Wfs1-deficient animals have brain-region-specific changes of Na+, K+-ATPase activity and mRNA expression of α1 and ß1 subunits.

Mutations in the WFS1 gene, which encodes the endoplasmic reticulum (ER) glycoprotein, cause Wolfram syndrome, a disease characterized by juvenile-onset diabetes mellitus, optic atrophy, deafness, and different psychiatric abnormalities. Loss of neuronal cells and pancreatic ß-cells in Wolfram syndrome patients is probably related to the dysfunction of ER stress regulation, which leads to cell apoptosis. The present study shows that Wfs1-deficient mice have brain-region-specific changes in Na(+),K(+)-ATPase activity and in the expression of the α1 and ß1 subunits. We found a significant (1.6-fold) increase of Na-pump activity and ß1 subunit mRNA expression in mice lacking the Wfs1 gene in the temporal lobe compared with their wild-type littermates. By contrast, exposure of mice to the elevated plus maze (EPM) model of anxiety decreased Na-pump activity 1.3-fold in the midbrain and dorsal striatum and 2.0-fold in the ventral striatum of homozygous animals compared with the nonexposed group. Na-pump α1 -subunit mRNA was significantly decreased in the dorsal striatum and midbrain of Wfs1-deficient homozygous animals compared with wild-type littermates. In the temporal lobe, an increase in the activity of the Na-pump is probably related to increased anxiety established in Wfs1-deficient mice, whereas the blunted dopamine function in the forebrain of Wfs1-deficient mice may be associated with a decrease of Na-pump activity in the dorsal and ventral striatum and in the midbrain after exposure to the EPM.

The effects of different antioxidants on the activity of cerebrocortical MnSOD and Na,K-ATPase from post mortem Alzheimer's disease and age-matched normal brains.

Among the markers and targets of the early phase of Alzheimer's disease (AD) pathogenesis MnSOD (mitochondrial dysfunction) and Na-pump (disturbances in function/regulation) are often highlighted. This paper focused on comparison of the effects of three antioxidants on the activity of cerebrocortical MnSOD and Na,K-ATPase from post mortem Alzheimer's disease and age-matched normal brains. Antioxidant compounds with different origins: natural glutathione, synthetic UPF peptides (glutathione analogues) and phytoestrogen genistein were investigated. Firstly, MnSOD and Na,K-ATPase activities were found to be decreased in the post mortem AD brains compared with age-matched controls. Secondly, GSH had no effect on MnSOD activity, but decreased Na,K-ATPase activity both in the control and AD brains. Thirdly, UPF1 and UPF17 increased MnSOD activity, and UPF17 suppressed Na,K-ATPase activity. Further studies are needed to clarify, if the inhibitory effect of UPF17 on Na,K-ATPase could abolish the beneficial effect gained from MnSOD activation. Both the antioxidative potential of genistein and its potency to up-regulate Na,K-ATPase activity make it an attractive candidate substance to suppress the early phase of the pathogenesis of AD.

Temperature dependence of the sodium pump is altered in the cerebral cortex of CCK2 receptor-deficient mice.

Previously we have shown that the temperature dependence of the sodium pump (Na(+),K(+)-ATPase) is altered under different neuropathological conditions. In this study we compared temperature dependence of the Na(+),K(+)-ATPase in the fronto-parietal cortex of CCK(2) receptor-deficient (homo- and heterozygous) and normal (wild-type) mice. The Arrhenius plot for Na(+),K(+)-ATPase from wild-type brain is non-linear with a breakpoint at 20.3 +/- 0.4 degrees C. In case of the brain cell membrane of CCK(2) receptor-deficient mice (homo- and heterozygous) the breakpoint on Arrhenius plot was detected at 26.0 +/- 1.1 degrees C and 25.4 +/- 0.4 degrees C, respectively. The shift of the breakpoint on the Arrhenius plot established in CCK(2) receptor-deficiency as well as in case of some other pathological conditions confirms that such kind of alteration in the Na(+),K(+)-ATPase temperature dependence is likely related to the homeostatic adjustment of altered function of the sodium pump.

Clear differences in adiponectin level and glutathione redox status revealed in obese and normal-weight patients with psoriasis.

