Age-related difference in bioenergetics of lung and heart mitochondrial from rats exposed to ozone

Bioenergetics of isolated lung and heart mitochondria from adult and aged rats were examined in the presence of glutamate (NAD-linked substrate) or succinate + rotenone (FAD-linked substrate) following ozone exposure (3.0 ppm, 8 hr). In controls, several differences were observed between adults and aged in both organ preparations. Following exposure, all bioenergetic parameters were decreased significantly in lung preparations from both adult and aged rats. In heart mitochondria, the respiration rates in state 3 and in uncoupled state, and the ADP/O ratio were decreased significantly in both exposed age groups. The respiratory control ratio (RCR) was decreased significantly only in the aged exposed rats. These results suggest that acute exposure to high levels of ozone alters energy production in both lung and heart mitochondria of adult and aged rats.     

Age-related sensitivity to lung oxidative stress during ozone exposure

As immature and aged rats could be more sensitive to ozone (O(3))-linked lung oxidative stress we have attempted to shed more light on age-related susceptibility to O(3) with focusing our interest on lung mitochondrial respiration, reactive oxygen species (ROS) production and lung pro/antioxidant status. For this purpose, we exposed to fresh air or O(3) (500 ppb 12 h per day, for 7 days) 3 week- (immature), 6 month- (adult) and 20 month-old rats (aged). We determined, in lung, H(2)O(2) release by mitochondria, activities of major antioxidant enzymes [superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT)], heat shock protein (HSP(72)) content and 8-oxodG and dG-HNE nDNA contents, as DNA oxidative damage markers. In adult rats we did not observe alteration of pro/antioxidant status. In contrast to adults, immature rats exposed to O(3) higher nDNA 8-oxodG content and HSP(72) and without antioxidant enzymes modification. Aged rats displayed mild uncoupled lung mitochondria, increased SOD and GPx activities, and higher 8-oxodG content after O(3) exposure. Thus, in contrast to adults, immature and aged rats displayed lung oxidative stress after O(3) exposure. Higher sensitivity of immature to O(3) was partly related to ventilatory parameters and to the absence of antioxidant enzyme response. In aged rats, the increase in cytosolic SOD and GPx activities during O(3) exposure was not sufficient to prevent the impairment in mitochondrial function and accumulation in lung 8- oxodG. Finally, we showed that mitochondria seem not to be a major source of ROS under O(3) exposure.     

Effect of ozone exposure on prostacyclin synthesis in lung

The effect of ozone exposure on prostacyclin (PGI2) synthesis in the rat lung was studied. Male Wistar rats were exposed to 0.2, 0.4, 0.8, 1.2 and 1.8 ppm ozone for 24h. The higher concentration (1.8 ppm) significantly depressed-PGI2 synthesizing activity of lung homogenates. Time-courses (1, 3, 5, 7, 14 and 28 days) of the effect of ozone (0.4 and 0.8 ppm) exposure on the PGI2-synthesizing activity of lung homogenates were studied. The PGI2-synthesizing activity of the lung decreased, reaching a maximum at 5 days and then gradually returning to normal by day 14, and remaining normal at day 28, even though the ozone exposure continued. The formation of lipid peroxides due to ozone exposure may cause the depression of PGI2-synthesizing activity of lung. Induction of anti-oxidative enzymes may relate to the recovery of the PGI2-synthesizing activity.     

Ventilatory responses to ozone are reduced in immature rats.

