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1. Leucine and its 2-oxo analogue, 4-methyl-2-oxopentanoate, increased the release of acetoacetate and 3-hydroxybutyrate from hemidiaphragms isolated from 40 h-starved rats. Glucose and lactate+pyruvate decreased basal and leucine-stimulated rates of ketone body production. 2. The production of acetoacetate + 3-hydroxybutyrate in response to addition of leucine was suppressed in hemidiaphragms from fed rats. 3. At 3 mM leucine, for each mumol of leucine oxidized in the branched-chain 2-oxo acid dehydrogenase reaction (measured as 14CO2 production from [1-14C]leucine), 0.84 mumol of acetoacetate + 3-hydroxybutyrate were produced. This stoichiometry may imply that acetoacetate derived from the partial oxidation of leucine is not further oxidized in situ. The physiological significance of these findings is discussed.

Chronic ethanol feeding in the rat is associated with a skeletal myopathy involving primarily type-II muscle fibres, which is recognised to be mediated via a specific impairment in protein turnover. This paper investigates whether the cause of this myopathy may be related to abnormalities in carbohydrate and lipid metabolism in different muscles. [U-14C]Glucose metabolism was examined in two muscles with different fibre compositions, the extensor digitorum longus (EDL) muscle, which contains predominantly type-II muscle fibres, and the soleus muscle, which is composed primarily of type-I muscle fibres. Feeding on the ethanol-supplemented Lieber-DeCarli liquid diet for 2 or 6 weeks was associated with profound disturbances in glucose metabolism in both EDL and soleus muscles, particularly in relation to rates of glycogen and alanine formation. We discuss the importance of these metabolic changes in relation to the genesis of chronic alcoholic skeletal myopathy.

The pattern of glycogen deposition in individual cardiothoracic and skeletal muscles in response to oral and intraperitoneal glucose administration was examined in 40 h-starved rats. Rates of glycogen synthesis were consistently higher in oxidative muscles than in non-oxidative muscles. Intragastric ethanol administration was associated with an impaired glycaemic response and the almost total abolition of glycogen deposition in oxidative muscles in response to oral or intraperitoneal glucose re-feeding. This effect was dose-dependent and differential, in that ethanol produced no equivalent impairment in glycogen deposition in non-oxidative muscles. Ethanol treatment also selectively promoted glycogenolysis in oxidative muscles in the starved state. There was positive correlation (P < 0.001) between the decrease in glycogen levels in soleus and diaphragm muscles in response to increasing ethanol doses and blood glucose and lactate concentrations after intraperitoneal glucose administration, implying that the basis for the impairment in glycogen synthesis may be diminished glucose availability. The mechanism whereby ethanol may differentially compromise carbohydrate metabolism in oxidative muscles is discussed.

Flux via the polyol pathway, which comprises the enzymes aldose reductase (AR) and sorbitol dehydrogenase (SDH), has been implicated in the debilitating complications of diabetes. Previous studies in this laboratory have indicated that erythrocyte AR activities are increased (by 72%) in insulin-dependent diabetic patients. To investigate the mechanism underlying this activation, the response of AR activity to oral glucose challenge was investigated in eight overnight-fasted human volunteers. Glucose consumption led to a transient activation (by 76%: P less than 0.01) of erythrocyte AR, which paralleled the rise and subsequent fall in blood glucose concentrations. It is concluded that erythrocyte AR activity is acutely modulated in response to hyperglycaemia by an as yet unknown mechanism.

The levels of DNA polymerase alpha, DNA polymerase delta, and its accessory protein, proliferating cell nuclear antigen (PCNA) were examined in the regenerating rat liver. The levels of DNA polymerase alpha and delta activities in regenerating liver extracts were determined by the use of the DNA polymerase alpha specific inhibitor, BuAdATP [2-(p-n-butylanilino)-9-(2-deoxy-beta-D-ribofuranosyl) adenine 5'-triphosphate], and monoclonal antibodies. These reagents showed that the total DNA polymerase activities increased ca. 4-fold during regeneration and that the fraction of DNA polymerase delta activity at the peak was 40% of the total DNA polymerase activity. Immunoblots and inhibition studies using specific antibodies showed that DNA polymerase delta and epsilon and PCNA were concomitantly induced after partial hepatectomy. The levels of both DNA polymerase delta and epsilon and PCNA reached their maxima at 24-36 h post hepatectomy, i.e., at the same time that in vivo DNA synthesis reached its peak. Partial purification and characterization of DNA polymerases delta and epsilon from the regenerating rat liver were also performed. These observations suggest that the variation of DNA polymerase delta and epsilon and PCNA during liver regeneration is closely related to DNA synthesis and is consistent with their involvement in DNA replication.

