Maternal high fat diet induces early cardiac hypertrophy and alters cardiac metabolism in Sprague Dawley rat offspring.

BACKGROUND AND AIM: Maternal high fat diets (mHFD) have been associated with an increased offspring cardiovascular risk. Recently we found that the class IIa HDAC-MEF2 pathway regulates gene programs controlling fatty acid oxidation in striated muscle. This same pathway controls hypertrophic responses in the heart. We hypothesized that mHFD is associated with activation of signal controlling class II a HDAC activity and activation of genes involved in fatty acid oxidation and cardiac hypertrophy in offspring. METHODS AND RESULTS: Female Sprague Dawley rats were fed either normal fat diet (12%) or high fat diet (43%) three weeks prior to mating, remaining on diets until study completion. Hearts of postnatal day 1 (PN1) and PN10 pups were collected. Bioenergetics and respiration analyses were performed in neonatal ventricular cardiomyocytes (NVCM). In offspring exposed to mHFD, body weight was increased at PN10 accompanied by increased body fat percentage and blood glucose. Heart weight and heart weight to body weight ratio were increased at PN1 and PN10, and were associated with elevated signalling through the AMPK-class IIa HDAC-MEF2 axis. The expression of the MEF2-regulated hypertrophic markers ANP and BNP were increased as were expression of genes involved in fatty acid oxidation. However this was only accompanied by an increased protein expression of fatty acid oxidation enzymes at PN10. NVCM isolated from these pups exhibited increased glycolysis and an impaired substrate flexibility. CONCLUSION: Combined, these results suggest that mHFD induces signalling and transcriptional events indicative of reprogrammed cardiac metabolism and of cardiac hypertrophy in Sprague Dawley rat offspring.

Enhanced glucose uptake via GLUT4 fuels recovery from calcium overload after ischaemia-reperfusion injury in sevoflurane- but not propofol-treated hearts.

BACKGROUND: So far, no study has explored the effects of sevoflurane, propofol, and Intralipid on metabolic flux rates of fatty acid oxidation (FOX) and glucose oxidation (GOX) in hearts exposed to ischaemia-reperfusion. METHODS: Isolated paced working rat hearts were exposed to 20 min of ischaemia and 30 min of reperfusion. Peri-ischaemic sevoflurane (2 vol%) and propofol (100 µM) in the formulation of 1% Diprivan(®) were assessed for their effects on oxidative energy metabolism and intracellular diastolic and systolic Ca(2+) concentrations. Substrate flux was measured using [(3)H]palmitate and [(14)C]glucose and [Ca(2+)] using indo-1AM. Western blotting was used to determine the expression of the sarcolemmal glucose transporter GLUT4 in lipid rafts. Biochemical analyses of nucleotides, ceramides, and 32 acylcarnitines were also performed. RESULTS: Sevoflurane, but not propofol, improved the recovery of left ventricular work (P=0.008) and myocardial efficiency (P=0.008) compared with untreated ischaemic hearts. This functional improvement was accompanied by reduced increases in post-ischaemic diastolic and systolic intracellular Ca(2+) concentrations (P=0.008). Sevoflurane, but not propofol, increased GOX (P=0.009) and decreased FOX (P=0.019) in hearts exposed to ischaemia-reperfusion. GLUT4 expression was markedly increased in lipid rafts of sevoflurane-treated hearts (P=0.016). Increased GOX closely correlated with reduced Ca(2+) overload. Intralipid alone decreased energy charge and increased long-chain and hydroxyacylcarnitine tissue levels, whereas sevoflurane decreased toxic ceramide formation. CONCLUSIONS: Enhanced glucose uptake via GLUT4 fuels recovery from Ca(2+) overload after ischaemia-reperfusion in sevoflurane- but not propofol-treated hearts. The use of a high propofol concentration (100 µM) did not result in similar protection.

AMP-activated protein kinase control of energy metabolism in the ischemic heart.