During ozone (O(3)) exposure, adult rats decrease their minute ventilation (VE). To determine whether such changes are also observed in immature animals, Sprague-Dawley rats, aged 2, 4, 6, 8, or 12 wk, were exposed to O(3) (2 ppm) in nose-only-exposure plethysmographs. Baseline VE normalized for body weight decreased with age from 2.1 +/- 0.1 ml. min(-1). g(-1) in 2-wk-old rats to 0. 72 +/- 0.03 ml. min(-1). g(-1) in 12-wk-old rats, consistent with the higher metabolic rates of younger animals. In adult (8- and 12-wk-old) rats, O(3) caused 40-50% decreases in VE that occurred primarily as the result of a decrease in tidal volume. In 6-wk-old rats, O(3)-induced changes in VE were significantly less, and in 2- and 4-wk-old rats, no significant changes in VE were observed during O(3) exposure. The increased baseline VE and the smaller decrements in VE induced by O(3) in the immature rats imply that their delivered dose of O(3) is much higher than in adult rats. To determine whether these differences in O(3) dose influence the extent of injury, we measured bronchoalveolar lavage protein concentrations. The magnitude of the changes in bronchoalveolar lavage induced by O(3) was significantly greater in 2- than in 8-wk-old rats (267 +/- 47 vs. 165 +/- 22%, respectively, P < 0.05). O(3) exposure also caused a significant increase in PGE(2) in 2-wk-old but not in adult rats. The results indicate that the ventilatory response to O(3) is absent in 2-wk-old rats and that lack of this response, in conjunction with a greater specific ventilation, leads to greater lung injury.     

Antioxidative and metabolic responses to extended cold exposure in rats

In this work, we investigated whether extended cold exposure increases oxidative damage and susceptibility to oxidants of rat liver, heart, kidney and lung which are metabolically active tissues. Moreover in this study the effect of cold stress on some of the lipid metabolic mediators were studied in rat experimental model. Male albino Sprague-Dawley rats were randomly divided into two groups: The control group (n=12) and the cold-stress group (n=12). Tissue superoxide dismutase (SOD), catalase (CAT), glutathion S-transferase (GST) and glutathion reductase (GR) activities and glutathion (GSH) were measured using standard protocols. The biochemical analyses for total lipid, cholesterol, trigliceride, HDL, VLDL and LDL were done on autoanalyzer. In cold-stress groups SOD activity was decreased in the lung whereas it increased in the heart and kidney. CAT activity was significantly decreased (except liver) in all the tissues in treated rats. GST activity of cold-induced rats increased in liver and heart while decreased in the lung. GR activity was significantly decreased (except in liver) in all the tissues in cold-stressed rats. GSH level was significantly increased in the heart but decreased in the lung of animals exposed to cold when compared to controls. It was found that among the groups trigliceride, total lipid, HDL and VLDL parameters varied significantly but cholesterol and LDL had no significant variance. In this study, we found that exposure of extended (48 h) cold (8 degrees C) caused changes both in the antioxidant defense system (as tissue and enzyme specific) and serum lipoprotein profiles in rats.     

急性臭氧暴露对大鼠肺部细胞遗传毒性的影响*

目的: 探讨不同浓度臭氧急性暴露对大鼠肺部细胞的遗传毒性的影响。方法: 36只wistar大鼠随机分为对照组(过滤空气暴露)、臭氧暴露组(0.12 ppm、0.5 ppm、1.0 ppm、2.0 ppm、4.0 ppm)共6组,每组6只。以不同浓度的臭氧对大鼠进行动态染毒4 h后,取肺组织并分离单细胞,采用酶联免疫吸附法检测8-羟基脱氧鸟苷(8-OHdG),利用彗星实验、微核试验和DNA-蛋白质交联实验进行DNA和染色体损伤分析。结果: 与对照组相比,肺组织中8-OHdG含量从臭氧暴露浓度为0.12 ppm起即显著增加,在0.5 ppm时达到最高值。随着臭氧暴露浓度升高,彗星拖尾率逐渐上升,且存在明显的剂量-效应关系;DNA-蛋白质交联率有先升高后下降的趋势,且在2.0 ppm时达到最大值;而肺部细胞微核率尽管呈现出上升趋势,但与对照组相比无显著性差异。结论: 急性臭氧暴露在较低浓度(0.12 ppm)时即可导致大鼠肺部细胞的DNA损伤;而在较高浓度(4 ppm)时却未见显著的染色体损伤。     

Increased vitamin E content in the lung after ozone exposure: a possible mobilization in response to oxidative stress

