Ketogenesis and its regulation

The Metabolic Syndrome, a Human Disease

This review focuses on the question of metabolic syndrome (MS) being a complex, but essentially monophyletic, galaxy of associated diseases/disorders, or just a syndrome of related but rather independent pathologies. The human nature of MS (its exceptionality in Nature and its close interdependence with human action and evolution) is presented and discussed. The text also describes the close interdependence of its components, with special emphasis on the description of their interrelations (including their syndromic development and recruitment), as well as their consequences upon energy handling and partition. The main theories on MS's origin and development are presented in relation to hepatic steatosis, type 2 diabetes, and obesity, but encompass most of the MS components described so far. The differential effects of sex and its biological consequences are considered under the light of human social needs and evolution, which are also directly related to MS epidemiology, severity, and relations with senescence. The triggering and maintenance factors of MS are discussed, with especial emphasis on inflammation, a complex process affecting different levels of organization and which is a critical element for MS development. Inflammation is also related to the operation of connective tissue (including the adipose organ) and the widely studied and acknowledged influence of diet. The role of diet composition, including the transcendence of the anaplerotic maintenance of the Krebs cycle from dietary amino acid supply (and its timing), is developed in the context of testosterone and β-estradiol control of the insulin-glycaemia hepatic core system of carbohydrate-triacylglycerol energy handling. The high probability of MS acting as a unique complex biological control system (essentially monophyletic) is presented, together with additional perspectives/considerations on the treatment of this 'very' human disease.

Utility of Postmortem Vitreous Beta-Hydroxybutyrate Testing for Distinguishing Sudden from Prolonged Deaths and for Diagnosing Ketoacidosis

A retrospective, cross-sectional analysis of vitreous beta-hydroxybutyrate (BHB) on 967 forensic cases over a two-year period was conducted. Cases were sorted into six categories of death: (i) sudden traumatic/non-natural (ST), (ii) sudden natural (SN), (iii) prolonged traumatic/non-natural (PT), (iv) prolonged natural (PN), (v) diabetic ketoacidosis (DKA), and (vi) alcoholic ketoacidosis (AKA). The mean BHB for all cases was 1.67 mmol/L (17.4 mg/dL; range: 0.11-18.02 mmol/L). The numbers of DKA, AKA, PN, PT, SN, and ST deaths were 21, 5, 155, 258, 275, and 253, respectively. Their mean vitreous BHBs were as follows: 11.04 mmol/L (DKA), 8.88 mmol/L (AKA), 1.56 mmol/L (PN), 1.55 mmol/L (PT), 1.26 mmol/L (SN), and 1.38 mmol/L (ST). There was a statistically significant difference between the mean BHBs of the PN and SN death groups (p < 0.001), as well as between those of the PT and ST death groups (p = 0.004). Given the overlapping ranges seen between the prolonged and sudden death groups, the identified differences did not hold clinical significance. In addition, we sought to determine a threshold value for vitreous BHB to definitely diagnose cases of ketoacidosis. BHB threshold concentrations between 2.5 and 5 mmol/L produced sensitivities >92% and specificities >96%. A receiver operator characteristic curve found 3.43 mmol/L to be the optimal cutoff value, demonstrating a specificity of 98.3% and a sensitivity of 96.2%.

Does acid-base equilibrium correlate with remnant liver volume during stepwise liver resection?

Small for size and flow syndrome (SFSF) is one of the most challenging complications following extended hepatectomy (EH). After EH, hepatic artery flow decreases and portal vein flow increases per 100 g of remnant liver volume (RLV). This causes hypoxia followed by metabolic acidosis. A correlation between acidosis and posthepatectomy liver failure has been postulated but not studied systematically in a large animal model or clinical setting. In our study, we performed stepwise liver resections on nine pigs to defined SFSF limits as follows: step 1: segment II/III resection, step 2: segment IV resection, step 3: segment V/VIII resection (RLV: 75, 50, and 25%, respectively). Blood gas values were measured before and after each step using four catheters inserted into the carotid artery, internal jugular vein, hepatic artery, and portal vein. The pH, [Formula: see text], and base excess (BE) decreased, but [Formula: see text] values increased after 75% resection in the portal and jugular veins. EH correlated with reduced BE in the hepatic artery. Pco₂ values increased after 75% resection in the jugular vein. In contrast, arterial Po₂ increased after every resection, whereas the venous Po₂ decreased slightly. There were differences in venous [Formula: see text], BE in the hepatic artery, and Pco₂ in the jugular vein after 75% liver resection. Because 75% resection is the limit for SFSF, these noninvasive blood evaluations may be used to predict SFSF. Further studies with long-term follow-up are required to validate this correlation.NEW & NOTEWORTHY This is the first study to evaluate acid-base parameters in major central and hepatic vessels during stepwise liver resection. The pH, [Formula: see text], and base excess (BE) decreased, but [Formula: see text] values increased after 75% resection in the portal and jugular veins. Extended hepatectomy correlated with reduced BE in the hepatic artery. Because 75% resection is the limit for small for size and flow syndrome (SFSF), postresection blood gas evaluations may be used to predict SFSF.