Myocardial ischemia produces an energy-deficient state in heart muscle, which if not corrected can lead to cardiomyocyte death. AMP-activated protein kinase (AMPK) is a key kinase that can increase energy production in the ischemic heart. During ischemia a rapid activation of AMPK occurs, resulting in an activation of both myocardial glucose uptake and glycolysis, as well as an increase in fatty acid oxidation. This activation of AMPK has the potential to increase energy production, thereby protecting the heart during ischemic stress. However, at clinically relevant high levels of fatty acids, ischemia-induced activation of AMPK also stimulates fatty acid oxidation during and following ischemia. This can contribute to ischemic injury secondary to an inhibition of glucose oxidation, which results in a decrease in cardiac efficiency. As a result, AMPK activation has the potential to be either beneficial or harmful in the ischemic heart.

Glucose plus insulin regulate fat oxidation by controlling the rate of fatty acid entry into the mitochondria.

We tested the hypothesis that glucose plus insulin determine the rate of fat oxidation in humans by controlling the rate of fatty acid entrance into the mitochondria. We gave constant infusions of [1-13C]oleate, a long-chain fatty acid, and [1-14C]octanoate, a medium-chain fatty acid, for 3 h in seven volunteers (basal). Immediately after the basal period, a hyperinsulinemic (insulin infusion = 120 mU x m(-2) min(-1)), hyperglycemic (plasma glucose = 140 mg/dl) clamp was started and continued for 5 h. During the last 3 h of the clamp, the infusions of [1-13C]oleate and [1-14C]octanoate were repeated. Intracellular acylcarnitine concentrations were measured in muscle biopsies obtained before and after the clamp. Plasma oleate enrichment and FFA concentration were kept constant by means of variable infusions of lipids and heparin. Oleate, but not octanoate, requires carnitine binding to gain access to the mitochondrial matrix; hence, if glucose and/or insulin limit long-chain fatty acid entrance into the mitochondria, then, during the clamp, long-chain acylcarnitine formation should be decreased, causing a decrease in oleate, but not octanoate, oxidation. Oleate oxidation decreased from the basal value of 0.7+/-0.1 to 0.4+/-0.1 micromol x kg(-1) x min(-1) (P < 0.05). In contrast, octanoate oxidation remained unchanged. Long-chain acylcarnitine concentration decreased from 855+/-271 in the basal state to 376+/-83 nmol/gram dry weight during the clamp (P < 0.05). We conclude that glucose and/or insulin determine fatty acid oxidation by controlling the rate of long-chain fatty acid entrance into the mitochondria.

Mechanisms responsible for enhanced fatty acid utilization by perfused hearts from type 2 diabetic db/db mice.

The aim of this study was to determine the biochemical mechanism(s) responsible for enhanced FA utilization (oxidation and esterification) by perfused hearts from type 2 diabetic db/db mice. The plasma membrane content of fatty acid transporters FAT/CD36 and FABPpm was elevated in db/db hearts. Mitochondrial mechanisms that could contribute to elevated rates of FA oxidation were also examined. Carnitine palmitoyl transferase-1 activity was unchanged in mitochondria from db/db hearts, and sensitivity to inhibition by malonyl-CoA was unchanged. Malonyl-CoA content was elevated and AMP kinase activity was decreased in db/db hearts, opposite to what would be expected in hearts exhibiting elevated rates of FA oxidation. Uncoupling protein-3 expression was unchanged in mitochondria from db/db hearts. Therefore, enhanced FA utilization in db/db hearts is most likely due to increased FA uptake caused by increased plasma membrane content of FA transporters; the mitochondrial mechanisms examined do not contribute to elevated FA oxidation observed in db/db hearts.

Glycolysis and glucose oxidation during reperfusion of ischemic hearts from diabetic rats.

