Effects of methyl palmoxirate on hypoxic rat atria.

Isolated rat atria in hypoxia released lactate into the bathing medium and underwent a decline of the contraction frequency which, in some cases led to a complete cessation of the pacemaker activity. A pronounced fall in the peak developed tension and a rise in the resting tension also appeared. The atria from 24 h fasted rats, which oxidize faster their reserve lipids than those from fed rats, exhibited greater functional disturbances during hypoxia, a lower lactate output and a smaller recovery of peak tension upon reoxygenation. Methyl palmoxirate, which is a selective inhibitor of carnitine palmitoyltransferase I, attenuated the decline of the beating rate and the rise of the resting tension in both groups of rats and the incidence of atrial arrest in the fasted rat group. The fall in the peak tension, lactate output and recovery upon reoxygenation were not altered by the inhibitor. These data indicate that methyl palmoxirate alleviates some of the hypoxic functional derangements. Hence, it may be inferred that inhibiting the oxidation of the fatty acid derived from the endogenous triacylglycerol is beneficial during oxygen-limited conditions and that these effects could not be ascribed to changes in the glycolytic flux.     

The effects of 4-pentenoic and pentanoic acids on the isolated rat atria

The peak developed tension and the pacemaker frequency of the isolated atria from fed and fasted rats, declined progressively during the incubation in a glucose-free medium containing 2-deoxyglucose. The atria from fed rats exhibited a faster decline than those from fasted rats, which was associated to a slower triacylglycerol lipolysis. 4-Pentenoic acid inhibited the lipolysis of both groups of atria but did not alter the atrial contractile performance. However, it enhanced the decline of the pacemaker frequency in the atria from fasted rats whereas, in contrast, it alleviated the decline in the fed atria. n-Pentanoic acid ameliorated the impairment of the contractile and pacemaker activities in both groups of atria, without affecting the lipolysis. It was concluded that, since the inhibition of the intramyocardial lipolysis did not correlate with changes of the atrial functions, 4-pentenoic acid was not appropriate to assess about the contribution of endogenous triacylglycerol to the maintenance of the atrial contractile and pacemaker activities.     

Effects of methylpalmoxirate on isolated rat atria.

The aim of the investigation was to assess whether endogenous triacylglycerol contributes to the maintenance of the contractile and pacemaker activities of the isolated atria from fed and fasted rats. To attain this information, the atria were treated with methylpalmoxirate which is a potent inhibitor of carnitine palmitoyltransferase I. In the presence of glucose, methylpalmoxirate abolished the lipolysis without affecting peak developed tension or the atrial rate. When exposed to a substrate-free medium containing 2-deoxyglucose, the atria displayed a progressive fall of the pacemaker frequency, a pronounced decay of contractile strength and the appearance of contracture. These derangements appeared faster in the atria from fed rats coinciding with a smaller triacylglycerol mobilization. Methylpalmoxirate suppressed triacylglycerol breakdown, increased the contracture strength, accelerated the fall of the atrial rate and in a significant number of fasted atria it led to a complete cessation of the spontaneous contractions. The decline of the peak tension was not altered by the inhibitor, probably because the contractile strength was too weak in the glucose-free medium, so that additional negative inotropic effects were not detectable. These data suggest that exogenous glucose in addition to that derived from glycogen meet the atrial energy requirements when the fatty acid oxidation is hindered. The deleterious effects exerted by methylpalmoxirate after the glucose metabolism was eliminated indicate that endogenous triacylglycerol supports, at least partly, the atrial functions.     

Effects of hypoxic preconditioning on the hypoxicreoxygenated atria from fed and fasted rats

Hypoxic preconditioning (PC) was studied using rat atria set up isometrically in 10 mM dextrose medium and paced at 1 Hz, applying three different protocols wherein fed and 24-h fasted rats were used in protocols 1 and 2 and only the fed in protocol 3. In protocol 1, PC was achieved applying a 5 min hypoxia followed by 10 min of reoxygenation before the onset of a 60 min hypoxia and 60 min reoxygenation. In protocol 2 the 5 min and a posterior 45 min hypoxia were applied in the absence of dextrose whereas in the 10 min and 60 min reoxygenation periods dextrose was present. In protocol 3, two cycles of 5 min dextrose-free hypoxic periods were applied before the sustained hypoxia (dextrose-free) and reoxygenation periods (10 min and final 45 min, both in the presence of dextrose). In the control groups of all protocols, the equilibration periods were prolonged to compensate the duration of PC. In the control groups of protocols 1 and 2, the sustained hypoxia evoked greater disturbances of contractility and a smaller post-hypoxic recovery in the fasted than in the fed rat atria. In protocol 1, PC markedly reduced the rise in resting tension and improved the post-hypoxic recovery in the fasted rat atria whereas in the fed rat atria protective effects were small and brief. In protocol 2, PC evoked a small reduction of contracture only in the atria from fasted rats and in protocol 3, PC exacerbated the hypoxic disturbances. These data suggest that PC effects depend both on the severity of the PC stress and the sustained hypoxia; and that PC does not require coronary flow.     