The rat chondrosarcoma chondrocyte has the dual capacity to metabolize glucose (mainly via glycolysis) and glutamine (via an oxidative pathway). Glutamine metabolism, unlike that of glucose, is unable to sustain intracellular ATP concentrations. Glutamine consumption by the chondrosarcoma chondrocyte, however, is significantly in excess of its utilization as an amide-group donor in hexosamine synthesis, implying a novel and major role in cell metabolism.

In theory, the complete oxidation to CO2 of amino acids that are metabolized by conversion into tricarboxylic acid-cycle intermediates may proceed via their conversion into acetyl-CoA. The possible adrenergic modulation of this oxidative pathway was investigated in isolated hemidiaphragms from 40 h-starved rats. Adrenaline (5.5 microM), phenylephrine (0.49 mM) and dibutyryl cyclic AMP (10 microM) inhibited 14CO2 production from 3 mM-[U-14C]valine by 35%, 28% and 19% respectively. At the same time, these agents stimulated glycogen mobilization (measured as a decrease in glycogen content) and glycolysis (measured as lactate release). Adrenaline, phenylephrine and dibutyryl cyclic AMP did not inhibit 14CO2 production from 3 mM-[U-14C]aspartate or 3 mM-[U-14C]glutamate, although, as in the presence of valine, the agents stimulated glycogen mobilization and glycolysis. The rate of proteolysis (measured as tyrosine release in the presence of cycloheximide) was not changed by adrenaline. The data indicate that the adrenergic inhibition of 14CO2 production from [U-14C]valine was not a consequence of radiolabel dilution. Inhibition was apparently specific for branched-chain amino acid metabolism in that the adrenergic agonists also inhibited 14CO2 production from [1-14C]valine, [1-14C]leucine and [U-14C]isoleucine. Since 14CO2 production from the 1-14C-labelled substrates is a specific measure of decarboxylation in the reaction catalysed by the branched-chain 2-oxo acid dehydrogenase complex, it is at this site that the adrenergic agents are concluded to act.

L-Phenylalanine is an allosteric inhibitor of M1-type pyruvate kinase. Accordingly, the effects were studied of 20 mM phenylalanine on the metabolism of 5 mM [U-14C]glucose and 3 mM L-[U-14C]glutamate by isolated hemidiaphragms from starved rats. Phenylalanine inhibited lactate and 14CO2 production from both substrates and stimulated alanine release. It is concluded that pyruvate kinase may have a dual role in intermediary metabolism in skeletal muscle: the enzyme is a component of the lower glycolytic pathway and is implicated in a pathway of amino acid oxidation and alanine synthesis.

Evidence is presented in support of a pathway in skeletal muscle of glyconeogenesis (glycogen biosynthesis de novo) from L-glutamate and related amino acids involving the enzyme phosphoenolpyruvate carboxykinase (PEP CK). In the rat hemidiaphragm in vitro, not only did L-[U]-14C]glutamate exert a glycogen-sparing action, but 14C-label was incorporated into glycogen. The incorporation is thought not to be simply via label randomization and was decreased by factors that increased glycolysis or pyruvate oxidation. 3-Mercaptopicolinate and amino-oxyacetate, specific inhibitors of PEP CK and aminotransferase-type enzymes, respectively, decreased 14C-incorporation from L-[U-14C]glutamate into glycogen. No quantitative determination of apparent glyconeogenic flux was made, and it remains to be established whether glyconeogenesis via PEP CK and/or via PEP CK coupled with "malic' enzyme (or pyruvate carboxylase) is functionally important in skeletal muscle.

