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PubMed1967

Metabolic activities of the isolated perfused rat kidney.

1. A technique for perfusing the isolated rat kidney is described. It is primarily designed for the study of renal metabolism but is also suitable for studying some aspects of the secretory function; this was normal with respect to minimal glucosuria. The glomerular filtration rate as measured by creatinine clearance was lower than in vivo and slowly decreased with time. 2. Gluconeogenesis from a variety of precursors was rapid and similar to that in kidney-cortex slices, in contrast with liver where the perfused organ is more effective than slices. Whereas the maximal rates of gluconeogenesis from glycerol and pyruvate were similar in liver and kidney, the rates from succinate, malate and fumarate were 14-20 times, and those from glutamate and aspartate about three times, as high in the kidney. 3. The oxygen consumption of the perfused organ was about twice that of cortex slices, presumably because of the secretory work done in the perfused organ but not in slices. 4. The rate of acetoacetate oxidation was about the same in the perfused organ and in slices but, because of the higher rate of oxygen consumption, the percentage contribution of acetoacetate to the fuel of respiration was lower in the perfused organ. The results suggest that acetoacetate can supply energy for the basal requirements and for gluconeogenesis but not for the secretory work. 5. Glutamine was formed at a high rate from glutamate and at a lower rate from aspartate. The high rates indicate that, in the rat, the kidney is a major source of body glutamine.

Acetoacetates↗
PubMed1969

The fuel of respiration of rat kidney cortex.

1. In kidney-cortex slices from the well-fed rat, glucose (5mm) supplied 25-30% of the respiratory fuel; in the starved state, the corresponding value was 10%. These results are based on measurements of the net uptake of glucose and of the specific radioactivity of labelled carbon dioxide formed in the presence of [U-(14)C]-glucose. 2. Added acetoacetate (5mm) or butyrate (10mm) provided up to 80%, and added oleate (2mm) up to 50% of the fuel of respiration. The oxidation of endogenous substrates was suppressed correspondingly. 3. More [U-(14)C]oleate was removed by the tissue than could be oxidized by the amount of oxygen taken up; less than 25% of the oleate removed was converted into respiratory carbon dioxide and about two-thirds was incorporated into the tissue lipids. The rate of oleate incorporation into the neutral-lipid fraction was calculated to be equivalent to the rate of oxidation of endogenous fat, which provided the chief remaining fuel. 4. The contribution of endogenous substrates to the respiration (50%) in the presence of added oleate is taken to reflect either a high turnover rate of the endogenous neutral lipids (approx. half-life 2.5hr.) or a raised rate of lipolysis caused by the experimental conditions in vitro. 5. Added l-alpha-glycerophosphate (2.5mm) increased oleate incorporation into the neutral-lipid fraction by up to 40% (i.e. caused a net synthesis of triglyceride). 6. Lactate (2.5mm) added as sole substrate supplied 30% of the respiratory fuel, but with added oleate (2mm) lactate was converted quantitatively into glucose. Oleate stimulated the rate of gluconeogenesis from lactate by 45%. 7. The oxidation of both long-chain and short-chain even-numbered fatty acids was accompanied by ketone-body formation. Ketone-body synthesis from oleate, but not from butyrate, increased six- to seven-fold after 48hr. of starvation. The maximum rates of renal ketogenesis (80mumoles/hr./g. dry wt., with butyrate) were about 20% of the maximum rates observed in the liver (on a weight-for-weight basis) and accounted for, at most, 35% of the fatty acid removed. 8. dl-Carnitine (1.0mm) had no effect on the rates of uptake of acetate, butyrate or oleate or on the rate of radioactive carbon dioxide formation from [U-(14)C]oleate, but increased ketone-body formation from oleate by more than 100%. Ketone-body formation from butyrate was not increased. 9. There is evidence supporting the assumption that there are cells in which gluconeogenesis and ketogenesis occur together, characterized by equal labelling of [U-(14)C]oleate and the ketone bodies formed, and other cells that oxidize fat and do not form ketone bodies. 10. Inhibitory effects of unlabelled acetoacetate on the oxidation of [1-(14)C]butyrate and of unlabelled butyrate on [4-(14)C]acetoacetate oxidation show that fatty acids and ketone bodies compete as fuels on the basis of their relative concentrations. 11. The pathway of ketogenesis in renal cortex must differ from that of the liver, as beta-hydroxy-beta-methylglutaryl-CoA synthetase is virtually absent from the kidney. In contrast with the liver the kidney possesses 3-oxo acid CoA-transferase (EC 2.8.3.5), and the ready reversibility of this reaction and that of thiolase (EC 2.3.1.9) provide a mechanism for ketone-body formation from acetyl-CoA. This mechanism may apply to extrahepatic tissues generally, with the possible exception of the epithelium of the rumen and intestines.