Vitamin E (vE) is a biological free radical scavenger capable of providing antioxidant protection depending upon its tissue content. In previous studies, we observed that vE increased significantly in rat lungs after oxidant exposure, and we postulated that vE may be mobilized to the lung from other body sites under oxidative stress. To test this hypothesis, we fed Long-Evans rats either a vE-supplemented or a vE-deficient diet, injected them intraperitoneally with 14C-labeled vE, and then exposed half of each group to 0.5 ppm ozone (O3) for 5 days. After exposure, we determined vE content and label retention in lungs, liver, kidney, heart, brain, plasma, and white adipose tissue. Tissue vE content of all tissues generally reflected the dietary level, but labeled vE retention in all tissues was inversely related to tissue content, possibly reflecting a saturation of existing vE receptor sites in supplemented rats. Following O3 exposure, lung vE content increased significantly in supplemented rats and decreased in deficient rats, but the decrease was not statistically significant, and vE content remained unchanged in all other tissues of both dietary groups. Retention of 14C-labeled vE increased in all tissues of O3-exposed rats of both dietary groups, except in vE-deficient adipose tissue and vE-supplemented brain, where it decreased, and plasma, where it did not change. The marked increases in lung vE content and labeled vE retention of O3-exposed vE-supplemented rats support our hypothesis that vE may be mobilized to the lung in response to oxidative stress, providing that the vitamin is sufficiently available in other body sites.     

Effect of chronic ethanol consumption on energy-linked processes associated with oxidative phosphorylation: Proton translocation and ATP-Pi exchange

Male rats were administered an ethanol-containing diet for 31 days during which time they demonstrated fatty liver. Mitochondria and submitochondrial particles were prepared from their livers (ethanol mitochondria, ethanol submitochondrial particles) and from their pair-fed partners (control mitochondria, control submitochondrial particles). The H⁺/coupling site ratio was not significantly different in ethanol and control mitochondria with succinate as electron donor. A 13% decrease in the H⁺/coupling site ratio was observed in ethanol mitochondria, however, when β-hydroxybutyrate was used as substrate. The rate of ATP-P_i exchange was decreased significantly in both ethanol mitochondria and submitochondrial particles as compared to control preparations. These observations demonstrate ethanol-elicited decreases in energy conservation in the site I region of the electron transport chain and in the activity of the ATP synthetase complex.     

Exposure to intermittent high altitude induces different changes in adenylyl cyclase activity in hearts of young and adult Wistar rats

This study investigates changes of adenylyl cyclase activity in the heart of young and adult Wistar rats exposed to experimental conditions simulating high altitude hypoxia as a model for interpretation of some adaptive changes of adenylyl cyclase observed in human. The exposure of rats to intermittent high altitude (IHA) hypoxia (5000 m) showed significant adaptive changes. The right ventricular weight and the ratio of right/left ventricular weights of adult rats exposed to IHA were significantly increased when compared to appropriate controls; adaptive changes of cardiac adenylyl cyclase being dependent on the age of the animals. The isoprenaline-stimulated activity was higher in the left than in the right ventricle, and in both ventricles it was higher in young rats than in adult rats. When compared to controls, isoprenaline stimulation was decreased in the right ventricles of adapted young rats and, by contrast, it was increased in the left ventricles of adapted adult rats. This decrease and increase of adenylyl cyclase activity evoked by isoprenaline was paralleled by forskolin-induced adenylyl cyclase activity in these experimental groups. It seems therefore that the changes in the pattern of total adenylyl cyclase activity observed under IHA hypoxia may at least be partially explained by the changes of beta-adrenergic receptor susceptibility following IHA hypoxia.     

臭氧亚慢性暴露对大鼠心脏lncRNA表达谱的影响*

目的: 观察臭氧亚慢性暴露后大鼠心脏中lncRNA表达变化,为探索lncRNA在臭氧亚慢性暴露致心脏损伤中的作用与机制提供科学数据。方法: 将18只Wistar大鼠随机分为清洁空气组和臭氧暴露组,每组9只,置于气体染毒柜中,清洁空气组吸入过滤空气,而臭氧暴露组吸入含0.5 ppm(0.980 mg/m³)臭氧的混合气体,每天6 h,持续90 d。染毒结束后取心脏组织并提取总RNA,利用大鼠lncRNA芯片和qRT-PCR技术检测大鼠心脏中lncRNA表达量,并通过生物信息学方法分析差异表达lncRNA的潜在功能。结果: 与清洁空气组相比,臭氧暴露组大鼠心脏中lncRNA表达谱发生改变,其中167个显著上调,64个显著下调;GO分析提示显著上调的lncRNA主要参与生长发育,显著下调的lncRNA主要参与调节营养物质分解代谢;KEGG分析表明显著上调的lncRNA主要参与调控PI3K-Akt信号通路,显著下调的lncRNA主要参与调控多种维生素和主要供能物质的代谢过程。结论: 臭氧亚慢性暴露可致大鼠心脏lncRNA表达谱发生变化,差异表达的lncRNA可能通过影响心脏中能量和营养物质代谢在臭氧亚慢性暴露致心脏损伤中发挥作用。     