Effects of 2-deoxy-D-glucose on the contraction frequency of the isolated atria from fed and fasted rats.

The mere exogenous substrate removal did not change the contraction frequency of the isolated rat atria. However, addition of 2-deoxy-D-glucose together with the glucose removal, elicited a decrease in the atrial frequency. This decrease was significantly greater in the atria from fed rats with respect to those from fasted rats. Near the end of the experiments, only in the atria from fed rats, transient irregular beating appeared. The results suggest that triglycerides constitute the major endogenous substrate of the sinus node pacemaker cells when rats have been previously fasted and that these cells have metabolic features similar to those of contractile fibres.     

Endogenous triacylglycerol utilization by the isolated rat atria

The isolated atria from 24 h fasted rats, either in the presence of glucose or in a substrate-free medium containing 2-deoxyglucose, mobilized the endogenous triacylglycerol (TG) to a greater extent than those from fed rats. The TG of the fasted atria had almost disappeared at the end of the 90 min incubation in the substrate-free plus 2-deoxyglucose medium, whereas in those from fed rats a mobilization-resistant portion of about 40% of the TG pool remained. This finding coincided with a lower decay of the contractile and pacemaker activities in the atria from fasted rats. Insulin abolished the TG mobilization in the atria from fed rats in the presence of glucose, but it was ineffective in the fasted atria. These data suggest that the endogenous-TG and glucose share in supporting the atrial functions, that insulin is involved in the control of TG consumption only in the fed state and that the greater TG mobilization in the fasted atria, at least partly, meets the energy requirements of the tissue.     

Effects of fasting and hypoxic preconditioning on the hypoxic-reoxygenated ventricular strips of the rat heart

The investigation aimed to assess the effects of hypoxic preconditioning in right ventricle strips of fed and 24-h fasted rats, which display a fast fatty acid catabolism, and to ascertain whether these effects are associated with changes in the tissue levels of long-chain acylCoA and acyl carnitine and glycolytic activity. Strips were mounted isometrically in Krebs-bicarbonate solution with 10 mM dextrose and paced at 1 Hz. Strips were exposed to 30 min hypoxia and 60 min reoxygenation with or without a previous preconditioning cycle of 5 min hypoxia followed by a 10 min reoxygenation. During hypoxia the fasted rat strips underwent a greater contracture with respect to the fed group. Preconditioning reduced the contracture strength and accelerated the post-hypoxic recovery only in the fasted rat strips. Hypoxia evoked an increase in the acylCoA and acyl carnitine tissue-contents of the strips which reached higher levels in the fasted than in the fed rat groups. Preconditioning had no effects on the content of these metabolites. During hypoxia lactate output was lower in the fasted than in the fed rat strips and preconditioning abolished this decrease. These data suggest that the protective effects of hypoxic preconditioning occur in the heart tissue predisposed to the oxidation of fatty acid and can not be ascribed to changes in the accumulation of acylCoA and acyl carnitine but could be due, at least in part, to an activation of glycolysis.     

Influence of fasting on the effects of dimethylamiloride and oxfenicine on ischaemic-reperfused rat hearts