Acetoacetates↗
PubMed1970

Effects of ischaemia on metabolite concentrations in rat liver.

1. Changes in the concentrations of ammonia, glutamine, glutamate, 2-oxoglutarate, 3-hydroxybutyrate, acetoacetate, alanine, aspartate, malate, lactate, pyruvate, NAD(+), NADH and adenine nucleotides were measured in freeze-clamped rat liver during ischaemia. 2. Although the concentrations of most of the metabolites changed rapidly during ischaemia the ratios [glutamate]/[2-oxoglutarate][NH(4) (+)] and [3-hydroxybutyrate]/[acetoacetate] changed equally and the value of the expression [3-hydroxybutyrate][2-oxoglutarate][NH(4) (+)]/[acetoacetate][glutamate] remained approximately constant, indicating that the 3-hydroxybutyrate dehydrogenase and glutamate dehydrogenase systems were at near-equilibrium with the mitochondrial NAD(+) couple. 3. The value of the expression [alanine][oxoglutarate]/[pyruvate][glutamate] was about 0.7 in vivo and remained fairly constant during the ischaemic period of 5min, although the concentrations of alanine and oxoglutarate changed substantially. No explanation can be offered why the value of the ratio differed from that of the equilibrium constant of the alanine aminotransferase reaction, which is 1.48. 4. Injection of l-cycloserine 60min before the rats were killed increased the concentration of alanine in the liver fourfold and decreased the concentration of the other metabolites measured, except that of pyruvate. During ischaemia the concentration of alanine did not change but that of aspartate almost doubled. 5. After treatment with l-cycloserine the value in vivo of the expression [alanine][oxoglutarate]/[pyruvate][glutamate] rose from 0.7 to 2.4. During ischaemia the value returned to 0.8. 6. The effects of l-cycloserine are consistent with the assumption that it specifically inhibits alanine aminotransferase. 7. Most of the alanine formed during ischaemia is probably derived from pyruvate and from ammonia released by the deamination of adenine nucleotides and glutamine. The alanine is presumably formed by the combined action of glutamate dehydrogenase and alanine aminotransferase. 8. The rate of anaerobic glycolysis, calculated from the increase in the lactate concentration, was 1.3mumol/min per g fresh wt. 9. Although the concentrations of the adenine nucleotides changed rapidly during ischaemia, the ratio [ATP][AMP]/[ADP](2) remained constant at 0.54, indicating that adenylate kinase established near-equilibrium under these conditions.

Acetoacetates↗
PubMed1970

Ketone body and fatty acid metabolism in sheep tissues. 3-Hydroxybutyrate dehydrogenase, a cytoplasmic enzyme in sheep liver and kidney.