BACKGROUND: Several studies have shown increased prevalence of obesity in patients with psoriasis. OBJECTIVES: To characterize both inflammatory- and oxidative stress-related differences between obese patients with psoriasis (OPP) and normal-weight patients with psoriasis (NWPP). METHODS: The plasma concentrations of adiponectin and interleukin (IL)-6 were analysed by quantitative sandwich enzyme immunoassay technique in 10 patients with a body mass index (BMI)<25 and 12 patients with a BMI>30. Total glutathione and oxidized glutathione levels were measured spectrophotometrically. RESULTS: Plasma concentration of adiponectin in NWPP was more than twice the level in healthy normal-weight controls (P<0.001), while such an elevation did not occur in OPP. OPP were characterized by a significantly increased IL-6 level, which correlated negatively with the adiponectin level (r=-0.85, P<0.001). The glutathione redox status, which was also inversely correlated with the adiponectin level (r=-0.63, P<0.05), was associated with significantly increased oxidative stress in the OPP compared with the NWPP or controls. CONCLUSIONS: Obesity in patients with psoriasis is associated with both decreased plasma levels of protective adiponectin compared with NWPP, and enhanced systemic inflammation and oxidative stress. These findings are in concordance with high prevalence of diseases related to lower adiponectin levels among psoriasis patients.

Homocysteine status in former top-level male athletes: possible effect of physical activity and physical fitness.

The importance of elevated homocysteine (Hcy) as a risk marker for cardiovascular disease is continuously under debate. Lifestyle factors may increase the total Hcy (tHcy) level of the plasma, but there are no consistent findings relating to Hcy, physical activity, and cardiorespiratory fitness. Cross-sectional measurement from an ongoing follow-up study was performed on 77 former male athletes and 33 sedentary controls (age range 35-62 years). Lifestyle parameters (current physical activity patterns, smoking, etc.), anthropometric and blood pressure data, and data about tHcy, reduced, and oxidized glutathione (GSH, GSSG, respectively) in blood, lipoproteins, and maximal oxygen consumption (VO(2max)) were collected. Our study results showed that the subgroup of physically active ex-athletes (n=52) had a significantly lower tHcy level and glutathione redox ratio (GSSG:GSH) in comparison with the subgroup of sedentary ex-athletes (n=25). tHcy level was inversely related to cardiorespiratory fitness (VO(2max)/kg). Dietary and smoking habits were not significantly associated with the tHcy level in our study group. In conclusion, the research findings indicate that both current physical activity and cardiorespiratory fitness are significantly inversely associated with an elevated homocysteine level in middle-aged former athletes.

Pre-treatment with hyperoxia before coronary artery bypass grafting - effects on myocardial injury and inflammatory response.

BACKGROUND: In experimental studies, exposure to hyperoxia for a limited time before ischaemia induces a low-grade systemic oxidative stress and evokes an (ischaemic) preconditioning-like effect of the myocardium. We hypothesised that hyperoxia before cardioplegia could protect the myocardium against necrosis and stunning caused by ischaemia-reperfusion. METHODS: Forty patients undergoing coronary artery bypass grafting were randomly exposed to an oxygen fraction of 0.4 or > 0.96 in inspired air on an average of 120 min before cardioplegia. Blood for troponin I, creatine kinase-MB, lactate, glutathione and interleukin-6 was sampled from arterial and coronary sinus cannulae during 20 min of reperfusion. Additional arterial samples were drawn 60 min after declamping and in the first post-operative morning. The cardiac index and right and left ventricular stroke work indices were measured before sternotomy and up to 12 h post-operatively. RESULTS: Troponin I, creatine kinase-MB and lactate did not differ between the groups. Hyperoxic pre-treatment had no impact on the post-operative haemodynamic indices measured with the thermodilution pulmonary artery catheter. More oxidised glutathione was released in the hyperoxia group in the first minute of reperfusion (P = 0.015). Hyperoxic pre-treatment abolished the myocardial release of interleukin-6 during 20 min of reperfusion (P = 0.021 vs. controls). In the first post-operative morning, interleukin-6 was higher in the hyperoxia group [127.0 (86.0-140.0) vs. 85.2 pg/ml (66.6-94.5 pg/ml); P = 0.016]. CONCLUSIONS: Exposure to >96% oxygen before cardioplegia did not attenuate ischaemia-reperfusion injury of the heart in patients undergoing coronary artery bypass grafting. The only potentially beneficial effect observed was the decreased transmyocardial release of interleukin-6.

Atherogenic inflammatory and oxidative stress markers in relation to overweight values in male former athletes.