To assess whether glycolysis, Na+-H+ exchange and oxidation of fatty acid derived from endogenous lipolysis are involved in the beneficial effects of 24-h fasting on the ischaemic - reperfused heart, it was studied the effects of inhibiting Na+ - H+ exchange using 10 muM dimethylamiloride and fatty acid oxidation using 2 mM oxfenicine, on the functional activity, lactate production and cell viability measured with tetrazolium stain. Since fasting accelerates heart fatty acid oxidation, data were compared to those from fed rats; using Langendorff perfused (glucose 10 mM) hearts of 250-350 g Wistar rats exposed to 25 min ischaemia - 30 min reperfusion. Fasting reduced the ischaemic rise of end diastolic pressure (contracture), improved recovery of contraction and lowered lactate production in comparison with the fed whereas cellular viability was similar in both groups. Dimethylamiloride improved the recovery of contraction (fed control 24 +/- 9%, fed treated 68 +/- 11%, P < 0.05 at the end of reperfusion), attenuated the contracture (fed control 40 +/- 9%, fed treated 24 +/- 11%, P < 0.05 at the beginning of reperfusion) and reduced lactate production in the fed group and increased cellular viability in both groups (fed control 21 +/- 6%, fed treated 69 +/- 7%, P < 0.05, and fasted control 18 +/- 7%, fasted treated 53 +/- 8%, P < 0.05). Oxfenicine reduced the recovery of contraction (fasted control 88 +/- 6%, fasted treated 60 +/- 11%, P < 0.05) and increased lactate production of fasted group and attenuated the contracture in the fed. These data suggest that beneficial effects of fasting owe, at least in part, to a lowered glycolysis probably secondary to the increased fatty acid oxidation and to the accumulation of energy supplying acyl esters. Dimethylamiloride slowing of glycolysis might explain functional improvement, whereas it seems unrelated to the protection on cell viability.     

Stimulation of anaerobic metabolism in rats at high altitude hypoxia--adrenergic effects dependent on dietary states

1. Plasma lactate and pyruvate were increased more markedly in fed rats than in fasted rats exposed to an 8000 m altitude. 2. The increase in plasma lactate and pyruvate was enhanced and inhibited by the alpha 1-adrenergic antagonist prazosin and the beta-blocker propranolol, respectively, in fasted rats exposed to an 8000 m altitude. Blood glucose was not changed by adrenergic blockades under the same conditions. 3. Prazosin and propranolol showed no effect on glycolytic metabolites in plasma in fed rats submitted to an 8000 m altitude. Blood glucose of fed rats was increased by alpha 1-blockade during severe hypoxia. 4. In fasted rats whose energy metabolism depends on oxidation mainly, alpha 1- and beta-adrenergic receptors can participate in the stimulation of respiration and the glycogen degradation, respectively, during an exposure to severe hypoxia. In fed rats energy metabolism depends on glycolysis, which utilizes blood glucose as the substrate preferentially during hypoxia.     

Short-term fasting and lipolytic activity in rat adipocytes.

The aim of this experiment was to study the influence of 18-hour food deprivation on basal and stimulated lipolysis in adipocytes obtained from young male Wistar rats. Fat cells from fed and fasted rats were isolated from the epididymal adipose tissue by collagenase digestion. Adipocytes were incubated in Krebs-Ringer buffer (pH 7.4, 37 degrees C) without agents affecting lipolysis and with different lipolytic stimulators (epinephrine, forskolin, dibutyryl-cAMP, theophylline, DPCPX, amrinone) or inhibitors (PIA, H-89, insulin). After 60 min of incubation, glycerol and, in some cases, also fatty acids released from adipocytes to the incubation medium were determined. Basal lipolysis was substantially potentiated in cells of fasted rats in comparison to adipocytes isolated from fed animals. The inhibition of protein kinase A activity by H-89 partially suppressed lipolysis in both groups of adipocytes, but did not eliminate this difference. The agonist of adenosine A (1) receptor also did not suppress fasting-enhanced basal lipolysis. The epinephrine-induced triglyceride breakdown was also enhanced by fasting. Similarly, the direct activation of adenylyl cyclase by forskolin or protein kinase A by dibutyryl-cAMP resulted in a higher lipolytic response in cells derived from fasted animals. These results indicate that the fasting-induced rise in lipolysis results predominantly from changes in the lipolytic cascade downstream from protein kinase A. The antagonism of the adenosine A (1) receptor and the inhibition of cAMP phosphodiesterase also induced lipolysis, which was potentiated by food deprivation. Moreover, the rise in basal and epinephrine-stimulated lipolysis in adipocytes of fasted rats was shown to be associated with a diminished non-esterified fatty acids/glycerol molar ratio. This effect was presumably due to increased re-esterification of triglyceride-derived fatty acids in cells of fasted rats. Comparing fed and fasted rats for the antilipolytic effect of insulin in adipocytes revealed that short-term food deprivation resulted in a substantial deterioration of the ability of insulin to suppress epinephrine-induced lipolysis.     