Stimulation of glucose oxidation by dichloroacetate (DCA) treatment is beneficial during recovery of ischemic hearts from non-diabetic rats. We therefore determined whether DCA treatment of diabetic rat hearts (in which glucose use is extremely low), increases recovery of function of hearts reperfused following ischemia. Isolated working hearts from 6 week streptozotocin-diabetic rats were perfused with 11 mM [2-3H/U-14C]glucose, 1.2 mM palmitate, 20 microU/ml insulin, and subjected to 30 min of no flow ischemia followed by 60 min reperfusion. Heart function (expressed as the product of heart rate and peak systolic pressure), prior to ischemia, was depressed in diabetic hearts compared to controls (HR x PSP x 10(-3) was 18.2 +/- 1 and 24.3 +/- 1 beats/mm Hg/min in diabetic and control hearts respectively) but recovered to pre-ischemic levels following ischemia, whereas recovery of control hearts was significantly decreased (17.8 +/- 1 and 11.9 +/- 3 beats/mm Hg/min in diabetic and control hearts respectively). This enhanced recovery of diabetic rat hearts occurred even though glucose oxidation during reperfusion was significantly reduced as compared to controls (39 +/- 6 and 208 +/- 42 nmol/min/g dry wt, in diabetic and control hearts respectively). Glycolytic rates (3H2O production) during reperfusion were similar in diabetic and control hearts (1623 +/- 359 and 2071 +/- 288 nmol/min/g dry wt, respectively). If DCA (1 mM) was added at reperfusion, hearts from control animals exhibited a significant improvement in function (HR x PSP x 10(-3) recovered to 20 +/- 4 beats/mm Hg/min) that was accompanied by a 4-fold increase in glucose oxidation (from 208 +/- 42 to 753 +/- 111 nmol/min/g dry wt). DCA was without effect on functional recovery of diabetic rat hearts during reperfusion but did significantly increase glucose oxidation from 39 +/- 6 to 179 +/- 44 nmol/min/g dry wt). These data suggest that, unlike control hearts, low glucose oxidation rates are not an important factor in reperfusion recovery of previously ischemic diabetic rat hearts.

The fate of arachidonic acid and linoleic acid in isolated working rat hearts containing normal or elevated levels of coenzyme A.

If myocardial levels of coenzyme A (CoA) are elevated, an increase in the rate of esterification of palmitate into myocardial triacylglycerols will occur. In this study, we determined the fate of linoleic acid and arachidonic acid in isolated working rat hearts containing normal or elevated levels of CoA. In hearts containing normal levels of CoA, oxidative rates (measured as 14CO2 production) of [14C]arachidonic acid were significantly lower than those of [14C]palmitic acid, whereas a significantly greater incorporation of [14C]arachidonic acid into myocardial neutral lipids (comprised predominantly of triacylglycerols) was seen when compared to hearts perfused with [14C]palmitic acid. In a second series of hearts, myocardial CoA levels were elevated by perfusing hearts with no carbon substrate, 15 microM pantothenate, 0.5 mM cysteine and 1 mM dithiothreitol, resulting in an increase in myocardial CoA levels from 553 +/- 2 to 918 +/- 63 nmol/g dry wt. Subsequent perfusion of hearts containing elevated CoA levels with 1.2 mM [3H]arachidonic acid or [14C]linoleic acid resulted in a significant increase in incorporation of both these fatty acids into myocardial neutral lipids compared to control hearts. Incorporation of these fatty acids into phospholipids was significantly lower than their incorporation into neutral lipids and was not affected by myocardial CoA levels. Linoleic acid oxidation was unaffected by increases in myocardial levels of CoA. If linoleic acid oxidation was inhibited by adding 5 mM pyruvate to the perfusate, no effect on the incorporation of [14C]linoleic acid into neutral lipids was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose oxidation rates in fatty acid-perfused isolated working hearts from diabetic rats.