The influence of maternal nicotine exposure on the interalveolar septal status of neonatal rat lung.

The aim of this study was to determine the effect of maternal nicotine exposure (1 mg nicotine/kg body mass/day, subcutaneously) on the status of the alveolar septa of the 1 to 21 day old offspring. The data obtained showed swelling of type II and interstitial cell mitochondria. The type I:type II cell ratio decreased as a result of type II cell proliferation. The number of capillaries per unit length of septum was also significantly lower than that of control lung. Ruptured blood-air barriers also occur in the nicotine exposed lungs of rats of all age groups. The results show that maternal nicotine exposure interfered with the morphometric and morphologic characteristics of the septa of lung tissue of the offspring.     

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.     

Ozone increases amino- and carboxy-terminal atrial natriuretic factor prohormone peptides in lung,heart, and circulation

Ozone can cause pulmonary edema and simultaneously decrease blood pressure. Atrial natriuretic peptides may mediate both of these effects in that they increase pulmonary capillary permeability resulting in edema formation and are potent vasodilating peptides. To examine this possibility, the lungs of Fischer 344 rats were exposed to ozone (0.5 ppm) for 8 hours which resulted in a three- to fourfold increase in atrial natriuretic peptides. Ozone also increased atrial natriuretic peptides in the heart two- to fivefold from 266 ± 25, 226 ± 22, and 288 ± 40 ng/g (room air) to 716 ± 26, 471 ± 14, and 1473 ± 235 ng/g recognized by the proANFs 1–30 and 31–67 and atrial natriuretic factor radioimmunoassays, respectively. Ozone also doubled the concentrations of proANFs 1–30, 31–67, and 1–98 and ANF in the circulation. This study demonstrates that ozone increases atrial natriuretic peptides within the heart, lung, and circulation, suggesting that atrial natriuretic peptides may mediate the decreased blood pressure and pulmonary edema observed with ozone exposure. Since the proANF 31–67 radioimmunoassay exclusively recognizes the ANF prohormone within the heart, this study further indicates that ozone can increase the synthesis of the ANF prohormone.     

Ketone-body metabolism in hyperthyroid rats: reduced activity of D-3-hydroxybutyrate dehydrogenase in both liver and heart and of succinyl-coenzyme A: 3-oxoacid coenzyme A-transferase in heart

The specific activity of D-3-hydroxybutyrate dehydrogenase is reduced by about a third in liver and heart mitochondria of hyperthyroid rats. State 3 respiration is also reduced in isolated mitochondria from the same animals when DL-3-hydroxybutyrate is the substrate. Determination of the kinetic parameters of the membrane-bound D-3-hydroxybutyrate dehydrogenase in liver of hyperthyroid rats reveals a decreased in maximal velocity (Vmax). The Michaelis and dissociation constants of NAD+ and D-3-hydroxybutyrate are also significantly influenced, thus indicating that both the affinity and the binding of this enzyme toward its substrates are affected. In hyperthyroid rats a significant ketone-body increase is found in both liver and heart: in blood, an almost doubled concentration can be measured. At the same time, in heart mitochondria of these animals the activity of succinyl-coenzyme A: 3-oxoacid coenzyme A-transferase is significantly reduced. The decrease in both D-3-hydroxybutyrate dehydrogenase and 3-oxoacid coenzyme A-transferase associated with the increase in ketone bodies supports the suggestion that there is a lower utilization of these compounds by peripheral tissues. In the blood of hyperthyroid rats a higher D-3-hydroxybutyrate/acteoacetate ratio is also found, probably resulting from a selective utilization of the two compounds in this pathological state.     