Activation of glycogen synthase in myocardium induced by intermittent hypoxia is much lower in fasted than in fed rats

Obstructive sleep apnea is characterized by intermittent obstruction of the upper airway, which leads to intermittent hypoxia. Myocardial glycogen is a major energy resource for heart during hypoxia. Previous studies have demonstrated that intermittent hypoxia rapidly degrades myocardial glycogen and activates glycogen synthase (GS). However, the underlying mechanisms remain undefined. Because sleep apnea/intermittent hypoxia usually happens at night, whether intermittent hypoxia leads to GS activation in the postabsorptive state is not known. In the present study, male adult rats were studied after either an overnight fast or ad libitum feeding with or without intermittent ventilatory arrest (3 90-s periods at 10-min intervals). Hearts were quickly excised and freeze-clamped. Intermittent hypoxia induced a significant decrease in myocardial glycogen content in fed rats and stimulated GS in both fasted and fed rats. However, the portion of GS in the active form increased by approximately 38% in fasted rats compared with a larger, approximately 130% increase in fed rats. The basal G-6-P content was comparable in fasted and fed animals and increased approximately threefold after hypoxia. The basal phosphorylation states of Akt and GSK-3beta and the activity of protein phosphatase 1 (PP1) were comparable between fasted and fed control rats. Hypoxia significantly increased Akt phosphorylation and PP1 activity only in fed rats. In contrast, hypoxia did not induce significant change in GSK-3beta phosphorylation in either fasted or fed rats. We conclude that hypoxia activates GS in fed rat myocardium through a combination of rapid glycogenolysis, elevated local G-6-P content, and increased PP1 activity, and fasting attenuates this action independent of local G-6-P content.     

Hepatic glycogen breakdown is implicated in the maintenance of plasma mannose concentration

D-mannose is an essential monosaccharide constituent of glycoproteins and glycolipids. However, it is unknown how plasma mannose is supplied. The aim of this study was to explore the source of plasma mannose. Oral administration of glucose resulted in a significant decrease of plasma mannose concentration after 20 min in fasted normal rats. However, in fasted type 2 diabetes model rats, plasma mannose concentrations that were higher compared with normal rats did not change after the administration of glucose. When insulin was administered intravenously to fed rats, it took longer for plasma mannose concentrations to decrease significantly in diabetic rats than in normal rats (20 and 5 min, respectively). Intravenous administration of epinephrine to fed normal rats increased the plasma mannose concentration, but this effect was negated by fasting or by administration of a glycogen phosphorylase inhibitor. Epinephrine increased mannose output from the perfused liver of fed rats, but this effect was negated in the presence of a glucose-6-phosphatase inhibitor. Epinephrine also increased the hepatic levels of hexose 6-phosphates, including mannose 6-phosphate. When either lactate alone or lactate plus alanine were administered as gluconeogenic substrates to fasted rats, the concentration of plasma mannose did not increase. When lactate was used to perfuse the liver of fasted rats, a decrease, rather than an increase, in mannose output was observed. These findings indicate that hepatic glycogen is a source of plasma mannose.     

Naloxone's effect on the inotropic and chronotropic responses of isolated, electrically stimulated or spontaneously beating rat atria

Experiments were conducted to determine (i) how naloxone administration alone could modify the inotropic (in electrically stimulated (ES) rat atria) and both the inotropic and chronotropic responses (in spontaneously beating (SB) rat atria) isolated from normotensive and hypotensive (hemorrhaged) rats, and (ii) how naloxone administration would modify the inotropic and chronotropic responses of isolated rat atria previously administered an opiate agonist (morphine), a muscarinic agonist (carbachol), or an alpha- and beta-adrenergic agonist (noradrenaline). Naloxone (51-340 microM) added to ES atria caused a delayed but dose-related decrease in atrial tension (AT), whereas in SB atria, naloxone caused atrial heart rate (AHR) to fall and atrial tension (AT) to increase. Naloxone (68-340 microM), given to SB atria from acutely hypotensive rats, caused a similar increase in atrial tension as seen in the "normotensive" isolated (SB) atria and a similar decrease in atrial heart rate. Morphine sulphate (MS), 37-375 microM, administered to ES atria caused a delayed fall in AT; which was further decreased when naloxone (340 microM) was also added. In the SB atria, morphine caused a dose-related decrease in atrial heart rate whereas atrial tension increased. In SB preparations, atrial heart rate fell even further when naloxone was added to morphine compared with when morphine sulphate was given alone, whereas atrial tension was increased. Noradrenaline (3 or 12 microM) caused a positive, dose-related inotropic response in the ES atria, effects not influenced by the addition of naloxone. In the SB atria, naloxone caused no change in the dose-related increases in atrial tension and heart rate when combined with the lower dose of noradrenaline but decreased AT when combined with 12 microM noradrenaline, compared with when this dose of noradrenaline was given alone. Carbachol (683 nM-1.37 microM) caused a dose-related decrease in atrial tension in ES atria, which was reversed completely by the addition of naloxone. In SB atria, carbachol decreased both atrial tension and heart rate, and with the addition of naloxone (340 microM), a further slight drop in atrial heart rate occurred, but concurrently, a marked rise in atrial tension was observed. The results indicate that naloxone can act with receptors directly within atrial tissue to cause changes in atrial tension and heart rate. The comparable delayed responses of morphine and naloxone suggest their effects are mediated by nonopiate receptors which, in time, cause decreases in calcium influx into the atria.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolic and hormonal response to short term fasting after endurance training in the rat