1. 3-Hydroxybutyrate dehydrogenase (EC 1.1.1.30) activities in sheep kidney cortex, rumen epithelium, skeletal muscle, brain, heart and liver were 177, 41, 38, 33, 27 and 17mumol/h per g of tissue respectively, and in rat liver and kidney cortex the values were 1150 and 170 respectively. 2. In sheep liver and kidney cortex the 3-hydroxybutyrate dehydrogenase was located predominantly in the cytosol fractions. In contrast, the enzyme was found in the mitochondria in rat liver and kidney cortex. 3. Laurate, myristate, palmitate and stearate were not oxidized by sheep liver mitochondria, whereas the l-carnitine esters were oxidized at appreciable rates. The free acids were readily oxidized by rat liver mitochondria. 4. During oxidation of palmitoyl-l-carnitine by sheep liver mitochondria, acetoacetate production accounted for 63% of the oxygen uptake. No 3-hydroxybutyrate was formed, even after 10min anaerobic incubation, except when sheep liver cytosol was added. With rat liver mitochondria, half of the preformed acetoacetate was converted into 3-hydroxybutyrate after anaerobic incubation. 5. Measurement of ketone bodies by using specific enzymic methods (Williamson, Mellanby & Krebs, 1962) showed that blood of normal sheep and cattle has a high [3-hydroxybutyrate]/[acetoacetate] ratio, in contrast with that of non-ruminants (rats and pigeons). This ratio in the blood of lambs was similar to that of non-ruminants. The ratio in sheep blood decreased on starvation and rose again on re-feeding. 6. The physiological implications of the low activity of 3-hydroxybutyrate dehydrogenase in sheep liver and the fact that it is found in the cytoplasm in sheep liver and kidney cortex are discussed.

Acetoacetates↗
PubMed1970

Fatty acid metabolism in the perfused rat liver.

1. The formation of acetoacetate, beta-hydroxybutyrate and glucose was measured in the isolated perfused rat liver after addition of fatty acids. 2. The rates of ketone-body formation from ten fatty acids were approximately equal and independent of chain length (90-132mumol/h per g), with the exception of pentanoate, which reacted at one-third of this rate. The [beta-hydroxybutyrate]/[acetoacetate] ratio in the perfusion medium was increased by long-chain fatty acids. 3. Glucose was formed from all odd-numbered fatty acids tested. 4. The rate of ketone-body formation in the livers of rats kept on a high-fat diet was up to 50% higher than in the livers of rats starved for 48h. In the livers of fat-fed rats almost all the O(2) consumed was accounted for by the formation of ketone bodies. 5. The ketone-body concentration in the blood of fat-fed rats rose to 4-5mm and the [beta-hydroxybutyrate]/[acetoacetate] ratio rose to 11.5. 6. When the activity of the microsomal mixed-function oxidase system, which can bring about omega-oxidation of fatty acids, was induced by treatment of the rat with phenobarbitone, there was no change in the ketone-body production from fatty acids, nor was there a production of glucose from even-numbered fatty acids. The latter would be expected if omega-oxidation occurred. Thus omega-oxidation did not play a significant role in the metabolism of fatty acids. 7. Arachidonate was almost quantitatively converted into ketone bodies and yielded no glucose, demonstrating that gluconeogenesis from poly-unsaturated fatty acids with an even number of carbon atoms does not occur. 8. The rates of ketogenesis from unsaturated fatty acids (sorbate, undecylenate, crotonate, vinylacetate) were similar to those from the corresponding saturated fatty acids. 9. Addition of oleate together with shorter-chain fatty acids gave only a slightly higher rate of ketone-body formation than oleate alone. 10. Glucose, lactate, fructose, glycerol and other known antiketogenic substances strongly inhibited endogenous ketogenesis but had no effects on the rate of ketone-body formation in the presence of 2mm-oleate. Thus the concentrations of free fatty acids and of other oxidizable substances in the liver are key factors determining the rate of ketogenesis.

Acetoacetates↗
PubMed1974

Regulation of glucose and ketone-body metabolism in brain of anaesthetized rats.