Ribosomal protein-Mdm2-p53 pathway coordinates nutrient stress with lipid metabolism by regulating MCD and promoting fatty acid oxidation

The tumor suppressor p53 has recently been shown to regulate energy metabolism through multiple mechanisms. However, the in vivo signaling pathways related to p53-mediated metabolic regulation remain largely uncharacterized. By using mice bearing a single amino acid substitution at cysteine residue 305 of mouse double minute 2 (Mdm2(C305F)), which renders Mdm2 deficient in binding ribosomal proteins (RPs) RPL11 and RPL5, we show that the RP-Mdm2-p53 signaling pathway is critical for sensing nutrient deprivation and maintaining liver lipid homeostasis. Although the Mdm2(C305F) mutation does not significantly affect growth and development in mice, this mutation promotes fat accumulation under normal feeding conditions and hepatosteatosis under acute fasting conditions. We show that nutrient deprivation inhibits rRNA biosynthesis, increases RP-Mdm2 interaction, and induces p53-mediated transactivation of malonyl-CoA decarboxylase (MCD), which catalyzes the degradation of malonyl-CoA to acetyl-CoA, thus modulating lipid partitioning. Fasted Mdm2(C305F) mice demonstrate attenuated MCD induction and enhanced malonyl-CoA accumulation in addition to decreased oxidative respiration and increased fatty acid accumulation in the liver. Thus, the RP-Mdm2-p53 pathway appears to function as an endogenous sensor responsible for stimulating fatty acid oxidation in response to nutrient depletion.

Ketogenic enteral nutrition as a treatment for obesity: short term and long term results from 19,000 patients

Background

Only protein diet has been used successfully to prevent loss of lean body mass first in post-surgical and then in obese patients. We studied overweight and obese patients receiving short treatments of an exclusively protein-based nutritional solution as 24-hour enteral infusion.

Methods

19,036 patients (age 44.3 ± 13, M:F = 2:5) with an initial body mass index of 36.5 ± 7.1 underwent 10-day cycles of enteral nutrition through a fine nasogastric tube. The nutritional solution consisted solely of 50–65 g of proteins, plus vitamins and electrolytes. The 24-hour infusion was controlled with a small portable pump. Before and after each 10-day cycle body composition was checked with a Handy 3000 impedance analyzer. At the onset of treatment, average fat mass was 40.9 ± 12.8 kg while body cell mass was 42.7 ± 7.2 kg in males and 27.4 ± 4.6 kg in females.

Results

After an average of 2.5 cycles the patients lost 10.2 ± 7.0 kg of body weight, 5.8 ± 5.5 kg of fat mass and 2.2 ± 3.3 kg of body cell mass. No significant adverse effects were recorded except asthenia and constipation which were easily controlled with therapy. Long-term results were obtained from 15,444 patients and after an average of 362 ± 296 days we found a mean weight regain of 15.4%.

Conclusion

Ketogenic Enteral Nutrition treatment of over 19,000 patients induced a rapid 10% weight loss, 57% of which was Fat Mass. No significant adverse effects were found. The treatment is safe, fast, inexpensive and has good one-year results for weight maintenance.