The effect of fatty acids and the carnitine palmitoyltransferase I (CPT I) inhibitor, Etomoxir, on myocardial glucose oxidation in diabetes was studied. 14CO2 production from 11 mM [14C]glucose was measured in control or 6-week streptozotocin-diabetic isolated working rat hearts perfused with or without 1.2 mM palmitate (bound to 3% albumin). In control hearts, addition of palmitate to the buffer resulted in a marked reduction (13-fold) in glucose oxidation rates. Glucose oxidation in diabetic rat hearts perfused with palmitate was almost abolished. Even though glucose oxidation rates were low, exogenous palmitate oxidation rates, measured as 14CO2 production from [14C]palmitate, were not increased in diabetic versus control hearts. Addition of the CPT 1 inhibitor, Etomoxir (1.10(-6) M), resulted in a doubling of glucose oxidation rates in both control and diabetic rat hearts, in the presence or absence of palmitate. The effects of Etomoxir on glucose oxidation could not be explained by reduced exogenous palmitate oxidation or decreased levels of citrate. Cardiac function, as measured by the heart rate x peak systolic pressure product, was reduced in diabetic rat hearts. Etomoxir significantly increased heart function in palmitate-perfused hearts from both control and diabetic rats. These data suggest that fatty acids contribute to decreased glucose oxidation and cardiac function in diabetic rat hearts. These effects of fatty acids can be partially reversed with the CPT 1 inhibitor, Etomoxir.

[3H]iloprost and prostaglandin E2 compete for the same receptor site on cardiac sarcolemmal membranes.

We have previously demonstrated that high-affinity PGE receptors are present on purified cardiac sarcolemmal (SL) membrane from bovine heart (Lopaschuk et al. (1989) Circ. Res. 65, 538-545). In this study we determined whether PGI2 receptors are also present on the cardiac SL membrane. Due to the extreme lability of prostacyclin (PGI2) under physiological conditions, the PGI2 analogue, Iloprost was substituted for PGI2. 3H-Iloprost specifically bound to two sites on the SL membrane; one of high affinity (Kd = 0.3 nM, Bmax = 97.0 fmol/mg SL), and one of lower affinity (Kd = 20.6 nM, Bmax = 1589 fmol/mg SL). Competition studies demonstrated that the concentrations of PGE2 and PGE1 necessary to displace 50% of the specific binding of 20 nM [3H]Iloprost on cardiac SL were 15-fold lower than the concentrations of unlabelled Iloprost necessary to displace 50% of binding. In contrast, a 15-fold higher concentration of unlabelled Iloprost was needed to displaced 50% of specific binding of 2 nM [3H]PGE2 compared to the concentrations of PGE1 or PGE2 required to displace 50% of [3H]PGE2 binding. In summary, our results indicate that a prostacyclin receptor is present on the cardiac sarcolemmal membrane, and that PGI2 competes for the same receptor site as PGE2.

Acetyl-CoA carboxylase control of fatty acid oxidation in hearts from hibernating Richardson's ground squirrels.

Although mammalian hibernators rely on stored body fat as a source of energy, direct measurement of energy substrate preference in heart tissue during hibernation, as well as potential mechanisms controlling fatty acid oxidation has not been examined. In order to determine whether an increase in fatty acid utilization occurs during hibernation, glucose and palmitate oxidation were measured in isolated working hearts from hibernating and non-hibernating Richardson's ground Squirrels. Hearts were perfused at either 37 degrees or 5 degrees C with perfusate containing 11 mM [U-14C]glucose and 1.2 mM [9,10-3H]palmitate, which allowed for direct measurement of both glucose oxidation (14CO2 production) and fatty acid oxidation (3H2O production). The contribution of fatty acid oxidation as a source of citric acid cycle acetyl-CoA was significantly greater in hearts from hibernating animals, compared to hearts from non-hibernating animals. Since acetyl-CoA carboxylase (ACC) regulates cardiac fatty acid oxidation (producing malonyl-CoA, a potent inhibitor of mitochondrial fatty acid uptake), we measured the activity and expression of ACC in these hearts. ACC activity was significantly decreased in hibernating ground squirrels, regardless of whether ACC was assayed at 37 degrees or 5 degrees C. This decrease in activity could not be explained by a change in the activity of 5'AMP-activated protein kinase, which can phosphorylate and inhibit ACC. Rather, the expression of the 280 kDa isoform of ACC (which predominates in cardiac muscle) was decreased in hearts from hibernating squirrel hearts. This suggests that a down regulation of ACC expression occurs as an adaptation for the increased utilization of fatty acid in hearts of hibernating ground squirrels.