1. The effects of starvation and diabetes on brain fuel metabolism were examined by measuring arteriovenous differences for glucose, lactate, acetoacetate and 3-hydroxybutyrate across the brains of anaesthetized fed, starved and diabetic rats. 2. In fed animals glucose represented the sole oxidative fuel of the brain. 3. After 48h of starvation, ketone-body concentrations were about 2mm and ketone-body uptake accounted for 25% of the calculated O(2) consumption: the arteriovenous difference for glucose was not diminished, but lactate release was increased, suggesting inhibition of pyruvate oxidation. 4. In severe diabetic ketosis, induced by either streptozotocin or phlorrhizin (total blood ketone bodies >7mm), the uptake of ketone bodies was further increased and accounted for 45% of the brain's oxidative metabolism, and the arteriovenous difference for glucose was decreased by one-third. The arteriovenous difference for lactate was increased significantly in the phlorrhizin-treated rats. 5. Infusion of 3-hydroxybutyrate into starved rats caused marked increases in the arteriovenous differences for lactate and both ketone bodies. 6. To study the mechanisms of these changes, steady-state concentrations of intermediates and co-factors of the glycolytic pathway were determined in freeze-blown brain. 7. Starved rats had increased concentrations of acetyl-CoA. 8. Rats with diabetic ketosis had increased concentrations of fructose 6-phosphate and decreased concentrations of fructose 1,6-diphosphate, indicating an inhibition of phosphofructokinase. 9. The concentrations of acetyl-CoA, glycogen and citrate, a potent inhibitor of phosphofructokinase, were increased in the streptozotocin-treated rats. 10. The data suggest that cerebral glucose uptake is decreased in diabetic ketoacidosis owing to inhibition of phosphofructokinase as a result of the increase in brain citrate. 11. The inhibition of brain pyruvate oxidation in starvation and diabetes can be related to the accelerated rate of ketone-body metabolism; however, we found no correlation between the decrease in glucose uptake in the diabetic state and the arteriovenous difference for ketone bodies. 12. The data also suggest that the rates of acetoacetate and 3-hydroxybutyrate utilization by brain are governed by their concentrations in plasma. 13. The finding of very low concentrations of acetoacetate and 3-hydroxybutyrate in brain compared with plasma suggests that diffusion across the blood-brain barrier may be the rate-limiting step in their metabolism.

Acetoacetates↗
PubMed1978

Aerobic glycolysis and lymphocyte transformation.

1. The role of enhanced aerobic glycolysis in the transformation of rat thymocytes by concanavalin A has been investigated. Concanavalin A addition doubled [U-(14)C]glucose uptake by rat thymocytes over 3h and caused an equivalent increased incorporation into protein, lipids and RNA. A disproportionately large percentage of the extra glucose taken up was converted into lactate, but concanavalin A also caused a specific increase in pyruvate oxidation, leading to an increase in the percentage contribution of glucose to the respiratory fuel. 2. Acetoacetate metabolism, which was not affected by concanavalin A, strongly suppressed pyruvate oxidation in the presence of [U-(14)C]glucose, but did not prevent the concanavalin A-induced stimulation of this process. Glucose uptake was not affected by acetoacetate in the presence or absence of concanavalin A, but in each case acetoacetate increased the percentage of glucose uptake accounted for by lactate production. 3. [(3)H]Thymidine incorporation into DNA in concanavalin A-treated thymocyte cultures was sensitive to the glucose concentration in the medium in a biphasic manner. Very low concentrations of glucose (25mum) stimulated DNA synthesis half-maximally, but maximum [(3)H]thymidine incorporation was observed only when the glucose concentration was raised to 1mm. Lactate addition did not alter the sensitivity of [(3)H]-thymidine uptake to glucose, but inosine blocked the effect of added glucose and strongly inhibited DNA synthesis. 4. It is suggested that the major function of enhanced aerobic glycolysis in transforming lymphocytes is to maintain higher steady-state amounts of glycolytic intermediates to act as precursors for macromolecule synthesis.