Branched-chain amino acid metabolism in skeletal muscle promotes the production of alanine, an important precursor in hepatic gluconeogenesis. There is controversy concerning the origin of the carbon skeleton of alanine produced in muscle, specifically whether it is derived from carbohydrate via glycolysis (the glucose-alanine cycle) or from amino acid precursors (viz. glutamate, valine, isoleucine, methionine, aspartate, asparagine) via a pathway involving phosphoenolpyruvate (PEP) carboxykinase and pyruvate kinase, or NADP-malate dehydrogenase (malic enzyme). The relevant literature is reviewed and it is concluded that neogenic flux from amino acids is unlikely to be of major quantitative importance for provision of the carbon skeleton of alanine either in vitro or in vivo. Evidence is presented that branched-chain amino acid oxidation in muscle is incomplete and that the branched-chain 2-oxo acids and the products of their partial oxidation (including glutamine) are released. The role of these metabolites is discussed in the context of fuel homeostasis in starvation.

In mice, the response of carcass glycogen to glucose re-feeding after starvation is biphasic. The initial repletive phase is followed by partial (greater than 50%) glycogen mobilization. This turnover of carcass glycogen in response to carbohydrate re-feeding may play an important role in the provision of C3 precursors for hepatic glycogen synthesis.

Intravenous infusion of inosine (15 mg.kg-1.min-1) to the open-chested pig resulted in hypotension, coronary vasodilatation and slightly increased myocardial contractility. Following coronary occlusion, the action of inosine to increase myocardial contractility was apparently selective. Regional myocardial performance of ischaemic myocardium was increased significantly relative to nonischaemic. The selectivity of inotropic action was not mimicked by glucose-insulin-potassium. It is concluded that the selectivity is multifactoral and that the inotropic, vasodilatory and metabolic actions of the nucleoside contribute to the apparent selectivity.

1. The effects of intragastric glucose feeding and L-tri-iodothyronine (T3) administration on rates of hepatic and brown-fat lipogenesis in vivo were examined in fed and 48 h-starved rats. 2. T3 treatment increased hepatic lipogenesis in the fed but not the starved animals. Brown-fat lipogenesis was unaffected or slightly decreased by T3 treatment of fed or starved rats. 3. Intragastric glucose feeding increased hepatic lipogenesis in control or T3-treated fed rats, but did not increase hepatic lipogenesis in starved control rats. Glucose feeding increased hepatic lipogenesis if the starved rats were treated with T3. Glucose feeding increased rates of brown-fat lipogenesis in all experimental groups. The effects of glucose feeding on liver and brown-fat lipogenesis were mimicked by insulin injection. 4. The increase in hepatic lipogenesis in T3-treated 48 h-starved rats after intragastric glucose feeding was prevented by short-term insulin deficiency, but not by (-)-hydroxycitrate, an inhibitor of ATP citrate lyase. The increase in lipogenesis in brown adipose tissue in response to glucose feeding was inhibited by both short-term insulin deficiency and (-)-hydroxycitrate. 5. The results tend to preclude pyruvate kinase and acetyl-CoA carboxylase as the sites of interaction of insulin and T3 in the regulation of hepatic lipogenesis in 48 h-starved rats. Other potential sites of interaction are discussed.

3-Mercaptopicolinate (3-MPA) is a specific inhibitor of phosphoenolpyruvate carboxykinase (PEP CK). In vivo the hypoglycaemic action of 3-MPA in 24 h-starved rats was abolished on intragastric glucose refeeding. Nonetheless, 3-MPA decreased hepatic glycogen content and rate of synthesis in starved animals re-fed glucose. The inference is that on re-feeding after starvation hepatic glycogen is synthesised mainly de novo via glyconeogenesis involving PEP CK. 3-MPA increased hepatic lipogenesis in water- and glucose-fed normal and diabetic rats. This increase is presumed to result from inhibition of PEP CK and consequent diversion of pyruvate from gluconeogenesis to lipogenesis. In contrast, 3-MPA inhibited brown-fat lipogenesis in water- and glucose-fed rats.