Acyl-CoA binding proteins: multiplicity and function

The physiological role of long-chain fatty acyl-CoA is thought to be primarily in intermediary metabolism of fatty acids. However, recent data show that nM to microM levels of these lipophilic molecules are potent regulators of cell functions in vitro. Although long-chain fatty acyl-CoA are present at several hundred microM concentration in the cell, very little long-chain fatty acyl-CoA actually exists as free or unbound molecules, but rather is bound with high affinity to membrane lipids and/or proteins. Recently, there is growing awareness that cytosol contains nonenzymatic proteins also capable of binding long-chain fatty acyl-CoA with high affinity. Although the identity of the cytosolic long-chain fatty acyl-CoA binding protein(s) has been the subject of some controversy, there is growing evidence that several diverse nonenzymatic cytosolic proteins will bind long-chain fatty acyl-CoA. Not only does acyl-CoA binding protein specifically bind medium and long-chain fatty acyl-CoA (LCFA-CoA), but ubiquitous proteins with multiple ligand specificities such as the fatty acid binding proteins and sterol carrier protein-2 also bind LCFA-CoA with high affinity. The potential of these acyl-CoA binding proteins to influence the level of free LCFA-CoA and thereby the amount of LCFA-CoA bound to regulatory sites in proteins and enzymes is only now being examined in detail. The purpose of this article is to explore the identity, nature, function, and pathobiology of these fascinating newly discovered long-chain fatty acyl-CoA binding proteins. The relative contributions of these three different protein families to LCFA-CoA utilization and/or regulation of cellular activities are the focus of new directions in this field.

A simple method to fix and extract ATP from rat liver samples

A simple one-step method to fix and extract ATP from rat liver samples is described. The results show that this method is suitable for fixation and extraction of the hepatic ATP content, whereas its simplicity leads to consider it the procedure of choice.

Alcoholic ketoacidosis: a case report

A 43-year-old alcoholic presented in coma with ketoacidosis, after three days of nausea and feeling generally unwell, which had been preceded by a prolonged three-week period of heavy alcohol consumption with poor dietary intake. The acidosis responded rapidly to intravenous dextrose. This is the first Scottish report of a case of alcoholic ketoacidosis.

Hepatic carnitine palmitoyltransferase turnover and translation rates in fed, starved, streptozotocin-diabetic and diethylhexyl phthalate-treated rats

Hepatic carnitine palmitoyltransferase (CPT) turnover was studied in control and in non-ketotic hyperglycaemic streptozotocin-diabetic rats. The degradation constant (kd) and half-life (t1/2) did not appear to be altered by mild diabetes. The hepatic CPT (micrograms/g of liver) was not increased by the mild, non-ketotic, diabetes. However, the total hepatic CPT (micrograms/liver) was 37% greater in the diabetic animals, owing to the increased liver weight. This resulted from a 40% increase in the synthesis constant (ks). Hepatic CPT activity (total detergent-solubilized) and translation rates were measured in fed, starved (48 h), non-ketotic diabetic, ketotic diabetic and diethylhexyl phthalate (DEHP)-treated rats. CPT activity (m units/mg of mitochondrial protein) was not significantly increased with non-ketotic diabetes (44% increase, but non-significant), but was increased approx. 2-fold with starvation and ketotic diabetes, and 3.5-fold with DEHP treatment. CPT expressed as units/liver was increased non-significantly (23%) in non-ketotic and starved rats, similar to the turnover study, but was significantly increased with ketotic diabetes and with DEHP treatment. mRNA-translation activity for CPT was elevated in all states to a somewhat greater extent than was activity. It was concluded that protein synthesis as a product of increased CPT-mRNA translation activity is a major means of long-term regulation.

Stimulation by acetoacetate of hepatic triacylglycerol synthesis

The factors responsible for the huge accumulation of hepatic triacylglycerols in the ketotic diabetic state are not established. Our earlier work suggested a role for ketone bodies in the increased hepatic triacylglycerol synthesis observed in the ketotic diabetic state. Isolated hepatocytes obtained from normal fed rats were incubated with sodium acetoacetate or sodium chloride (control) and [1-14C]palmitate in Krebs-albumin buffer. Acetoacetate stimulated triacylglycerol synthesis in a concentration-dependent manner without increasing palmitate uptake or inhibiting palmitate oxidation. Beta hydroxybutyrate showed no effect on palmitate esterification to triacylglycerols. Isolated hepatocytes of normal fed rats were incubated with either sodium acetoacetate or sodium chloride and the nuclear-free homogenate was incubated with [U-14C]glycero-3-phosphate and cofactors. The synthesis of triacylglycerol and the activity of the cytosolic phosphatidate phosphohydrolase were increased in the cells pre-incubated with acetoacetate. The results of this study demonstrate that the increases in triacylglycerol synthesis and the cytosolic activity of phosphatidate phosphohydrolase previously observed by us in the ketotic diabetic liver, could be reproduced in normal fed rat liver cells by incubating them with acetoacetate. The results identify acetoacetate as a potential factor, in the regulation of hepatic triacylglycerol synthesis and for hepatic accumulation of triacylglycerols observed in the ketotic diabetic state.