The metabolic and hormonal response to short term fasting was studied after endurance exercise training. Rats were kept running on a motor driven rodent treadmill 5 days/wk for periods up to 1 h/day for 6 wk. Trained and untrained rats were then fasted for 24 h and 48 h. Liver and muscle glycogen, blood glucose, lactate, beta OH butyrate, glycerol, plasma insulin, testosterone and corticosterone were measured in fed and fasted trained and untrained rats. 48 h fasted trained rats show a lower level of blood lactate (1.08 +/- 0.05 vs 1.33 +/- 0.08 mmol/l-1 of blood glycerol (1 +/- 0.11 vs 0.84 +/- 0.08 mmol/l-1), and of muscle glycogen. There is a significant increase in plasma corticosterone in 48 h fasted trained rats from fed values. Plasma testosterone decreases during fasting, the values are higher in trained rats. Plasma insulin decreases during fasting without any difference between the two groups. These results show higher lipolysis, and decreased glycogenolysis in trained animals during 48 h fasting. The difference between the groups in steroid hormone response could reduce neoglucogenesis and muscle proteolysis in trained animals.     

Effects of pentanoate, 4-pentenoate, 3-hydroxybutyrate and insulin on the tissue-levels of long-chain acyl CoA and acylcarnitine in the oxygenated and hypoxic rat atria.

Under hypoxic conditions the atrial contents of long-chain acyl CoA (LCCoA) and long-chain acylcarnitine display a close correlation with the noxious effects of fasting on the atrial functions as well as with the amelioration effected by inhibitors of carnitine palmitoyltransferase I. These findings suggested that fatty acid oxidation was detrimental for the hypoxic atria. However, since changes of the LCCoA and LCCa levels which may occur together with the hypoxic disturbances attained under some other metabolic interventions had not been assessed yet, present investigation aimed to provide information about this issue. At the end of the prehypoxic equilibration period, all the treatments tested evoked a fall of the free-CoA levels whereas free-carnitine, LCCoA and LCCa remained unchanged. In the hypoxic atria, 4-pentenoate, an inhibitor of fatty acid beta-oxidation that also can be oxidized, did not change LCCoA and LCCa levels whereas the readily oxidizable pentanoate evoked a drop of LCCoA. These effects may be due to the trapping of CoA as the short-chain acyl esters of both substances. Since 4-pentenoate and pentanoate were noxious on the hypoxic atria even though they did not increase LCCoA and LCCa contents, it may be inferred that short-chain acyl esters might be deleterious during oxygen shortage. The exposure to 3-hydroxybutyrate, an oxidizable substrate whose availability increases during fasting, did not alter the LCCoA and LCCa contents, agreeing with the weak detrimental effects that it exerts on the hypoxic atria. On the other hand, insulin elicited a rise in the LCCoA and a fall in the LCCa contents. Inasmuch insulin had been shown to improve the performance of the hypoxic atria, these findings suggest that LCCoA might not be involved in the noxious effects of fatty acid oxidation whereas LCCa would be the major toxic catabolite.     

Age-related changes in rat adipose tissue in response to fasting: protein, lactate and pyruvate levels

1. The evolution with age of the metabolic response of adipose tissue to fasting has been investigated in two groups of rats, at different ages, fed and fasted. 2. The protein tissue content increases in response to fasting in young rats but not in adult-old ones. This indicates a lower lipomobilizing response to starvation with increasing age. 3. In contrast to young rats, the adult rat lactate is not increased by fasting while pyruvate is increased. 4. As a result of lactate and pyruvate variations, NAD/NADH is also changed: after fasting it decreases in young rats, while it increases in older rats. 5. Absolute NAD level is decreased by fasting both in young and older rats. 6. These data provide experimental support for the decreased sensitivity of fat pads from older animals to stimuli affecting lipolysis.     