Amylomaltase, the inducible 4-alpha-glucanotransferase of Escherichia coli strain ML, has been purified to homogeneity. Its specific activity with a commercial maltose substrate was 500 mkat/kg protein (30 mumol glucose formed min-1 mg protein-1). The purified enzyme, dependent on buffer concentration, exists in interconvertible low-molecular-weight (apparent molecular weight 71000) and high-molecular-weight (apparent molecular weight 370000) forms. The specificity of amylomaltase has been redefined. Hitherto, the enzyme was thought to be a glucosyltransferase, catalysing the transfer of single glucosyl units, and maltose has been regarded as its most important substrate. Amylomaltase is now shown to exhibit both glucosyl-transfer and 4-alpha-glucanosyl-transfer specificity. 4-alpha-Glucanosyl chains containing up to at least nine glucosyl units can be transferred. However, it is concluded that the transfer reaction by which amylomaltase action was originally expressed, does not take place, i.e., Maltose + maltose in equilibrium Maltotriose + glucose and that maltose has a restricted role as a substrate. This may be due to the inability of maltose to function as a donor substrate, serving only as an acceptor substrate. It is confirmed that when a maltodextrin serves as a donor, that portion of the molecule transfered by the enzyme is that containing the nonreducing-end-group. Enzyme action on chromatographically pure maltose is characterized by a lag phase in the time course of glucose release. The lag pahse is overcome by addition of 'priming' (catalytic) concentrations of maltotriose or higher maltodextrins. An autocatalytic reaction mechanism involving the generation of primer molecules is proposed to explain the action of the enzyme on maltose. The redefined action pattern of amylomaltase is consistent with the redefined role of the enzyme in the utilization of exogenous and endogenous 1,4-alpha-glucans by E. coli.

Proprietary naloxone hydrochloride (Narcan) acts on isolated hepatocytes from 24-h starved rats to increase 14CO2 production from [1-14C]oleate and to reverse in part the inhibitory effect of ethanol on the oxidation of [1-14C]oleate to 14CO2. The effects are attributable not to naloxone itself, but to the methyl p-hydroxybenzoate present in Narcan as a preservative. The question is posed as to whether methyl p-hydroxybenzoate and p-hydroxybenzoate contribute to the reported antagonism by proprietary naloxone of acute ethanol intoxication in vivo.

The allosteric inhibition of M1-type pyruvate kinase from rabbit skeletal muscle by phenylalanine is reciprocally dependent on Mg2+ and phosphoenolpyruvate concentrations. At pH 8, phenylalanine acts as a competitive inhibitor with respect to Mg2+ and phosphoenolpyruvate, and vice versa. Phenylalanine introduces sigmoidicity into the dependence of the reaction velocity on [Mg2+]. In vitro kinetic analysis indicates that phenylalanine inhibition of muscle pyruvate kinase is unlikely to have regulatory significance in vivo.

The vast majority of the adult population of most societies consume alcohol to some degree. In the U.K., although average alcohol consumption is moderate, it is not generally appreciated that the per capita consumption varies markedly within the population: approximately one-twentieth of the adult population accounts for half of the total alcohol consumed. Alcohol abuse is consequently a major health problem affecting 1-1.5 million people in this country. The most obvious effects of excessive alcohol consumption are on the central nervous system and on social behaviour. However, alcohol is metabolized predominantly in the liver and it can impair and impede the liver's capacity to metabolize other substances including nutrients, steroids, vitamins, and certain organic compounds foreign to the body (referred to as xenobiotics). It is possible therefore, from the biochemical perspective, to explain many of the effects of alcohol on the body on the basis of its interaction with essential liver metabolism. What remains obscure is the mechanism whereby chronic alcohol abuse leads to permanent damage to the liver and other organs. Recent research suggests that acetaldehyde (a metabolite of alcohol) may play a key role in this process.

There is mounting interest in the use of the monophasic action potential for electrophysiological investigation of regional myocardial ischaemia. There is, however, no systematic study of the relation between the changes in monophasic action potential and regional myocardial blood flow. In this study monophasic action potential and, for comparison, epicardial electrograms were recorded by suction electrode at 14 selected sites on the anterior surface of the normal left ventricle of the intact pig heart in situ (n = 16). The monophasic action potential duration varied across the left ventricle; it was shortest close to the left anterior descending coronary artery, increased laterally across the left ventricle, and was longer at the apex than at the base. This variation was independent of regional myocardial blood flow (measured with radiolabelled microspheres). After coronary occlusion, in nine of these pigs monophasic action potential duration significantly decreased in proportion to the reduction in regional myocardial blood flow. The ST segment of the epicardial electrogram was elevated in relation to the reduction in regional myocardial blood flow but correlated less well. The reduction in regional myocardial blood flow of approximately 50% produced maximal ST elevation. The monophasic action potential could be recorded from some sites within the border zone for up to 5 h but could not be recorded from the centre of an ischaemic zone. With ischaemic episodes of this duration there was, however, a return to baseline of the elevated ST segment for all sites within the compromised region. Monophasic action potential duration, unlike epicardial electrogram ST elevation, discriminates between central ischaemic and non-ischaemic and ischaemic sites on either side of the zone with a reduced blood flow. The results suggest that monophasic action potential duration measured by suction electrode may be a simple and reliable index of transmural-epicardial myocardial ischaemia in experimental studies and in surgery.