Characterization of 5'AMP-activated protein kinase activity in the heart and its role in inhibiting acetyl-CoA carboxylase during reperfusion following ischemia.

Despite the high expression of 5'AMP activated protein kinase (AMPK) in heart, the activity and function of this enzyme in heart muscle has not been characterized. We demonstrate that rat hearts have a high AMPK activity, comparable to that found in liver, which could be stimulated up to 3-fold by 5'AMP. Cardiac AMPK is also under phosphorylation control, since in vitro incubation of cardiac AMPK with protein phosphatase 2A completely abolished activity, while incubation with ATP/Mg(2+) resulted in over a 2-fold increase in activity. To investigate the function of AMPK in heart muscle, isolated working rat hearts were subjected to 30 min of global no-flow ischemia, followed by 60 min of aerobic reperfusion. AMPK activity was increased in heart at the end of reperfusion compared to aerobic controls (379 +/- 53 (n=5) vs. 139 +/- 19 (n=5) pmol x min(-1) x mg protein(-1), P<0.05, respectively). Treatment of AMPK in vitro with protein phosphatase 2A reversed this activation. Since AMPK can phosphorylate and inactivate acetyl-CoA carboxylase (ACC) in other tissues, and heart ACC has an important role in regulating fatty acid oxidation, we measured ACC activity in hearts reperfused post-ischemia. ACC activity was decreased at the end of reperfusion compared to aerobic controls (3.64 +/- 0.36 (n=9) vs. 10.93 +/- 0.60 (n=11) nmol x min(-1) x mg protein(-1), respectively, P<0.05). A significant negative correlation (r= -0.78) was observed between AMPK activity and ACC activity measured in aerobic and reperfused ischemic hearts. Low ACC activity could be reversed if ACC was extracted from hearts in the absence of phosphatase inhibitors, suggesting that phosphorylation of ACC decreased enzyme activity. This suggests that following ischemia AMPK is phosphorylated and activated (possibly by an AMPK kinase). AMPK then phosphorylates and inactivates ACC. The resultant decrease in malonyl-CoA levels could explain the acceleration of fatty acid oxidation that is observed during reperfusion of ischemic hearts.

Insulin effects on pantothenic acid uptake in isolated perfused working hearts from diabetic rats.

Pantothenic acid uptake was studied in isolated working hearts from spontaneously diabetic BB Wistar and streptozocin-induced diabetic (STZ-D) rats. If insulin treatment was stopped for a 24-h period from spontaneously diabetic rats, a significant decrease in the rate of pantothenic uptake was noted (from 147.3 +/- 5.0 to 110.8 +/- 10.6 nmol.g-1 dry wt.30 min-1). Pantothenic acid uptake rates were also reduced in 48-h STZ-D rats (118.0 +/- 6.1 nmol.g-1 dry wt.30 min-1, compared to 158.2 +/- 5.3 in control rats). The decrease in pantothenic acid uptake in all diabetic animals occurred whether hearts were perfused with 1.2 mM palmitate or 1.2 mM palmitate and 11 mM glucose. If insulin (500 microU/ml) was added to the perfusion medium of hearts from spontaneously diabetic rats perfused with palmitate and glucose, a significant increase in pantothenic acid uptake was noted (from 110.8 +/- 10.6 to 167.0 +/- 9.4 nmol.g-1 dry wt.30 min-1). Insulin had no significant effect on pantothenic acid uptake in hearts from spontaneously diabetic rats perfused with palmitate alone. In STZ-D rats, insulin added to hearts perfused with palmitate and glucose resulted in a small but significant increase in pantothenic acid uptake (from 118.0 +/- 6.1 to 130.6 +/- 4.0 nmol.g-1 dry wt.30 min-1). Insulin had no effect on pantothenic acid uptake in control hearts perfused either in the presence or absence of glucose. These data suggest that insulin, in the presence of glucose, can increase pantothenic acid uptake in diabetic rats.