Metabolic pathways for ketone body production. 13C NMR spectroscopy of rat liver in vivo using 13C-multilabeled fatty acids

The hormonal regulation of ketogenesis in the liver of living rat has been studied noninvasively with 13C nuclear magnetic resonance. The protocol involved the use of a surface coil that was placed on the skin of the rat, directly over the normal location of the liver. Signals from superficial tissue were suppressed with a 180 degrees pulse at the center of the coil. A resolution of 0.6 ppm was obtained in the 13C NMR spectra at 20.1 MHz, which was equal to or better than that observed in experiments where the liver was surgically exposed and surrounded with radiofrequency coil. The spatial selection for the liver was better than 90%, with extrahepatic adipose tissue contributing only a very small amount of signal. The metabolic activities of the liver were investigated by infusion of 13C-labeled butyrate in the jugular vein of the anesthetized rat. The rate of butyrate infusion was chosen to be close to the maximum oxidative capacity of the rat liver, and the 13C signal intensities were enhanced by using doubly labeled [1,3-13C]butyrate as a substrate. Different 13C NMR spectra and hence different metabolites were observed depending on the hormonal state of the animal. In the fasted rat, the most intense 13C signal came from the end product of the Krebs cycle, namely, HCO3, with additional resonances from glutamine and glutamate. Weak resonances of the ketone bodies 3-hydroxybutyrate and acetoacetate could also be detected and allowed an evaluation of the "redox state" of the in vivo liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Dual effects of calcium on the oxidation of fatty acids to ketone bodies in liver mitochondria

The addition of calcium ions (Ca2+) to rat liver mitochondria, under conditions of rapid accumulation of 10-40 nmol Ca2+/mg protein, inhibited the oxidation of long and medium chain fatty acids to ketone bodies, whereas higher quantities of Ca2+ activated the process. The mitochondrial NADH:NAD ratio exhibited corresponding depression and elevation. Both inhibitory and stimulatory actions of Ca2+ were operative in liver mitochondria from fed and fasted rats and appear to be localized in the mitochondrial inner membrane-matrix region. These observations may signify involvement of Ca2+ in the regulation of fatty acid oxidation and ketogenesis.

Interrelationships between 3-hydroxy-3-methylglutaryl-CoA synthase, acetoacetyl-CoA and ketogenesis

Kinetic and physical approaches have been employed to investigate the binding of acetoacetyl-CoA to hydroxymethylglutaryl-CoA synthase. The enzyme has an apparent Km for acetoacetyl-CoA (0.35 microM) which is more than an order of magnitude lower than the Ki (6--10 microM) measured for substrate inhibition by this metabolite. Hepatic acetoacetyl-CoA concentration, as measured by a sensitive and highly specific radioactive assay appears to be in the 1--10 microM range; the concentration decreases during diabetic ketoacidosis. Total hepatic activity of hydroxymethylglutaryl-CoA synthase and levels of mitochondrial enzyme protein, determined by radioimmunoassay, are not appreciably different in livers from control or ketoacidotic animals. In contrast to the decrease in hepatic acetoacetyl-CoA concentration observed during ketoacidosis, myocardial acetoacetyl-CoA levels are increased by at least tenfold when compared to controls. Elevated acetoacetyl-CoA levels may serve to inhibit fatty acid utilization by the heart. Thus, a consideration of the multiple interactions of acetoacetyl-CoA with the enzymes involved in ketone body production and utilization may be useful in evaluating the metabolic significance of this intermediate.