The role of the matrix calcium level in the enhancement of mitochondrial pyruvate carboxylation by glucagon pretreatment.

The effect of Ca2+ on the rate of pyruvate carboxylation was studied in liver mitochondria from control and glucagon-treated rats, prepared under conditions that maintain low Ca2+ levels (1-3 nmol/mg of protein). When the matrix-free [Ca2+] was low (less than 100 nM), the rate of pyruvate carboxylation was not significantly different in mitochondria from control and glucagon-treated rats. Accumulation of 5-8 nmol of Ca2+/mg, which increased the matrix [Ca2+] to 2-5 microM in both preparations, significantly enhanced pyruvate carboxylase flux by 20-30% in the mitochondria from glucagon-treated rats, but had little effect in control preparations. Higher levels of Ca2+ (up to 75 nmol/mg) inhibited pyruvate carboxylation in both preparations, but the difference between the mitochondria from control and glucagon-treated animals was maintained. The enhancement of pyruvate dehydrogenase flux by mitochondrial Ca2+ uptake was also significantly greater in mitochondria from glucagon-treated rats. These differential effects of Ca2+ uptake on enzyme fluxes did not correlate with changes in the mitochondrial ATP/ADP ratio, the pyrophosphate level, or the matrix volume. Arsenite completely prevented 14CO2 incorporation when pyruvate was the only substrate, but caused only partial inhibition when succinate and acetyl carnitine were present as alternative sources of energy and acetyl-CoA. Under these conditions, mitochondria from glucagon-treated rats were less sensitive to arsenite than the control preparations, even at low Ca2+ levels. We conclude that the Ca(2+)-dependent enhancement of pyruvate carboxylation in mitochondria from glucagon-treated rats is a secondary consequence of pyruvate dehydrogenase activation; glucagon treatment is suggested to affect the conditions in the mitochondria that change the sensitivity of the pyruvate dehydrogenase complex to dephosphorylation by the Ca(2+)-sensitive pyruvate dehydrogenase phosphatase.     

Exposure to Intermittent High Altitude Induces Different Changes in Adenylyl Cyclase Activity in Hearts of Young and Adult Wistar Rats

Abstract

This study investigates changes of adenylyl cyclase activity in the heart of young and adult Wistar rats exposed to experimental conditions simulating high altitude hypoxia as a model for interpretation of some adaptive changes of adenylyl cyclase observed in human. The exposure of rats to intermittent high altitude (IHA) hypoxia (5000 m) showed significant adaptive changes. The right ventricular weight and the ratio of right/left ventricular weights of adult rats exposed to IHA were significantly increased when compared to appropriate controls; adaptive changes of cardiac adenylyl cyclase being dependent on the age of the animals. The isoprenaline‐stimulated activity was higher in the left than in the right ventricle, and in both ventricles it was higher in young rats than in adult rats. When compared to controls, isoprenaline stimulation was decreased in the right ventricles of adapted young rats and, by contrast, it was increased in the left ventricles of adapted adult rats. This decrease and increase of adenylyl cyclase activity evoked by isoprenaline was paralleled by forskolin‐induced adenylyl cyclase activity in these experimental groups. It seems therefore that the changes in the pattern of total adenylyl cyclase activity observed under IHA hypoxia may at least be partially explained by the changes of beta‐adrenergic receptor susceptibility following IHA hypoxia.     

Biomarkers of Oxidative Stress Study IV: ozone exposure of rats and its effect on antioxidants in plasma and bronchoalveolar lavage fluid