Nicotinic acid reverses fasting ketosis by lowering the level of cyclic AMP.

When nicotinic acid was administered intraperitoneally to fasted rats, it reversed ketosis, decreased concentrations of cyclic AMP in adipose tissue and liver, and partially suppressed lipolysis. Administration of dibutyryl cyclic AMP reinduced ketosis in fasted rats previously treated with nicotinic acid. The results that nicotinic acid reverses ketosis by lowering tissue levels of cyclic AMP with a consequent suppression of lipolysis and ketogenesis.     

Effects of prostaglandin E1 on lipolysis and plasma free fatty acids in the fasted rat

Contrary to published reports, prostaglandin E(1) (PGE(1)) in vitro and in vivo inhibited fasting lipolysis in rats. Adipose tissue lipolysis was inhibited when the tissue was incubated in the presence of PGE(1) and when the compound was administered intravenously. A biphasic plasma free fatty acid (FFA) response was obtained in fasted rats after intravenous injection of 80 micrograms of PGE(1) per kg body weight; plasma FFA concentrations were lowered at 7 min, elevated at 15 min, and at normal concentrations at 30 min. The FFA depression at 7 min was independent of the animal's nutritional state, but the rebound at 15 min did not occur in fed rats. The plasma FFA rebound in fasted rats at 15 min may be a consequence of rapid inactivation of PGE(1), followed by unopposed activity of factors which enhance fasting lipolysis.     

Effect of dietary fish oil on lung lipid profile and hypoxic pulmonary hypertension

The effects of dietary polyunsaturated fats on chronic hypoxic pulmonary hypertension were assessed in rats fed fish oil, corn oil, or a lower fat, "high-carbohydrate" diet (regular) beginning 1 mo before the start of hypoxia (0.4 atm, n = 30 for each). Mean pulmonary arterial pressures were lower in the chronically hypoxic rats fed fish oil (19.7 +/- 1.8 mm Hg) than in the rats fed corn oil (25.3 +/- 1.6 mm Hg) or regular diets (27.5 +/- 1.5 mm Hg, P less than 0.05). The fish oil diet increased lung eicosapentaenoic acid 50-fold and depleted lung arachidonic acid 60% (P less than 0.0001 for each). Lung thromboxane B2 and 6-ketoprostaglandin F1 alpha levels were lower, and platelet aggregation, in response to collagen, was reduced in rats fed fish oil. Chronically hypoxic rats fed fish oil had lower mortality rates than the other hypoxic rats. They also had lower blood viscosity, as well as less right ventricular hypertrophy and less peripheral extension of vascular smooth muscle to intra-acinar pulmonary arteries (P less than 0.05 for each). The mechanism by which dietary fish oil decreases pulmonary hypertension and vascular remodeling during chronic hypoxia remains uncertain. The finding that a fish oil diet can reduce the hemodynamic and morphological sequelae of chronic hypoxia may have therapeutic significance.     

Effect of dichloroacetate on mechanical performance and metabolism of compromised diaphragm muscle.

We investigated the effect of dichloroacetate (DCA) on tension generation and carbohydrate metabolism of the rat diaphragm in vitro. Isolated diaphragms were placed in individual organ chambers and were hooked to force-displacement transducers. Net lactate production and glucose and lactate oxidation were measured in vitro. Diaphragmatic fatigue was precipitated by in vivo endotoxemic shock, by in vitro hypoxia, or by in vitro repetitive tetanic stimulation. In diaphragms isolated from endotoxemic rats, DCA increased tension generation by 30 and 20% at stimulation frequencies of 20 and 100 Hz, respectively. Associated with changes in mechanical performance, DCA reduced net lactate production by 53% after 60 min of incubation and increased glucose oxidation 54% but had no effect on lactate oxidation. During in vitro hypoxia, DCA reduced net diaphragmatic lactate production by 30% and increased glucose oxidation by 45% but did not attenuate hypoxic fatigue. DCA had no effect on tension generation during repetitive tetanic stimulation. We conclude that DCA improves in vitro diaphragmatic fatigue due to endotoxicosis but not due to hypoxia or repetitive stimulation.