1 The pressor responses to injected noradrenaline (NA) of isolated perfused femoral or renal arteries of the rabbit were studied.2 Vascular smooth muscle is relatively resistant to hypoxia. A combination of hypoxia and dinitrophenol (DNP) respiratory uncoupling was necessary to abolish the pressor response to NA. Loss of the pressor response was assumed to result from decreased capacity of arteries to form adenosine 5'-triphosphate (ATP). Reperfusion of the hypoxic arteries with oxygenated medium resulted in recovery of the pressor response to NA.3 Inclusion of inosine (10 mM) in the hypoxic perfusion medium increased significantly the rate and extent of post-hypoxic recovery of the pressor response to NA.4 Whereas the presence of inosine in the hypoxic perfusion medium aided post-hypoxic recovery, inosine had no direct action on the pressor dose response to NA. Therefore, the action of inosine was protective as opposed to direct.5 The protective action of inosine did not involve potentiation of NA binding to NA-adrenoceptor sites (the equilibrium coefficient, K(eq) for NA-receptor interaction was unaltered by hypoxia and/or inosine).6 The results are discussed in terms of a presumptive mechanism whereby inosine is believed to act by maintaining intracellular adenine nucleotide concentrations in hypoxia.

In this study we utilized the phosphorylase b kinase-deficient (gsd/gsd) rat as a model of hepatic substrate utilization where there is a constraint on glycogenesis imposed by the maintenance of high glycogen concentrations. Glucose re-feeding of 48 h-starved gsd/gsd rats led to suppression of hepatic glucose output. In contrast with the situation in normal rats, activation of the pyruvate dehydrogenase complex and lipogenesis was observed. It is suggested that impeding glycogenic flux may divert substrate into lipogenesis, possibly via activation of the pyruvate dehydrogenase complex.

Branched-chain amino acid metabolism in hemidiaphragms from 40 h-starved rats is influenced by the provision of glucose as co-substrate. Glucose inhibits 14CO2 production from [l-14C]valine and [U-14C]valine but stimulates 14CO2 production from [l-14C]leucine, [U-14C]leucine and [U-14C]isoleucine. In the presence of glucose, ketone bodies inhibit alanine release and 14CO2 production from [l-14C]valine, [l-14C]leucine and [U-14C]isoleucine, but inhibition is not observed in the absence of glucose as cosubstrate. Glucose-dependent inhibition by ketone bodies of branched-chain amino acid oxidation via inhibition of the branched-chain 2-oxo acid dehydrogenase complex or branched-chain amino acid aminotransferase may account in part for the reported hypoalanaemic action of ketone bodies in vivo.

Dichloroacetate (an activator of pyruvate dehydrogenase) stimulates 14CO2 production from [U-14C]glucose, but not from [U-14C]glutamate, [U-14C]aspartate, [U-14C]- and [1-14C]-valine and [U-14C]- and [1-14C]-leucine. It is concluded (1) that pyruvate dehydrogenase is not rate-limiting in the oxidation to CO2 of amino acids that are metabolized to tricarboxylic acid-cycle intermediates, and (2) that carbohydrate (and not amino acids) is the main carbon precursor in alanine formation in muscle.