Acetoacetates↗
PubMed1984

Proton-nuclear-magnetic-resonance studies of serum, plasma and urine from fasting normal and diabetic subjects.

Resonances for the ketone bodies 3-D-hydroxybutyrate, acetone and acetoacetate are readily detected in serum, plasma and urine samples from fasting and diabetic subjects by 1H n.m.r. spectroscopy at 400 MHz. Besides the simultaneous observation of metabolites, the major advantage of n.m.r. is that little or no pretreatment of samples is required. N.m.r. determinations of 3-D-hydroxybutyrate, acetoacetate, lactate, valine and alanine were compared with determinations made with conventional assays at six 2-hourly intervals after insulin withdrawal from a diabetic subject. The n.m.r. results closely paralleled those of other assays although, by n.m.r., acetoacetate levels continued to rise rather than reaching a plateau 4h after insulin withdrawal. The 3-D-hydroxybutyrate/acetoacetate ratio in urine during withdrawal gradually increased to the value observed in plasma (3.0 +/- 0.2) as determined by n.m.r. The acetoacetate/acetone ratio in urine (17 +/- 6) was much higher than in plasma (2.5 +/- 0.7). Depletion of a mobile pool of fatty acids in plasma during fasting, as seen by n.m.r., paralleled that seen during insulin withdrawal. These fatty acids were thought to be largely in chylomicrons, acylglycerols and lipoproteins, and were grossly elevated in plasma samples from a non-insulin-dependent diabetic and in cases of known hyperlipidaemia.

3-Hydroxybutyric Acid↗
PubMed1984

Competition among oxidizable substrates in brains of young and adult rats. Dissociated cells.

The rates of conversion of D-(-)-3-hydroxy[3-14C]butyrate, [3-14C]acetoacetate, [6-14C]glucose and [U-14C]glutamine into 14CO2 were measured in the presence and absence of alternative oxidizable substrates in intact dissociated cells from the brains of young and adult rats. When unlabelled glutamine was added to [6-14C]glucose or unlabelled glucose was added to [U-14C]glutamine, the rate of 14CO2 production was decreased in both young and adult rats. The rate of oxidation of 3-hydroxy[3-14C]butyrate was also decreased by the addition of unlabelled glutamine in both age groups, but in the reverse situation, i.e. unlabelled 3-hydroxybutyrate added to [U-14C]glutamine, only the brain cells from young rats were affected. No significant effects were seen when glutamine and acetoacetate were combined. The addition of either of the two ketone bodies to [6-14C]glucose markedly lowered the rate of 14CO2 production in young rats, but in the adult only 3-hydroxybutyrate was effective and the magnitude of decrease in the rate of [6-14C]glucose oxidation was much lower than in young animals. Unlabelled glucose decreased the rate of [3-14C]acetoacetate oxidation to a minor extent in brain cells from both age groups; when added to 3-hydroxy[3-14C]butyrate, glucose had no effect in young rats and greatly enhanced 14CO2 production in adult brain cells. Many of these patterns of substrate interaction in dissociated brain cells differ from those in whole homogenates; they may be a function of the plasma membranes and the role of a carrier-mediated transport system or a reflection of a difference in the population of cell types or subcellular organelles in these two preparations.

3-Hydroxybutyric Acid↗
PubMed2000

Non-specific immunity and ketone bodies. II: In vitro studies on adherence and superoxide anion production in ovine neutrophils.