OBJECTIVE: To evaluate inflammation- and oxidative stress-related (OxS) background in former athletes in relation to overweight and abdominal obesity status. DESIGN: Cross-sectional data from ongoing follow-up study. SUBJECTS: A total of 60 middle-aged former athletes (46.6+/-7.5 years; 181.1+/-7.2 cm; 88.1 +/- 12.9 kg) and 54 age-matched controls (48.1+/-7.3 years; 181.4 +/- 6.2 cm; 89.7 +/- 14.4 kg). MEASUREMENTS: Anthropometric characteristics, serum lipoproteins (CHOL, HDL-C, LDL-C, TG), oxidized LDL (oxLDL), diene conjugates (DC) and high-sensitive C-reactive protein (hsCRP). Information about the physical activity and other lifestyle variables were collected by the questionnaire. RESULTS: Ex-athletes were characterized by significantly higher physical activity characteristics and lower CHOL and oxLDL in comparison with controls. Correlation analysis among ex-athletes revealed negative associations between all measured overweight data (body mass index, fat percentage, waist to hip circumferences and waist circumference (WC)), and current physical activity. Current physical activity was significantly related to OxS and inflammatory characteristics (oxLDL, DC and hsCRP) among the ex-athletes, but not among the control group. The most expressed positive correlations were found between WC, hsCRP, triglycerides (TG), DC and oxLDL in both study groups. CONCLUSION: Our study results suggest that there exists an independent (adjusted for potential confounders) association between overweight, abdominal obesity, and atherogenic inflammatory and oxidative stress markers in ex-athletes as well as in age-matched controls. Major findings of our study show that WC is the best correlate of hsCRP, oxLDL, DC and TG levels.

High-sensitive C-reactive protein level and oxidative stress-related status in former athletes in relation to traditional cardiovascular risk factors.

OBJECTIVE: To analyze systemic and cellular oxidative stress-related indices as well as C-reactive protein level in former top-level athletes in relation to traditional cardiovascular risk factors. METHODS: A cross-sectional study was performed in 53 former male athletes and 25 sedentary controls (age range: 39-59 years). We measured anthropometric factors (BMI, fat percentage, WHR), resting blood pressure (SBP, DBP), serum cholesterol (CHOL), high-density lipoprotein-cholesterol (HDL-C), low-density lipoprotein-cholesterol (LDL-C), triglycerides (TG), total antioxidant status (TAS), oxidized LDL-C (oxLDL), diene conjugates (DC), glutathione redox status, high-sensitive C-reactive protein (hsCRP), and leisure-time physical activity. RESULTS: Physically active former athletes had significantly lower mean overweight (BMI, fat percentage, WHR), better spectrum of atherogenesis indicators (CHOL, HDL-C, TG, TG:HDL-C ratio) and lower oxidative stress (oxLDL, oxLDL:LDL-C ratio, DC) values than sedentary ex-athletes. No significant differences in these variables were found between the sedentary ex-athletes and control group. Significant associations were found between physical activity (METs), SBP, DBP, hypertension, CHOL, HDL-C, TG, TG:HDL-C ratio, oxLDL, oxLDL:LDL-C ratio, DC and hsCRP. CONCLUSIONS: A physically active lifestyle is related to a lower cardiovascular disease (CVD) risk profile including a substantially lower systemic and cellular oxidative stress status as well as C-reactive protein level in middle-aged men.

Is elective abdominal aortic aneurysm repair accompanied by high grade oxidative stress?

BACKGROUND AND AIMS: During elective abdominal aortic aneurysm repair (AAAR), lower torso ischaemia-reperfusion event is unavoidable. Previous studies on AAAR have reported the importance of oxidative stress (OS) in ischaemia-reperfusion injury, however, the grade of OS has not been adequately clarified up to now. The aim of this study was to perform a complex investigation of the time-course and grade of systemic and cellular OS in patients undergoing AAAR. MATERIAL AND METHODS: Arterial blood samples were taken from 18 patients undergoing elective AAAR (at four points in time: before anaesthesia, 5 min after aortic clamping and 5 min and 30 min after clamp removal). Diene conjugates (DC), thiobarbituric acid reactive substances (TBARS), total antioxidative capacity (TAC), glutathione redox ratio (GSSG/GSH), and levels of antioxidative enzymes as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSHPx) were measured from the radial arterial blood. RESULTS: 30 min after the removal of the aortic cross-clamp, arterial CAT showed significant elevation (96.0 vs 56.9 U/l, p < 0.05); GSHPx was significantly elevated (51.5 vs 39.9 U/g Hgb, p < 0.05) and TAC was decreased (31.4 vs 36.5%, p < 0.05) in comparison with preoperative value. CONCLUSIONS: We found limited alterations of several OS parameters, which do not characterize either systemic or cellular high-grade OS during elective AAAR.