The effects of proline on lipogenesis in isolated rat hepatocytes were determined and compared with those of lactate, an established lipogenic precursor. Proline or lactate plus pyruvate increased lipogenesis (measured with 3H2O) in hepatocytes from fed rats depleted of glycogen in vitro and in hepatocytes from starved rats. Lactate plus pyruvate but not proline increased lipogenesis in hepatocytes from starved rats. ( - )-Hydroxycitrate, an inhibitor of ATP-citrate lyase, partially inhibited incorporation into saponifiable fatty acid of 3H from 3H2O and 14C from [U-14C]lactate with hepatocytes from fed rats. Incorporation of 14C from [U-14C]proline was completely inhibited. Similar complete inhibition of incorporation of 14C from [U-14C]proline by ( - )-hydroxycitrate was observed with glycogen-depleted hepatocytes or hepatocytes from starved rats. Inhibition of phosphoenolpyruvate carboxykinase by 3-mercaptopicolinate did not inhibit the incorporation into saponifiable fatty acid of 3H from 3H2O or 14C from [U-14C]proline or [U-14C]lactate. Both 3-mercaptopicolinate and ( - )-hydroxycitrate increased lipogenesis (measured with 3H2O) in the absence or presence of lactate or proline with hepatocytes from starved rats. The results are discussed with reference to the roles of phosphoenolpyruvate carboxykinase, mitochondrial citrate efflux, ATP-citrate lyase and acetyl-CoA carboxylase in proline- or lactate-stimulated lipogenesis.

The metabolism of odd-chain fatty acids was investigated in hepatocytes from 24 h-starved rats. Rates of glucose and 14CO2 production from [1-14C]propionate, [1-14C]valerate and [1-14C]nonanoate were maximal at 0.1 mM. Glucose production was greater with propionate as substrate than with valerate or nonanoate. Ketone body, lactate and pyruvate release were not affected by addition of the odd carbon fatty acids. It is concluded that hepatic odd-chain fatty acid metabolism in starvation is partly oxidative and partly gluconeogenic. Vasopressin and angiotensin II stimulated 14CO2 production from [1-14C] valerate and [1-14C]nonanoate but not from [1-14C]propionate and [1-14C]oleate in hepatocytes from starved rats. Nonanoate and valerate generate acetyl-CoA and propionyl-CoA, whereas oleate or propionate produce acetyl CoA and propionyl-CoA respectively. Given this stoichiometry, it is inferred that in hepatocytes from starved rats there must be an input of a tricarboxylic acid cycle intermediate to permit expression of the hormonal sensitivity.

This paper explores the mechanism(s) whereby liposomes accumulate in chronically ischaemic myocardium and intestine. Plasma prepared from venous blood obtained at sites of myocardial and intestinal infarction does not promote the lysis of positively and negatively charged liposomes in vitro. Albumin-bound lysophosphatidylcholine (greater than or equal to 2 mM) lyses positively and negatively charged liposomes in vitro at similar rates. [99mTc]Diethylenetriamine pentaacetic acid (DTPA) entrapped in positively charged liposomes was accumulated in ischaemic rat caecum/colon 6 and 24 h after mesenteric ligation. Presumably allied to the accumulation of liposomal components, necrotic caecum/colon showed marked Ca2+ accumulation and phospholipid depletion. It is postulated that Ca2+ and Ca2+-activated membrane phospholipases may be implicated in the mechanism of liposome accumulation in chronic ischaemia.

The purpose of this study was to establish whether liposomes administered via the intravenous route promote granulocyte aggregation and pulmonary leukostasis. White cells (labelled with [111In]tropolanate) and positively and negatively charged liposomes (containing entrapped [99mTc]DTPA) were administered i.v. to rats. The blood clearance and tissue distribution of 111In label was not altered by the administration of liposomes (and vice versa) and it is inferred that on intravenous liposome administration liposome/white-cell interactions are unlikely to compromise lung function.

3-Mercaptopicolinic acid (3-MPA) is reportedly a specific inhibitor of phosphoenolpyruvate (PEP) carboxykinase and has hitherto been used accordingly to elucidate the metabolic role of PEP carboxykinase in vitro and in vivo. We show that 3-MPA has multiple effects on intermediary metabolism in hemidiaphragms from 40 h-starved rats. It decreases the release of lactate + pyruvate and alanine in hemidiaphragms provided with no added substrate or with valine, leucine or isoleucine. Moreover, irrespective of the substrate provided (none, valine, leucine, isoleucine, glucose, acetate, oleate), 3-MPA decreases the [lactate]/[pyruvate] ratio. 3-MPA is without effect on 14CO2 production from [U-14C]valine, [1-14C]valine, [1-14C]leucine, [U-14C]isoleucine or [1-14C]oleate, but stimulates 14CO2 production from [U-14C]glucose and [1-14C]pyruvate and inhibits 14CO2 production from [1-14C]acetate. Glycolytic flux (measured as 3H2O formation from [5-3H]glucose) is stimulated by 3-MPA. It is concluded that 3-MPA has site(s) of actions other than PEP carboxykinase and that the putative role of PEP carboxykinase in alanine synthesis de novo in skeletal muscle from tricarboxylic acid-cycle intermediates and related amino acids requires reappraisal.