Volume overload hypertrophy of the newborn heart slows the maturation of enzymes involved in the regulation of fatty acid metabolism.

OBJECTIVES: The purpose of this study was to determine the effect of volume overload hypertrophy in the newborn heart on the cardiac enzymes controlling fatty acid metabolism. BACKGROUND: Shortly after birth, a rise in 5'-adenosine monophosphate-activated protein kinase (AMPK) activity results in the phosphorylation and inhibition of acetyl coenzyme A (CoA) carboxylase (ACC), and a decline in myocardial malonyl CoA levels with increased fatty acid oxidation rates. Whether the early onset of hypertrophy in the newborn heart alters this maturational increase in fatty acid oxidation is unknown. METHODS: Newborn piglets underwent endovascular stenting of the ductus arteriosus on day 1 of life with a 4.5-mm diameter stent, resulting in a left to right shunt, and left ventricular (LV) volume loading. Left ventricular and right ventricular samples from fetal, newborn, three-week control and three-week stented animals were compared. RESULTS: Stenting resulted in echocardiographic evidence of volume overload and myocardial hypertrophy. In control animals, left ventricular ACC activity declined from 274 +/- 30 pmol/mg/min on day 1 to 115 +/- 12 after three weeks (p < 0.05), but did not display this maturation drop in hypertrophied hearts, remaining elevated (270 +/- 50 pmol/mg/min, p < 0.05). At three weeks, malonyl CoA levels remained 2.8-fold higher in hypertrophied hearts than in control hearts. In control hearts, LV AMPK activity increased 178% between day 1 and three weeks, whereas in hypertrophied hearts AMPK activity at three weeks was only 71% of control values, due to a significant decrease in expression of the catalytic subunit of AMPK. CONCLUSIONS: Early onset LV volume overload with hypertrophy results in a delay in the normal maturation of fatty acid oxidation in the newborn heart.

Dichloroacetate improves postischemic function of hypertrophied rat hearts.

OBJECTIVES: We sought to determine whether improving coupling between glucose oxidation and glycolysis by stimulating glucose oxidation during reperfusion enhances postischemic recovery of hypertrophied hearts. BACKGROUND: Low rates of glucose oxidation and high glycolytic rates are associated with greater postischemic dysfunction of hypertrophied as compared with nonhypertrophied hearts. METHODS: Heart function, glycolysis and glucose oxidation were measured in isolated working control and hypertrophied rat hearts for 30 min before 20 min of global, no-flow ischemia and during 60 min of reperfusion. Selected control and hypertrophied hearts received 1.0 mmol/liter dichloroacetate (DCA), an activator of pyruvate dehydrogenase, at the time of reperfusion to stimulate glucose oxidation. RESULTS: In the absence of DCA, glycolysis was higher and glucose oxidation and recovery of function were lower in hypertrophied hearts than in control hearts during reperfusion. Dichloroacetate stimulated glucose oxidation during reperfusion approximately twofold in both groups, while significantly reducing glycolysis in hypertrophied hearts. It also improved function of both hypertrophied and control hearts. In the presence of DCA, recovery of function of hypertrophied hearts was comparable to or better than that of untreated control hearts. CONCLUSIONS: Dichloroacetate, given at the time of reperfusion, normalizes postischemic function of hypertrophied rat hearts and improves coupling between glucose oxidation and glycolysis by increasing glucose oxidation and decreasing glycolysis. These findings support the hypothesis that low glucose oxidation rates and high glycolytic rates contribute to the exaggerated postischemic dysfunction of hypertrophied hearts.

Controversies on the sensitivity of the diabetic heart to ischemic injury: the sensitivity of the diabetic heart to ischemic injury is decreased.