The cerebrocortical areas in normal brain aging and in Alzheimer's disease: noticeable differences in the lipid peroxidation level and in antioxidant defense.

The markers of oxidative stress were measured in four cerebrocortical regions of Alzheimer's disease (AD) and age-matched control brains. In controls the levels of diene conjugates (DC) and lipid peroxides (LOOH) were significantly higher in the sensory postcentral and occipital primary cortex than in the temporal inferior or frontal inferior cortex. The antioxidant capacity (AOC) was highest in the temporal, and GSH in the frontal inferior cortex. The highest activity of superoxide dismutase (SOD) and catalase (CAT) was found in the occipital primary cortex. Compared with controls, significantly higher level of DC and LOOH and attenuated AOC were evident in AD temporal inferior cortex. In AD frontal inferior cortex moderate increase in LOOH was associated with positive correlation between SOD activity and counts of senile plaques. Our data suggest that in AD cerebral cortex, the oxidative stress is expressed in the reducing sequence: temporal inferior cortex > frontal inferior cortex > sensory postcentral cortex approximately = occipital primary cortex, corresponding to the histopathological spreading of AD from the associative to primary cortical areas.

Pretreating rats with hyperoxia attenuates ischemia-reperfusion injury of the heart.

Oxidative stress may precondition the heart. The present study investigated whether hyperoxia elicits a preconditioning-like response. Rats were kept in a hyperoxic (>95% O2) environment for 60 or 180 minutes. Hearts were Langendorff-perfused immediately or 24 hours after hyperoxia, and exposed to 25 minutes of global ischemia and 60 minutes of reperfusion. Whole blood was sampled after 60 and 180 minutes of hyperoxia for oxidative stress markers. Hearts were sampled immediately or 24 hours after hyperoxia for measurement of antioxidants, lipid peroxidation products, heat shock protein 72 and endothelial nitric oxide synthase. At the end of reperfusion after 1 h hyperoxia, infarct size was determined by tetrazolium staining. Hyperoxia increased serum levels of conjugated dienes, reduced serum antioxidative protection, reduced reperfusion arrhythmias in most groups, and improved myocardial function. Infarct size was reduced from 45% of myocardial tissue in controls to 22% in treated animals. The myocardial activity of antioxidant enzymes, content of heat shock protein 72, and endothelial nitric oxide synthase in myocardial tissue were not influenced. In conclusion, hyperoxia induces a low-graded systemic oxidative stress, improves postischemic cardiac function and reduces infarct size. The mediators of protection remain to be determined.

Acute immune response in respect to exercise-induced oxidative stress.

The relationship between exhaustive exercise, oxidative stress, the protective capacity of the antioxidant defense system and cellular immune response has been determined. Exhaustive exercise in well-trained young men (n=19)-induced leukocytosis, decreased proportion of activated-lymphocyte subsets (CD4+ and CD8+) expressing CD69, decreased lymphocyte mitogenic response to concanavalin A (ConA) and phytohemagglutinin (PHA), increased lipid peroxidation, increased total antioxidant status (TAS) and catalase activity, immediately after exercise. Suppressed blood concentration of T-lymphocyte subsets (CD3+, CD4+, CD8+, NK), increased TAS and blood total glutathione (TGSH) in early recovery period (30 min after exercise) were found. Strong positive correlation was observed between TGSH and lymphocyte mitogenic response to ConA and PHA (r=0.85 and 0.85, respectively) immediately after exercise. Moderate positive correlation was observed between TAS and lymphocyte mitogenic response to PHA (r=0.59) immediately after exercise as well as between TAS and lymphocyte mitogenic response to PHA and ConA (r=0.69 and 0.54, respectively). Moderate to weak correlation was observed between TAS and conjugated dienes with exercise (r=0.66) as well as in 30-min recovery (r=0.50). After a short-term bout of exhaustive exercise, immune system was characterized by acute phase response, which was accompanied with oxidative stress. Suppression of the cellular immunity 30 min after exercise shows that this period is not enough for recovery after exhaustive exercise. The results suggest the interactions between exercise-induced oxidative stress and immune response.

Pretreatment with methylprednisolone protects the isolated rat heart against ischaemic and oxidative damage.