Effects of administration of tri-iodothyronine (T3) on activities of cardiac and renal pyruvate dehydrogenase complex (active form, PDHa) were investigated. In fed rats, T3 treatment did not affect cardiac or renal PDHa activity, although blood non-esterified fatty acid and ketone-body concentrations were increased. Starvation (48 h) of both control and T3-treated rats resulted in similar increases in the steady-state concentrations of fatty acids and ketone bodies, but inactivation of cardiac and renal pyruvate dehydrogenase complex activities was diminished by T3 treatment. Inhibition of lipolysis increased renal and cardiac PDHa in control but not in T3-treated 48 h-starved rats, despite decreased fatty acid and ketone-body concentrations in both groups. The results suggest that hyperthyroidism influences the response of cardiac and renal PDHa activities to starvation through changes in the metabolism of lipid fuels in these tissues.

14CO2 production from [l-14C]oleate, [l-14C]butyrate and [U-14C]proline by isolated rat hepatocytes was studied. In hepatocytes from fed rats, fatty acid and proline oxidation are stimulated in parallel by adrenaline, noradrenaline, vasopressin and angiotensin II. In contrast in hepatocytes from 24 h-starved rats these hormones stimulate proline oxidation whereas oleate and butyrate oxidation is hormone-insensitive. This suggests that 14CO2 production from [U-14C]proline and [l-14C]oleate is subject to independent endocrine control. In support of this in hepatocytes from fed rats, glucagon and dibutyryl cyclic AMP stimulate 14CO2 production from proline but inhibit 14CO2 production from [l-14C]oleate. The pathway of hepatic proline oxidation is discussed and it is suggested that 2-oxoglutarate dehydrogenase is one site of endocrine control of proline oxidation.

Rat lymphocytes incubated under hypoxic conditions in vitro show a time-dependent release of intracellular enzymes. As reported previously, enzyme release (lactate dehydrogenase) is decreased by metabolite, notably ATP and glucose, that contribute towards lymphocyte energy metabolism. The action of purine nucleosides in relation to enzyme release was investigated. Inosine was shown to decrease significantly lactate dehydrogenase release, whereas adenosine exerted a supportive action only at concentrations less than 0.5 mmol/l. Inosine decreased enzyme efflux maximally at concentrations of at least 2--3 mmol/l. The mechanism of inosine action was deduced to be primarily ribose 5-phosphate formation and its subsequent metabolism by energy-yielding pathways. Inosine was presumed also to enter the purine 'salvage pathway' and thereby maintain intracellular adenine nucleotide pools.

Partial intestinal ischaemia was produced by ligation of selected primary laterals of the mesenteric artery in the rat. Both positively and negatively charged liposomes (multiply labelled with [99mTc]diethylenetriamine pentaacetic acid, [3H]methoxy-inulin, and [4-14C]-cholesterol), administered 24 h following ligation, were accumulated in ischemic (necrotic) intestine.

The in vivo effects of dexamethasone administration on liver and extrahepatic tissue carnitine concentrations were assessed in 48-h-starved rats. In heart and kidney, but not in liver, dexamethasone significantly increased total carnitine concentration. Acute (2.5 h) treatment with 2-tetradecylglycidate (TDG), a specific inhibitor of carnitine palmitoyl transferase 1, not only increased total hepatic carnitine concentrations, but also permitted an effect of dexamethasone (a further increase in hepatic carnitine concentration). The results are discussed in terms of acute (substrate-mediated) and chronic (hormonal) control of carnitine turnover.

Multiply-labelled neutral or positively-charged liposomes were given iv to open-chested dogs or pigs 0.5 h or 5 h after coronary artery occlusion. Myocardial blood flow was measured by labelled microspheres. Animals were killed 3.5 h or 6 h after coronary artery occlusion and the myocardial distribution of liposomal labels was correlated with that of the microspheres. No evidence was found that liposomes are taken up preferentially by ischaemic myocardium. The results suggest that liposomes have limited potential as a means of drug delivery in myocardial infarction.