The role of glucagon in the regulation of plasma lipids

The role of glucagon in regulating plasma lipid concentrations (nonesterified fatty acids, ketone bodies, and triglycerides) is reviewed. The effects of glucagon-induced insulin secretion upon this lipid regulation are discussed that may resolve conflicting reports in the literature are resolved. In addition, the unresolved problem concerning the pharmacologic versus physiologic effects of glucagon is stressed. Glucagon's role in stimulating lipolysis at the adipocyte serves two important functions. First, it provides plasma nonesterified fatty acids for energy metabolism and secondly, it ensures substrate for hepatic ketogenesis. In vitro, glucagon's lipolytic activity has been consistently observed, but in vivo, this activity has sometimes been obscured by the effects of glucagon-induced insulin secretion. Frequently, a biphasic response has been reported in which a direct lipolytic response is followed by a glucagon-induced insulin suppression of plasma nonesterified fatty acid concentration. When the glucagon-induced insulin secretion has been controlled by various in vivo techniques, glucagon's lipolytic activity in vivo has frequently been demonstrable. In the 1960s, in vitro liver perfusion experiments demonstrated that glucagon enhanced hepatic ketogenesis independent of glucagon's lipolytic activity. However, this direct effect of glucagon on the hepatocyte was not universally accepted because of conflicting reports in the literature. Failure to observe an in vitro ketogenic effect of the hormone in some studies may have been due to suboptimal experimental conditions. Certain factors are now known to influence the ketogenic response, such as the concentration of fatty acids in the media and the nutritional status of the animal. Under optimal in vitro conditions with liver preparations from fed animals, the ketogenic response to physiologic concentrations of glucagon has been demonstrated. However, further study is necessary to define the quantitative ketogenic role of the hormone. In spite of this early in vitro work, glucagon was not definitely shown to be ketogenic in vivo (independent of fatty acid availability) both in the rat and in diabetic man until 1975. Since these observations, several reports have confirmed the ketogenic action of glucagon in vivo by direct hepatic catheterization experiments. Glucagon's role in decreasing hepatic triglyceride synthesis and secretion in vitro has been repeatedly shown but the mechanism is unresolved. This lipid regulatory action of glucagon has been more difficult to demonstrate in vivo because of the many variables that affect triglyceride synthesis. Under specific experimental conditions, however, glucagon has been shown to decrease plasma triglyceride concentration in man at both physiologic and pharmacologic concentrations. Hepatic catheterization experiments have also confirmed this effect in man. The regulation of lipids by glucagon fits well into its role as a stress hormone...

Oxaloacetate deficiency in MCT-induced ketogenesis

This study was an attempt to discover whether a deficiency in hepatic oxaloacetate can explain the acceleration of ketogenesis observed after the ingestion of medium-chain triglycerides (MCT, constituent fatty acids from C8 to C12). The method of investigation used consisted in supplying oxaloacetate (by intraperitoneal injection of oxaloacetate, aspartate, or L-tryptophan) to rats that had ingested MCT. The indirectly given oxaloacetate caused a decrease in ketone body levels in the liver. The stimulation of ketogenesis induced by an exogenous supply of MCT is therefore at least partly due to a deficiency of oxaloacetate. The results show that this can be explained both by a leakage of this metabolite into the pathway of gluconeogenesis and by its reduction into malate. Since the acetyl-CoA derived from oxidized medium-chain fatty acids cannot enter into the Krebs cycle, it is diverted to the production of ketone bodies.

The metabolism of oleic acid by the perfused rat liver in experimental diabetes induced by antiinsulin serum

The metabolism of varying quantities of oleic acid was examined in isolated perfused livers from normal fed rats and from animals made diabetic by pretreatment with guinea pig antiinsulin serum (AIS). The data presented reemphasize the fact that the quantity of free fatty acid (FFA) coming to the liver is a necessary, but not the most important, factor affecting the subsequent metabolism of the FFA. Rates of ketogenesis and output of triglyceride and the terminal concentration of hepatic triglyceride were proportional to uptake of FFA in certain concentration ranges. For equal rates of uptake of FFA, ketogenesis was greater, and the quantity of triglyceride secreted or accumulated within the liver was less, with livers from diabetic animals than with livers from normal animals. In confirmation of previous data, the liver was observed to have a maximal capacity to secrete triglyceride. Triglyceride accumulated in livers from normal-fed and diabetic animals only when uptake of FFA was more than sufficient to saturate the secretory process. Since proportionately more FFA was catabolized by livers from AIS treated animals, greater uptake of FFA was required to produce maximal rates of output of triglyceride and accumulation in livers from diabetic than from normal animals. Rates of ketogenesis by livers from normal fed animals increased minimally with increasing uptake of FFA (up to 1.0 mM free fatty acid). Even when uptake increased considerably with FFA concentrations of approximately 2.5 mM, rates of ketogenesis by livers from normal animals were less than half those of livers from diabetic rats, and maximal rates were not achieved by the normal controls. It is evident that changes in hepatic metabolism of FFA in the intact diabetic animal result from simultaneous alterations of supply of FFA and hormonally induced metabolic changes in the liver. Moreover, although hepatic secretion and accumulation of triglyceride is greater in isolated perfused livers from normal rats than from diabetic animals when the livers are exposed to equal quantities of FFA, the diabetic livers can accumulate more triglyceride, secrete more triglyceride, and oxidize more FFA to ketone bodies than can the normal under conditions in which considerably more substrate is available to the diabetic rather than to the normal livers. These differences might also be expected to occur in the acutely insulin deficient intact animal, in which changes in hormonal status and substrate (FFA) availability occur simultaneously, and might, in part, explain the ketonemia, hypertriglyceridemia, and hepatic steatosis often observed in vivo.