The effects of the ketone bodies beta-OH-butyrate and acetoacetate (2.4 or 4.8 mmol/l), administered singly or simultaneously in vitro, on adherence and superoxide anion (SO) production in ovine neutrophils were investigated by simultaneous assay in 96-well microplates. Because the acetoacetate used was a lithium salt, the effect of 2.4 and 4.8 mmol/l lithium chloride was also tested. Neutrophils from eight non-lactating, non-pregnant ewes were used. SO release from neutrophils was found to be very low in basal conditions and was apparently not stimulated by contact with plastic. Administration of 10(-7) mol/l phorbol myristate acetate (PMA) caused a rapid increase and release of SO production, but smaller than that induced by co-stimulation with plastic and 10(-7) mol/l PMA. LiCl (2.4 and 4.8 mmol/l) significantly increased PMA-stimulated release, but inhibited plastic and PMA co-stimulated SO release. Administration of 2.4 mmol/l ketone bodies inhibited plastic and PMA-costimulated SO release, but the effect of acetoacetate could be due to the lithium component. Administration of 4.8 mmol/l ketone bodies had no effect. Adherence was significantly increased by contact with plastic, and moreover by 10(-7) mol/l PMA. The effect was similar when PMA was acting alone or with plastic. Neither basal nor stimulated adherence were affected by 2.4 or 4.8 mmol/l ketone bodies. LiCl at a concentration of 4.8 mmol/l increased PMA and plastic co-stimulated adherence. The results suggest that, in sheep, only the ketone body beta-OH butyrate at concentrations seen in mild ketosis, could decrease bactericidal activity, while adherence is not affected. In addition to other factors that could impair the efficiency of the immune system in ketotic ruminants, the reduced bactericidal activity may contribute to the higher occurrence of infectious disease in these animals.

3-Hydroxybutyric Acid↗
PubMed1995

Generation of ketone bodies from leucine by cultured astroglial cells.

To elucidate the significance of branched-chain amino acids (BCAAs) for brain energy metabolism, the capacity to use BCAAs for oxidative metabolism was investigated in astroglia-rich primary cultures derived from newborn rat brain. The cells selectively removed BCAAs from the culture medium, the disappearance following first-order kinetics. The BCAAs disappeared rapidly in spite of the presence of sufficient glucose as substrate for the generation of energy. Taking into consideration that the ketogenic amino acid leucine could be degraded only to acetyl-CoA and acetoacetate, and with the knowledge that astroglial cells have the capacity to secrete ketone bodies, this amino acid was chosen for further metabolic studies. After incubation of the cells with leucine, acetoacetate, D-beta-hydroxybutyrate, and alpha-ketoisocaproate were found to have accumulated in the culture medium. Identification of the radioactive metabolites generated from [4,5-3H]leucine established that the source of the substances released was indeed leucine. These results indicate that, at least in culture, astroglial cells degrade leucine via the known metabolite alpha-ketoisocaproate, to acetoacetate, which can be further reduced to D-beta-hydroxybutyrate. It is hypothesized that upon release from brain astrocytes, the ketone bodies could serve as fuel molecules for neighboring cells such as neurons and oligodendrocytes. In view of these and other results, astrocytes may be considered the brain's fuel processing plants.

3-Hydroxybutyric Acid↗
PubMed1981

Ketone-body metabolism in glioma and neuroblastoma cells.

We have examined the metabolism of ketone bodies in neuroblastoma C1300 and glioma C6 cells, two established lines of neural origin. The three ketone body-metabolizing enzymes are present in cells of both lines in the relative proportions normally found in brain (D-3-hydroxybutyrate dehydrogenase less than acetoacetyl-CoA thiolase less than 3-ketoacid CoA-transferase), the activities of the first two are higher in glioma cells than in neuroblastoma, and that of the third is 2-fold higher in neuroblastoma cells than in glioma cells. The specific activity of 3-ketoacid CoA-transferase (EC 2.8.3.5) in both cell lines increased as the cultures achieved confluence, then decreased. Ketone bodies and especially acetoacetate are preferred substrates for synthesis of neural lipids in cells of both lines. The incorporation of glucose carbon into lipids is significantly reduced in cells of both lines in the presence of ketone bodies. Addition of acetoacetate but not DL-3-hydroxybutyrate to the culture medium resulted in a significant increase in the activity of 3-ketoacid CoA-transferase and also in the rate of acetoacetate oxidation in neuroblastoma cells but not glioma cells. These findings indicate that specific differences exist in the capacity of these two cell lines to metabolize ketone bodies and also that substrate-level regulation of the ketone body-metabolizing pathway exists. These two lines therefore provide a potentially useful system in which the mechanisms of regulation of these enzymes may be examined.