The objective of this study was to determine whether acutely exposing rats to ozone would result in the loss of antioxidants from plasma and bronchoalveolar lavage fluid (BALF). Additional goals were to compare analyses of the same antioxidant concentration between different laboratories, to investigate which methods have the sensitivity to detect decreased levels of antioxidants, and to identify a reliable measure of oxidative stress in ozone-exposed rats. Male Fisher rats were exposed to either 2.0 or 5.0 ppm ozone inhalation for 2 h. Blood plasma and BALF samples were collected 2, 7, and 16 h after the exposure. It was found that ascorbic acid in plasma collected from rats after the higher dose of ozone was lower at 2 h, but not later. BALF concentrations of ascorbic acid were decreased at both 2 and 7 h postexposure. Tocopherols (α, δ, γ), 5-nitro-γ-tocopherol, tocol, glutathione (GSH/GSSG), and cysteine (Cys/CySS) were not decreased, regardless of the dose or postexposure time point used for sample collection. Uric acid was significantly increased by the low dose at 2 h and the high dose at the 7 h point, probably because of the accumulation of blood plasma in the lung from ozone-increased alveolar capillary permeability. We conclude that measurements of antioxidants in plasma are not sensitive biomarkers for oxidative damage induced by ozone and are not a useful choice for the assessment of oxidative damage by ozone in vivo.     

Oscillatory mechanics of the respiratory system in ozone-exposed rats

The respiratory system impedance of tracheostomized cardiorespiratory disease-free Sprague-Dawley rats was measured from 20 to 90 Hz at constant flow amplitudes in 10 rats exposed to 0.64 ppm (UV) ozone for 7 days, and eight rats exposed to the same level of ozone for 20 days. This data was compared with respiratory system impedence spectra of 24 normal rats obtained in the same manner. When compared with control, the real part (effective resistance) was significantly different at several frequencies in the 7-day group (P less than 0.05), and group means were higher at all frequencies. The 20-day group showed no significant differences in effective resistance. The imaginary part (effective reactance) was significantly lower at higher frequencies (f greater than 36) in both exposure groups (P less than 0.05). When the impedance curves for each individual were fit to a lumped six-parameter model, and the parameters were compared, only the peripheral resistance parameter of the 7-day group was significantly different from control (P less than 0.05). We conclude that ozone exposure at this level causes changes in respiratory system impedance, that these changes consist primarily of decreased reactances at higher frequencies, and that at 7 days these changes can be modeled by an increase in peripheral resistance.     

Influence of vitamin E on polyamine metabolism in ozone-exposed rat lungs

The influence of vitamin E (E) on lung polyamine metabolism of rats exposed to ozone (O3) was examined. Rats fed diets wither E-deficient or supplemented with 1000 IU E/kg were exposed to 0.5 +/- 0.05 ppm O3 or filtered room air continuously for 5 days. They were then sacrificed and their lungs were analyzed for biochemical changes. Lung E content was strongly associated with the dietary level, and increased (36%, P less than 0.05) after O3 exposure only in E-supplemented rats. Lung polyamine metabolism was not affected in the air-control rats by E level, but increased after O3 exposure in both dietary groups. The activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase were elevated above air controls. However, the increases were significant only for E-deficient rats when compared to E-supplemented rats. After O3 exposure, putrescine increased significantly in both dietary groups; spermidine increased but was significantly higher only in the E-deficient group; and spermine remained unchanged in both dietary groups. Elevated E content of supplemented rat lungs after O3 exposure may represent its mobilization under oxidant stress. Increased polyamine metabolism of E-deficient rats suggests either a greater sensitivity to injury by O3 or a possible antioxidant function for polyamines compensating for E deficiency.     

The effect of aging and acetyl-L-carnitine on the pyruvate transport and oxidation in rat heart mitochondria.

The effect of aging and acute treatment with acetyl-L-carnitine on the pyruvate transport and oxidation in rat heart mitochondria was studied. The activity of the pyruvate carrier as well as the rates of pyruvate-supported respiration were both depressed (around 40%) in heart mitochondria from aged rats, the major decrease occurring during the second year of life. Administration of acetyl-L-carnitine to aged rats almost completely restored the rates of these metabolic functions to the level of young control rats. This effect of acetyl-L-carnitine was not due to changes in the content of pyruvate carrier molecules. The heart mitochondrial content of cardiolipin, a key phospholipid necessary for mitochondrial substrate transport, was markedly reduced (approximately 40%) in aged rats. Treatment of aged rats with acetyl-L-carnitine reversed the age-associated decline in cardiolipin content. As the changes in cardiolipin content were correlated with changes in rates of pyruvate transport and oxidation, it is suggested that acetyl-L-carnitine reverses the age-related decrement in the mitochondrial pyruvate metabolism by restoring the normal cardiolipin content.