1. Intragastric administration of ethanol (75 mmol/kg body wt.) at 1 h before glucose refeeding of 24 h-starved rats inhibited hepatic glycogen deposition (by 69%) and synthesis (by approx. 70%), but was without significant effect on muscle glycogen deposition and synthesis. 2. Treatment of ethanol-administered rats with methylpyrazole (an inhibitor of alcohol dehydrogenase) did not significantly diminish the inhibitory effect of ethanol on hepatic glycogen deposition after glucose refeeding, suggesting that the inhibition was not dependent on ethanol metabolism. 3. Ethanol delayed and diminished intestinal glucose absorption, at least in part by delaying gastric emptying. 4. At a lower dose (10 mmol/kg body wt.), ethanol inhibited hepatic glycogen repletion and synthesis without compromising intestinal glucose absorption. Ethanol inhibited glycogen deposition (by 40%) in hepatocytes from starved rats provided with glucose + lactate + pyruvate as substrates, consistent with it having a direct effect to diminish hepatic glycogen synthesis by inhibition of gluconeogenic flux at a site(s) between phosphoenolpyruvate and triose phosphate in the pathway. 5. It is concluded that ethanol acutely impairs hepatic glycogen repletion by inhibition at at least two distinct sites, namely (a) intestinal glucose absorption and (b) hepatic gluconeogenic flux.

Liposomes accumulate is ischaemic rat intestine 24 h after mesenteric occlusion. The accumulation of liposomal components is shown to depend on necrotic or allied alterations in cell integrity/function associated with chronic ischaemia. Moreover, not all liposomal components accumulate at sites of infarction. It is concluded therefore that liposomes are likely to be of little value in the diagnosis and management of ischaemic disorders.

Renal failure is associated with peripheral insulin resistance and consequent carbohydrate intolerance. This report investigates carbohydrate metabolism in vitro in epitrochlearis and hemidiaphragm muscles taken from acutely uraemic and sham-operated rats. Muscles from acutely uraemic rats (compared to those from sham-operated rats) incubated with 5 mM glucose showed increased rates of basal and insulin-stimulated glycolysis and glycogen turnover, but pyruvate dehydrogenase and tricarboxylic acid-cycle flux was not increased in uraemia. Glycolysis (but not glycogen turnover) in muscles from acutely uraemic rats tended to show decreased responsiveness to stimulation by insulin. It is concluded that acute uraemia is associated with a defect(s) in muscle that produces intrinsic insulin resistance and results in diversion of glucose (both in basal and insulin-stimulated states) from glycogen synthesis into glycolysis.

Vasopressin and angiotensin II inhibited lipogenesis (measured with 3H2O) in hepatocytes from fed rats. Inhibition was also observed with hepatocytes from fed rats which had been depleted of glycogen in vitro and incubated with lactate + pyruvate (5 mM + 0.5 mM) as substrates. The inhibitory actions of the hormones are therefore independent of hormone-mediated changes in glycogenolytic or glycolytic flux from glycogen, and thus the site(s) of hormone action must be subsequent to the formation of lactate. (-)Hydroxycitrate, a specific inhibitor of ATP-citrate lyase, decreased lipogenesis in hepatocytes from fed rats incubated with lactate + pyruvate by approx. 51% but had little effect on lipogenesis in glycogen-depleted hepatocytes similarly incubated. There was parallel inhibition of incorporation of 14C from [U-14C]lactate into fatty acid and lipogenesis as measured with 3H2O in each case. Thus depletion of glycogen, or conceivably the process of glycogen-depletion (incubation with dibutyryl cyclic AMP) causes a change in the rate-determining step(s) for lipogenesis from lactate. Vasopressin and angiotensin II also decreased lipogenesis and incorporation of 14C into fatty acids in glycogen-depleted hepatocytes provided with [U-14C]proline as opposed to [U-14C]-lactate. However, proline-stimulated lipogenesis was inhibited by (-)hydroxycitrate, and proline-stimulated lipogenesis and incorporation of 14C from [U-14C]-proline were not decreased in parallel by this inhibitor (inhibition of 52% and 85% respectively). It is inferred that lactate and proline stimulate lipogenesis by different mechanisms and incorporation of 14C from [U-14C]proline and [U-14C]lactate into fatty acid occurs via different routes.(ABSTRACT TRUNCATED AT 250 WORDS)