3-Hydroxybutyric Acid↗
PubMed1978

Intravenous feeding of the rat with short chain fatty acid esters. II. Monoacetoacetin.

Acetoacetic acid is oxidized independent of carnitine transport into the cell mitochondria and its monoglyceride is a water soluble compound. The latter was examined as an intravenous nutrient. The monoglyceride of acetoacetic acid was prepared from the acid anhydride, diketene, and glycerol and was found to be totally miscible with water. The nutritional properties of monoacetoacetin were investigated by continuous intravenous infusion of 25 or 50 g/kg body weight per day into ad libitum fed rats. The response of these animals was compared to normal and food restricted rats. All experimental animals survived the 7 day study period in good health and were free of detectable physiological and behavioral abnormalities. The test rats demonstrated weight gain dependent on the infusion rate while on an inadequate spontaneous oral food intake diet. Ketonuria, hyperketonemia and monoglyceride excretion in the urine accompanied the infusion of monoacetoacetin and were dependent on the infusion load. At 50 g/kg per day total plasma ketones were found to be comparable with the infusion load. At 50 g/kg per day total plasma ketones were found to be comparable with the maximum level obtained in fasted rats, but the acetoacetate concentration was relatively higher than in fasting. This was consistant with ketosis derived from the hydrolysis of the monoglyceride. It was concluded from these results that monoacetoacetin might be an asset for intravenous nutrition.

Acetoacetates↗
PubMed1985

Simultaneous determination of ketone bodies in biological samples by gas chromatographic headspace analysis.

A method is described on gas chromatographic headspace analysis for the determination of the physiological ketone bodies: acetone, acetoacetate and beta-hydroxybutyrate. The procedure proposed involves quantitative conversion of both acetoacetate by decarboxylation in a strong acidic medium, and beta-hydroxybutyrate by oxidation to acetoacetate and decarboxylation to acetone, which is then quantified chromatographically. The successful application of the method is illustrated by the values of ketone bodies in plasma, kidney, lung, and liver of fed and 48-hr-fasted rats.

3-Hydroxybutyric Acid↗
PubMed1986

Effects of fasting on ketone body concentrations in healthy men of different ages.

This work was performed to assess age effects on fasting-induced hyperketonemia and to determine if measurement of cerebral glucose utilization by positron emission tomography after 6 to 8 hr of fasting is associated with hyperketonemia that could influence cerebral glucose metabolism. Acetoacetate and 3-hydroxybutyrate were assayed in venous blood from healthy men of various ages, subjected to an 18-hr fast. At 18 hr of fasting but not at 14 hr or earlier, 3-hydroxybutyrate concentrations were correlated significantly with age; concentrations of acetoacetate and 3-hydroxybutyrate were significantly higher than at earlier times in the fast, p less than or equal to .05, with elevations of 82% and 214% over baseline, respectively. Acetoacetate and 3-hydroxybutyrate concentrations were higher on the day when cerebral glucose utilization was determined than after a comparable fast at another time. The observed level of hyperketonemia, however, would not substantially influence cerebral glucose metabolism. The findings indicate that aging is associated with increased susceptibility to fasting-induced hyperketonemia.

3-Hydroxybutyric Acid↗
PubMed1982

Purification and properties of succinyl-CoA:3-oxo-acid CoA-transferase from rat brain.