Methylprednisolone (MP), a synthetic glucocorticoid, is widely used clinically and experimentally as acute antiinflammatory treatment. The molecular actions of MP indicate that pretreatment with this drug may be cardioprotective. We investigated if giving rats MP prior to excising their hearts for Langendorff-perfusion protected cardiac function against oxidative stress, and if this was mediated by increasing antioxidant defence or influencing myocardial nitric oxide synthase (NOS). Rats (n=6-11 in each group) were injected with MP (40mg/kg i.m.) or vehicle 24 and 12 h before Langendorff-perfusion with 30 min global ischaemia and 60 min reperfusion, or 10 min perfusion with 180 micromol/L hydrogen peroxide. Other hearts were exposed to 30 min global ischaemia 5 days after MP-injection. Additional hearts were sampled before, during, and after ischaemia for analyzing tissue activity of antioxidant enzymes. Tissue endothelial and inducible NOS (eNOS and iNOS) were investigated by immunoblotting and semiquantitative RT-PCR in a time-course after MP injection. Pretreatment with MP improved left ventricular function and increased coronary flow during postischaemic reperfusion, and this effect was sustained 5 days afterwards. When exposing hearts to hydrogen peroxide, MP improved coronary flow. Catalase, glutathione peroxidase, and oxidized glutathione were increased during reperfusion of MP-treated hearts compared to vehicle only. MP did not influence eNOS at protein or mRNA level. iNOS could not be detected by immunoblotting, indicating low cardiac enzyme content. Its mRNA initially increased the first hour after injection, thereafter decreased. In conclusions, pretreating rats with MP protects the heart against ischaemia-reperfusion dysfunction. This effect could be due to increase of tissue antioxidant activity during reperfusion. MP did not influence cardiac eNOS. mRNA for iNOS was influenced by MP, but the corresponding protein could not be detected.

Effect of low-dose aspirin on the markers of oxidative stress.

UNLABELLED: The present study estimates effects of low-dose enteric coated aspirin (ECA) on oxidative stress (OS) markers in a group of middle-aged men (mean age 51.2 +/- 6.9 years) free of pre-existing ischemic heart disease. METHODS: Serum products of lipid peroxidation, and measures of antioxidative status were detected in 25 healthy men in baseline and after two-week treatment period. RESULTS: In respect to serum products of lipid peroxidation and markers of antioxidant status, no statistically significant differences between the pre- and after-treatment data were observed for any measures, with the exception of values of serum antioxidative capacity (39.0 +/- 2.5 and 42 +/- 4.6, respectively). CONCLUSIONS: Administration of ECA does not initiate the OS in blood and improves the general antioxidative potency of blood. This may imply towards certain antiatherogenic influence of low-dose ECA, exhibited even with a short-term treatment period. Regarding OS markers, a variety of individual responses observed in the selected subgroups should be investigated and possibly taken into account while treatment with ECA is initiated for primary prevention of cerebrovascular events.

Attempt to solubilize Na+/K+-exchanging ATPase with amphiphilic peptide PD1.

The effect of the 24-amino-acid-long peptide, PD(1), on rat cerebral cortical Na+/K+ -exchanging ATPase (EC 3.6.1.37) has been studied. Incubation of the enzyme preparation (25 degrees C for 10-25 min) with the peptide (10(-7) - 10(-4) M) did not appreciably affect the activity of the enzyme, only 5-8% activation being registered. On the other hand, PD(1) completely eliminated the cooperative nature of Na+ -binding to Na+/K+ -exchanging ATPase (n(H) decreased from 1.4 to 0.9) and slightly (1.2-fold) decreased the affinity for Na+. ATP, a substrate of activity for Na+/K+ -exchanging ATPase, blocked the PD(1)-promoted effect on the cooperativity for Na+. Incubation of cerebral cortical membranes with 5 x 10(-4) M PD(1) revealed a shift (from 19.5 degrees C to 21.4 degrees C) of the typical break on the Arrhenius plot (15-37 degrees C). Prolonged incubation of enzyme preparation (25 degrees C for 1-2 h) with PD(1) (4.5 x 10(-4) - 0.7 x 10(-2) M) followed by centrifugation of the mixture at 53,000 g for 90 min, resulted in loss of the activity both in the supernatant and the sediment, while the protein content in the supernatant and the sediment remained unchanged. After a short incubation (25 degrees for 10 min) with PD(1) (1 x 10(-6) M), followed by centrifugation, the full activity of Na+/K+ -exchanging ATPase in the sediment was restored. These data suggest that peptitergent PD(1) does not solubilize the transmembrane protein Na+/K+ -exchanging ATPase, although it abolishes the cooperative effect of Na+.