Evidence for a homogeneous pool of acetyl-CoA in rat-liver mitochondria

Rat-liver mitochondria oxidized [1-14C]palmitate or [U-14C]palmitate and unlabelled pyruvate in a medium containing fluorocitrate and L-carnitine. The oxidation products (acetyl-L-carnitine, ketone bodies and citrate) were separated by anion-exchange chromatography and their specific activities were determined. The distribution of radioactivity over the two halves of the ketone bodies was essayed. Significant differences between the specific activities of citrate, acetyl-L-carnitine and the carboxylhalf of the ketone bodies were not observed; this was consistently the case, even when pyruvate contributed for more than 80% to the acetyl-CoA pool. Our results argue against compartition of mitochondrial acetyl-CoA. Instead, they strongly suggest that the acetyl-CoA originating from the simultaneous oxidation of pyruvate and palmitate equilibrates before being distributed over the various pathways of further metabolism.

Gluconeogenesis in vertebrate livers

1. The hypothesis is advanced that it would be logical for a tissue (liver) to evolve as a gluconeogenic organ in order to recover the lactate produced as a result of rapid and sustained contraction of skeletal muscle. 2. Lactate was present in skeletal muscle of all animals examined and increased following electrical stimulation. It was also present in the blood. 3. Gluconeogenesis from lactate occurred in liver slices of all animals excepting amphibia. However, livers of these animals also contained much glycogen and are probably gluconeogenic. 4. Phosphoenolpyruvate carboxykinase was present in all animals investigated; pyruvate carboxylase was present in all animals excepting the toad.

Studies on the influence of fatty acids on pyruvate dehydrogenase interconversion in rat-liver mitochondria

1. The effect of fatty acids on the interconversion of pyruvate dehydrogenase between its active (nonphosphorylated) and inactive (phosphorylated) forms was measured in rat liver mitochondria respiring in state 3 with pyruvate plus malate and 2-oxoglutarate plus malate and during state 4 to state 3 transition in the presence of different substrates. The content of intramitochondrial adenine nucleotides was determined in the parallel experiments. 2. Decrease of the intramitochondrial ATP/ADP ratio with propionate and its increase with palmitoyl-L-carnitine in state 3 is accompanied by a shift of the steady-state of the pyruvate dehydrogenase system towards the active or the inactive form, respectively. 3. Transition from the high energy state (state4) to the active respiration (state3) in mitochondria oxidizing 2-oxoglutarate or plamitoyl-L-carnitine causes an increase of the amount of the active form of pyruvate dehydrogenase due to the decrease of ATP/ADP ratio in the matrix. 4. No change in ATP/ADP ratio can be observed in the presence of octanoate in mitochondria oxidizing pyruvate or 2-oxoglutarate in state 3 or during state 4 to state 3 transition. Simultanelusly, no significant change in phosphorylation state of pyruvate dehydrogenase occurs and a low amount of the enzyme in the active form is present with octanoate or octanoate plus 2-oxoglutarate. Pyruvate abolishes this effect of octanoate and shifts the steady-state of pyruvate dehydrogenase system towards the active form. 5. These results indicate that fatty acids influence the interconversion of pyruvate dehydrogenase mainly by changing intramitochondrial ATP/ADP ratio. However, the comparison of the steady-state level of the pyruvate dehydrogenase system in the presence of different substrates in various metabolic conditions provides some evidence that accumulation of acetyl-CoA and high level of NADH may promote the phosphorylation of pyruvate dehydrogenase. 6. Pyruvate exerts its protective effect against phosphorylation of pyruvate dehydrogenase in the presence of fatty acids of short, medium or long chain in a manner which depends on its concentration. It is suggested that in isolated mitochondria pyruvate counteracts the effect of acetyl-CoA and NADH on pyruvate dehydrogenase kinase.