Controversy exists as to whether the diabetic heart is more or less sensitive to ischemic injury. Although a considerable number of experimental studies have directly determined the effects of ischemia on the diabetic heart, there is still no general agreement as to whether metabolic changes within the myocardium contribute to the severity of ischemic injury. This paper reviews the evidence suggesting that the diabetic heart can actually be less sensitive to an episode of severe ischemia. Possible reasons for this decreased sensitivity to injury are discussed, which include a decreased accumulation of glycolytic products during ischemia (lactate and protons), as well as alterations in the regulation of intracellular pH in the diabetic heart. Based on existing studies, we suggest that although impaired glucose metabolism in the diabetic heart contributes to injury in hypoxic hearts or in hearts subjected to low-flow ischemia, diabetes-induced decreases in glycolysis can actually be beneficial to the diabetic heart during and following a severe ischemic episode. A decreased clearance of protons via the Na+/H+ exchanger may also contribute to the decreased sensitivity to ischemic injury in the diabetic heart.

Regulation of energy substrate metabolism in the diabetic heart.

The effects of diabetes on myocardial metabolism are complex in that they are tied to the systemic metabolic abnormalities of the disease (hyperglycemia and elevated levels of free fatty acid and ketone bodies), and changes in cardiomyocyte phenotype (e.g., down-regulation of glucose transporters and PDH activity). The cardiac adaptations appear to be driven by the severity of the systemic abnormalities of the disease. The diabetes-induced changes in the plasma milieu and cardiac phenotype both cause impaired glycolysis, pyruvate oxidation, and lactate uptake, and a greater dependency on fatty acids as a source of acetyl CoA. Studies in isolated hearts suggest that therapies aimed at decreasing fatty acid oxidation, or directly stimulating pyruvate oxidation would be of benefit to the diabetic heart during and following myocardial ischemia.

L-carnitine increases glucose metabolism and mechanical function following ischaemia in diabetic rat heart.

OBJECTIVE: Stimulation of glucose oxidation by L-carnitine improves mechanical recovery of ischaemic hearts from non-diabetic rats perfused with high levels of fatty acids. The aim of this study was to determine whether L-carnitine also increases glucose oxidation and function in diabetic rat hearts, which have suppressed glucose metabolism. METHODS: Isolated working hearts from six week streptozotocin diabetic and control rats were perfused with 11 mM (5-3H/U-14C)-glucose, 1.2 mM palmitate. Hearts were paced at 260 beats.min-1 during 60 min of low flow ischaemia, and were then subjected to 30 min of aerobic reperfusion. Total myocardial carnitine content in these hearts was first increased by a 60 min aerobic perfusion with 10 mM L-carnitine. RESULTS: Steady state glucose oxidation rates (measured as 14CO2 production) were depressed in diabetic rat hearts compared to control hearts during the initial aerobic period. However, L-carnitine treatment dramatically increased glucose oxidation rates in the diabetic rat hearts, as well as in control hearts. Glycolysis was also lower in diabetic rat hearts compared to control hearts, although L-carnitine treatment significantly increased glycolysis only in the diabetic animals. During reperfusion, steady state rates of glucose oxidation and glycolysis returned to preischaemic values in both the control and diabetic groups. L-carnitine treatment stimulated glucose oxidation during reperfusion in control and diabetic rat hearts. Mechanical function of control hearts returned to 38(SEM 9)% of preischaemic values, whereas in L-carnitine treated hearts function returned to 90(7)% of preischaemic values. Recovery of function was 80(15)% of preischaemic in the diabetic rat hearts, and was increased to 100% of preischaemic function with L-carnitine. CONCLUSIONS: Carnitine improves recovery of function of ischaemic non-diabetic rats by stimulating glucose oxidation during reperfusion, whereas it may be beneficial in diabetic rat hearts by stimulating both glycolysis during ischaemia and glucose oxidation during reperfusion.

Developmental changes in energy substrate use by the heart.