A galanin-mastoparan chimeric peptide activates the Na+,K(+)-ATPase and reverses its inhibition by ouabain.

The effect of the neuropeptide galanin, the wasp venom toxin amphiphilic peptide toxin mastoparan and the chimeric peptide, galparan, consisting of N-terminal 13 amino acids of neuropeptide galanin linked at C-terminus to mastoparan amide (and its inactive analog Mas17) on the activity of Na+,K(+)-ATPase has been studied. Mastoparan inhibits the activity of the Na+,K(+)-ATPase with IC50 = 7.5 microM and also reduces the cooperativity for Na+ and K+, respectively, while galanin has no effect on the Na+,K(+)-ATPase activity. The chimeric peptide, galanin(1-13)-mastoparan amide (galparan), exhibits biphasic interaction with Na+,K(+)-ATPase, it activates the enzyme at maximal stimulating concentration of 4 microM followed by inhibition of the enzyme with IC50 of 100 microM. At maximum stimulating concentration (4 microM), galparan partly reduces the cooperativity only for Na+ and it also counteracts the inhibitory effect of oubain on Na+,K(+)-ATPase. Galparan's stimulatory effect was influenced by ATP. The chimeric peptide [19Lys,26Leu]-galparan, containing the inactive analog of mastoparan (Mas17), has no effects on rat brain Na+,K(+)-ATPase activity. Both chimeric peptides galparan and [19Lys,26Leu]-galparan are high-affinity galanin receptor ligands with IC50 of 6.4 nM and 0.71 nM, respectively, while galanin (1-13) and mastoparan alone have significantly lower affinity for the galanin receptor, IC50 of 125 nM and 1 microM, respectively. The ability of chimeric peptides to bind to galanin receptors does not correlate with their effects on the Na+,K(+)-ATPase.

Activation of Na,K-ATPase by an endogenous peptide, PEC-60.

Several peptidic and non-peptidic factors can modulate Na,K-ATPase activity, among them mainly inhibitors of this enzyme, ouabain being the most effective. In a very few cases only, activation of Na,K-ATPase by endogenous factors has been recorded. We have investigated the effect on Na,K-ATPase of a novel regulatory peptide, PEC-60, recently isolated from porcine intestine. Various biological effects have been described for PEC-60 in different tissues, including brain. We have found that PEC-60 caused a dose-dependent activation of Na,K-ATPase from rat brain frontal cortex, whereas the carboxymethylated form of PEC-60 or other hormonal peptides had no effect. The maximal value of activity reaches up to 125% at close to micromolar concentrations of PEC-60 and the dependence can be described with a bell-shaped curve, indicating a complex mechanism for the interaction. The activation of the enzyme by PEC-60 is apparently related to Na(+)-dependent steps of the Na,K-ATPase system. The kinetic parameters for K(+)-phosphatase were unaffected. Moreover, the activating effect was enhanced by preincubation at low concentrations of ATP that transform the enzyme into the Na(+)-form. Due to the crucial physiological role of Na,K-ATPase, its activity has to be finely controlled and thus PEC-60 may be one of the endogenous factors that regulate this enzyme.

Quantitative evaluation of relationship between cardiac energy metabolism and post-ischemic recovery of contractile function.

Quantitative Evaluation of Relationship between Cardiac Energy Metabolism and Post-ischemic Recovery of Contractile Function. Mechanisms of ischemic damage were studied by defining the relationships between post-ischemic work recovery and tissue ATP levels in isolated rat hearts as well as mitochondrial respiration rates in skinned myofibrils. Pre-ischemic levels of ATP were reduced by 2-deoxyglucose treatment and assessed using 31P-NMR. A 70% fall of ATP was not associated with decreased functional recovery. Mitochondrial respiration was assessed without mitochondrial isolation in skinned cardiac fibers in physiological salt solution using a novel method developed by Veksler et al. Maximal rates of mitochondrial respiration were not changed after 35 min of normothermic ischemia using St. Thomas's Hospital cardioplegic solution followed by 30 min of aerobic reperfusion. Only a reversible increase in the rate of basal respiration and a decrease in creatine-stimulated oxygen uptake were observed. Thus, mitochondrial oxidative phosphorylation, as assessed in skinned myofibrils, was tolerant to an ischemic period which induced permanent depression of contractile function along with alterations in metabolite distribution. As a result, tissue level of ATP and rates of mitochondrial respiration provided an estimate of ischemic damage only in cases where damage reached a very severe extent.