On gluconeogenesis of human liver. Accelerated hepatic glucose formation induced by increased precursor supply

In 8 subjects in whom portal vein catheters had been inserted 5-6 days previously during cholecystectomy, arterial and portal concentrations of glucose, lactate, pyruvate, glycerol, alanine, free fatty acids, beta-hydroxybutyrate and acetoacetate revealed no significant differences. This provided the basis for the calculation of hepatic balances from arterio-hepatic venous substrate-differences in 17 healthy volunteers. In eight of them metabolic balances were determined during elevated hepatic lactate supply. Kinetics of the substrates throughout the whole test period in 9 controls showed no gross interference from the catheterization or infusion procedure. The elevated hepatic lactate concentration caused a doubling of hepatic glucose output, which could almost entirely be accounted for by a fivefold increase of hepatic lactate uptake. This acceleration of hepatic gluconeogenesis was accompanied by a significant increment of hepatic free fatty acid uptake, whereas hepatic ketone body production did not change. These data seem to support the view that hepatic energy requirements caused by an accelerated gluconeogenesis might be covered from enhanced free fatty acid oxidation.

Intermediary hepatic metabolism of rat after oral medium chain triglyceride load

Hepatic ketogenesis was studied in rats given medium chain triglycerides (MCT). Acetyl-CoA accumulated in the liver, indicating a very rapid beta-oxidation of medium chain fatty acids. Citrate level increases. Ketogenesis is strongly enhanced. Cytoplasm and particularly mitochondria are more reduced after MCT. This may explain the very high increase in hepatic malate. Under our experimental conditions, there appears to be a significant linear relationship between the hepatic acetyl-Coa level and those of total ketone bodies and malade respectively.

[Breath acetone and ketonemia in normal- and overweight subjects during total fasting (author's transl)]

In subjects of ideal weight (7 males and 7 females) total whole blood ketones and breath acetone were determined during a 6 day fast, and in obese subjects (8 males, 18 females) during 6-28 days of fasting. Development of starvation ketosis was significantly slower in overweight than in normal weight subjects. Breath acetone concentration was up to blood ketone levels of 4 mMol/1 a linear function of the blood ketone concentration, beyond that level, however, an additional exponential component became apparent. The highest acetone elimination found was 4.46 mg/min, corresponding to 6.4 g acetone and 11.2 g acetoacetic acid in 24 hours. Hence the decarboxylation of acetoacetic acid to acetone may be an additional mechanism for the lowering of ketoacidosis in starvation.

Stimulation by glucagon of the incorporation of U-14C-labeled substrates into glucose by isolated hepatocytes from fed rats

The effect of glucagon on the incorporation of U-14C-labeled lactate, pyruvate or alanine into glucose has been studied using isolated hepatocytes from livers of fed rats. Rates of incorporation into glucose were about the same as observed in perfused liver preparations provided precautions were taken to avoid depletion of certain metabolities by the preparative procedures. With each substrate, stimulation of the incorporation into glucose by a maximally effective concentration of glucagon (10 nM) was associated with about a 75% reduction in the substrate concentration required for a half-maximal rate and with about a 30% increase in maximum rate. Consequently, the hormone caused a substantial (2--4-fold) stimulation when any one of the above substrates was present at a near physiological concentration, but brought about only a relatively small stimulation (1.4-fold) when very high substrate concentrations were used. Provision of cytoplasmic reducing equivalents (by ethanol addition), or of precursor for acetyl-coenzyme A formation (by acetate addition)-stimulated incorporation of labeled alanine into glucose and their effects were additive with that of glucagon. This suggested that provision of either of these intermediates was not a means by which the hormone increased the incorporation of labeled substrate into glucose. NH4+ stimulated the incorporation of 20 mM [U-14C] lactate into glucose 2-fold, probably by promoting glutamate synthesis and thus enhancing the transamination of oxaloacetate to aspartate. Evidence was obtained to support the view that glucagon also increases glutamate production (presumably from endogenous protein). However, the stimulation of incorporation into glucose from 20 mM [U-14C] lactate by NH4+ plus glucagon was synergistic. This suggested that glucagon also stimulated the incorporation of labeled substrate into glucose by additional means. Stimulation of the incorporation of [U-14C] alanine into glucose by beta-hydroxybutyrate plus glucagon was also synergistic. This suggested that another action of glucagon may be to provide more intramitochondrial reducing potential.