Marked changes in intermediary metabolism occur during development of the heart. In the fetus, the heart utilises lactate and glucose as its main energy substrates, while in the adult, fatty acids are the main energy substrate. The transition from carbohydrate to fatty acid metabolism is a complex process which involves maturation of mitochondrial processes and dramatic changes in circulating levels of fatty acids and lactate. In addition, developmental changes in the use of energy substrates also involve changes in the regulation of the enzymes involved in both carbohydrate and fatty acid utilisation. This paper reviews these changes in intermediary metabolism which occur during myocardial development. The metabolic differences that exist between immature and adult hearts may explain the observed differences in the ability of immature hearts to withstand hypoxaemia or ischaemia.

Regulation of myocardial carbohydrate metabolism under normal and ischaemic conditions. Potential for pharmacological interventions.

It is now clear that the availability of different metabolic substrates can have a profound influence on the extent of damage incurred during episodes of cardiac ischaemia, and on cardiac functional recovery on reperfusion following ischaemia. In particular, increases in fatty acid availability and oxidation, compared to glucose oxidation, under such conditions leads to a worsening of outcome. Therefore metabolic interventions aimed at enhancing glucose utilisation and pyruvate oxidation at the expense of fatty acid oxidation is a valid therapeutic approach to the treatment of myocardial ischaemia. In particular, the development of agents which will promote full glucose oxidation as opposed to glycolysis alone, offer clear advantages. This can be accomplished by different means, including direct or indirect inhibition of CPT-I or inhibition of fatty acid beta-oxidation, or by direct or indirect activation of PDH. It is not yet clear which of these approaches offers the best treatment of cardiac ischaemia. To date, trimetazidine and carnitine have received limited approval in Europe for the treatment of angina; large scale clinical trials with the other agents mentioned above have not been completed. The increasing availability of agents affecting these specific sites, and the increasingly sophisticated techniques for assessing myocardial metabolism, should allow elucidation of the optimum metabolic targets and development of novel pharmacological agents for the treatment of ischaemic heart disease.

Increased cardiac fatty acid uptake with dobutamine infusion in swine is accompanied by a decrease in malonyl CoA levels.

OBJECTIVE: Malonyl CoA is an important regulator of fatty acid oxidation in the heart secondary to its ability to inhibit carnitine palmitoyltransferase 1 (CPT 1). Malonyl CoA is produced from acetyl CoA in a reaction catalyzed by acetyl CoA carboxylase (ACC). In this study we determined if alterations in malonyl CoA regulation of fatty acid metabolism are involved in the increase in energy transduction seen following an increase in cardiac work. METHODS: Anesthetized, open-chest, domestic swine were subjected to a 30 min control period followed by a 30 min treatment period with either dobutamine (15 micrograms.kg-1. min-1 i.v.) (n = 6) or saline (n = 6). RESULTS: Heart rate, left ventricular peak dp/dt, and MVO2, were significantly increased in the dobutamine group compared to the saline group during the treatment period. Free fatty acid and glucose uptake were increased 210 and 248%, respectively, in the dobutamine group during the treatment period. Malonyl CoA content was decreased by 55% (from 0.40 +/- 0.05 to 0.18 +/- 0.12 nmol/g wet wt; P < 0.05) with dobutamine treatment, but was not affected by saline treatment. ACC activity was not significantly different between groups (0.31 +/- 0.02 vs. 0.30 +/- 0.04 nmol. min-1. mg protein-1, respectively). The activity of AMP-dependent protein kinase (AMPK), which phosphorylates and inactivates ACC, was also not significantly different in the dobutamine hearts compared to the saline hearts (322 +/- 26 vs. 338 +/- 39 pmol. min-1. mg protein-1, respectively). CONCLUSION: The increased cardiac work following dobutamine infusion is accompanied by a decrease in malonyl CoA levels and an increase in fatty acid uptake. However, the decrease in malonyl CoA cannot be explained by a decrease in ACC activity.