Rat brain succinyl-CoA:3-oxo-acid CoA-transferase (3-oxo-acid CoA-transferase, EC 2.8.3.5), the first committed enzyme in the oxidation of ketone bodies in mitochondria, was purified to apparent homogeneity as judged by polyacrylamide gel electrophoresis. The enzyme has an apparent molecular weight of 90,000 as determined by G-150 Sephadex chromatography, and an apparent subunit molecular weight of 53,000 as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The specific activity of the purified enzyme was approximately 161 mumol/min/mg of protein. Initial velocity studies of the forward reaction (acetoacetate leads to acetoacetyl-CoA) are consistent with a "ping pong" mechanism. Substrate inhibition appears above approximately 1 mM acetoacetate. Apparent Km values were 70 microM for acetoacetate and 156 microM for succinyl-CoA (the forward reaction), and 59 microM for acetoacetyl-CoA and 25 mM for succinate (the reverse reaction). These values are markedly different from those reported for this enzyme from pig heart.

Acetoacetates↗
PubMed1976

Cerebral blood flow and exchange of oxygen, glucose, ketone bodies, lactate, pyruvate and amino acids in infants.

Cerebral blood flow (CBF) and cerebral av-differences of oxygen and circulating substrates were measured in normocapnic infants during general anaesthesia before elective surgery in order to study possible age-dependent variations. CBF was determined by a minor modification of the Kety-Schmidt technique from desaturation curves of nitrous oxide (N2O) in arterial and cerebral venous blood (N2O analysed by gas chromatography on 15 mul blood samples) after reduction of inhaled N2O from 75 to 50%. The reproducibility was +/-4.6%. Lactate, pyruvate and oxygen were determined in whole blood and amino acids in plasma by ion-exchange chromatography. Reliable av-differences of glucose, acetoacetate and D-beta-hydroxybutyrate could be calculated from plasma values and hematocrits. Mean values from 12 infants (age 11 days-12 months) were: CBF 69 ml/100 g0min-1; cerebral uptake (in mumoles/100 g-min-1): oxygen 104, glucose 27, acetoacetate 0.9, D-beta-hydroxybutyrate 2.3; cerebral release: lactate 2.4 and pyruvate 0.8. Significant uptake of amino acids was found only for histidine 0.95 and arginine 0.7. Significant correlations between arterial concentration and cerebral exchange were found for: ornithine, arginine, phenylalanine, aspartic acid, serine, glutamine and acetoacetate. CBF and substrate exchange were unrelated to age within the group. Infants had higher mean CBF and greater uptake of ketone bodies than has been reported in adults.

Acetoacetates↗
PubMed1975

Exercise-induced increase in the capacity of rat skeletal muscle to oxidize ketones.

During and after strenuous prolonged exercise, sedentary individuals develop high blood levels of acetoacetate and beta-hydroxybutyrate whereas exercise-trained animals and human subjects do not. We have investigated the possibility that exercise training can increase the capacity of skeletal muscle to oxidize ketones. In this study we measured rates of D-beta[3-14-C]-hydroxybutyrate and [3-14-C]acetoacetate oxidation, and the levels of activity of the enzymes involved in the oxidation of ketones in homogenates of gastrocnemius muscles of exercise-trained and of untrained male rats. The trained animals had markedly lower blood ketone levels immediately and 60 min after a 90 min long bout of exercise than did the sedentary animals. The rates of D-beta-[13-14C]hydroxybutryate and [3-14-C]acetoacetate oxidation were twice as high in homogenates of muscles from the trained as compared to the sedentary rats. The increases in levels of activity in gastrocnemius muscle in response to the exercise program were: beta-hydroxybutyrate dehydrogenase threefold; 3-ketoacid CoA-transferase twofold; and acetoacetyl-CoA thiolase 55%. This exercise-induced increase in the capacity of skeletal muscle to oxidize ketones could play a role in preventing development of ketosis in the physically trained animal during and following prolonged strenuous exercise.

Acetoacetates↗