. The aberration was profound with site I being altered prior to sites II and III. Quantitation of phospholipids revealed a reduction of total phospholipids per mg protein with decreases in phosphatidylcholine and phosphatidylethanolamine contents. Caldiolipin was the only phospholipid which remained unaltered. Fatty acid composition was altered in these phospholipids; caldiolipin was altered most severely, showing reductions in linoleic and arachidonic acids, and an elevation in saturated fatty acids and in some other small components of fatty acids. In phosphatidylethanolamine, palmitic acid decreased, whereas stearic and docosahexonoic acids increased. These changes were smaller in phosphatidylcholine fatty acids. These mitochondria were also characterized by an altered composition in high molecular weight polypeptide components. By experiments with normal mitochondria in vitro, galactosamine, but not other aminohexoses, was proved to be an uncoupling agent of the oxidative phosphorylation system. Electron microscopic observation demonstrated that both in vivo and in vitro treatments with galactosamine induced marked disorganization of mitochondral structures. These results suggest that mitochondrial damage is also included in galactosamine-induced hepatic lesion.