Gluconeogenesis from acetone in starved rats.

To non-anaesthetized rats starved for 3 days, [U-14C]acetone, NaH14CO3, L-[U-14C]lactate, [2-14C]acetate or D-[U-14C]- plus D-[3-3H]-glucose was injected intravenously. From the change in the plasma concentration of labelled acetone versus time after the injection, the metabolic clearance rate of acetone was calculated as 2.25 ml/min per kg body wt., and its rate of turnover as 0.74 mumol/min per kg. The extent and time course of the labelling of plasma glucose, lactate, urea and acetoacetate were followed and compared with those observed after the injection of labelled lactate, acetate and NaHCO3. The labelling of plasma lactate was rapid and extensive. Some 1.37% of the 14C atoms of circulating glucose originated from plasma acetone, compared with 44% originating from lactate. By deconvolution of the Unit Impulse Response Function of glucose, it was shown that the flux of C atoms from acetone to glucose reached a peak at about 100 min after injection of labelled acetone. In comparable experiments the transfer from lactate reached a peak at 14 min after the injection of labelled lactate. It was concluded that acetone is converted into lactate to a degree sufficient to account for the labelling of plasma glucose and is thus a true, albeit minor, substrate of glucose synthesis in starved rats.     

The stimulation of tricarboxylic acid-cycle flux by alpha-adrenergic agonists in perfused rat liver.

Output of 14CO2 from 1-14C-labelled glutamate, 2-oxoglutarate or octanoate and from 4-methyl-2-oxo[2-14C]pentanoate was increased by more than 100% after infusion of phenylephrine into perfused livers of fed rats. Infusion of ethanol or sorbitol raised 3-hydroxybutyrate/acetoacetate ratios and decreased the output of 14CO2. Increases in 14CO2 output induced by phenylephrine were observed in the presence or absence of ethanol or sorbitol and were accompanied by elevated 3-hydroxybutyrate/acetoacetate ratios under all conditions examined. Phenylephrine had no effect on total tissue ATP/ADP ratios in livers from fed or starved rats. The data suggest that phenylephrine-induced increases in tricarboxylic acid-cycle flux do not arise from lowered matrix NADH/NAD+ or ATP/ADP ratios.     

Inhibition of hepatic proteolysis by insulin. Role of hormone-induced alterations of the cellular K+ balance

1. Proteolysis was measured as [3H]leucine release from isolated perfused livers from rats, which had been labeled in vivo by an intraperitoneal injection of [3H]leucine about 16 h prior to the perfusion experiment. In livers from fed rats, insulin (35 nM) inhibited [3H]leucine release by 24.5 +/- 1.3% (n = 15) and led to an amiloride-sensitive, bumetanide-sensitive and furosemide-sensitive net K+ uptake of 5.53 +/- 0.31 mumol.g-1 (n = 15). Both the insulin effects on net K+ uptake and on [3H]leucine release were diminished by about 65% or 55% in presence of furosemide (0.1 mM) or bumetanide (5 microM), respectively. The insulin-induced net K+ uptake was virtually abolished in the presence of amiloride (1 mM) plus furosemide (0.1 mM). 2. In perfused livers from 24-h-starved rats, both the insulin-stimulated net K+ uptake and the insulin-induced inhibition of [3H]leucine release were about 80% lower than observed in experiments with livers from fed rats. The insulin effects on K+ balance and [3H]leucine release were not significantly influenced in the presence of glycine (2 mM), although glycine itself inhibited [3H]leucine release by 30.3 +/- 0.3% (n = 4) and 13.8 +/- 1.2% (n = 5) in livers from starved and fed rats, respectively. When livers from fed rats were preswollen by hypoosmotic perfusion (225 mOsmol.l-1), both the insulin-induced net K+ uptake and the inhibition of [3H]leucine release were diminished by 50-60%. 3. During inhibition of [3H]leucine release by insulin, further addition of glucagon (100 nM) led to a marked net K+ release from the liver (3.82 +/- 0.24 mumol.g-1), which was accompanied by stimulation of [3H]leucine release by 16.4 +/- 4.6% (n = 4). 4. Ba2+ (1 mM) infusion led to a net K+ uptake by the liver of 3.2 +/- 0.2 mumol.g-1 (n = 4) and simultaneously inhibited [3H]leucine release by 12.4 +/- 1.7% (n = 4). 5. There was a close relationship between the Ba2+ or insulin-induced net K+ uptake and the degree of inhibition of [3H]leucine release, even when the K+ response to insulin was modulated by bumetanide, furosemide, glucagon, hypotonic or glycine-induced cell swelling or the nutritional state. 6. The data suggest that the insulin-induced net K+ uptake involves activation of both NaCl/KCl cotransport and Na+/H+ exchange.(ABSTRACT TRUNCATED AT 400 WORDS)     

Hormonal regulation of the tricarboxylic acid cycle in the isolated perfused rat liver

The effect of Ca2+-mobilizing hormones, vasopressin, angiotensin II and the alpha-adrenergic agonist phenylephrine, on the metabolic flux through the tricarboxylic acid cycle was investigated in isolated perfused rat livers. All three Ca2+-mobilizing agonists stimulated 14CO2 production and gluconeogenesis in livers of 24-h-fasted rats perfused with [2-14C]pyruvate. Prazosin blocked the phenylephrine-elicited stimulation of 14CO2 and glucose production from [2-14C]pyruvate whereas the alpha 2-adrenergic agonist, BHT-933, did not affect the rates of 14CO2 and glucose production from [2-14C]pyruvate indicating that the phenylephrine-mediated response involved alpha 1-adrenergic receptors. Phenylephrine, vasopressin and angiotensin II stimulated 14CO2 production from [2-14C]acetate in livers derived from fed rats but not in livers of 24-h-fasted rats. In livers of 24-h-fasted rats, perfused with [2-14C]acetate, exogenously added pyruvate was required for an increase in the rate of 14CO2 production during phenylephrine infusion. This last observation suggests increased pyruvate carboxylation as one of the mechanisms involved in stimulation of tricarboxylic acid cycle activity by the Ca2+-mobilizing agonists, vasopressin, angiotensin II and phenylephrine.     

Pseudoketogenesis in the perfused rat heart

Ketogenesis is usually measured in vivo by dilution of tracers of (3R)-hydroxybutyrate or acetoacetate. We show that, in perfused working rat hearts, the specific activities of (3R)-hydroxybutyrate and acetoacetate are diluted by isotopic exchanges in the absence of net ketogenesis. We call this process pseudoketogenesis. When hearts are perfused with buffer containing 2.3 mM of [4-3H]- plus [3-14C]acetoacetate, the specific activities of [4-3H] and [3-14C]acetoacetate decrease while C-1 of acetoacetate becomes progressively labeled with 14C. This is explained by the reversibility of reactions catalyzed by mitochondrial 3-oxoacid-CoA transferase and acetoacetyl-CoA thiolase. After activation of labeled acetoacetate, the specific activity of acetoacetyl-CoA is diluted by unlabeled acetoacetyl-CoA derived from endogenous fatty acids or glucose. Acetoacetyl-CoA thiolase partially exchanges 14C between C-1 and C-3 of acetoacetyl-CoA. Finally, 3-oxoacid-CoA transferase liberates weakly labeled acetoacetate which dilutes the specific activity of extracellular acetoacetate. An isotopic exchange in the reverse direction is observed when hearts are perfused with unlabeled acetoacetate plus [1-14C]-, [13-14C]-, or [15-14C]palmitate; here also, acetoacetate becomes labeled on C-1 and C-3. Computations of specific activities of (3R)-hydroxybutyrate, acetoacetate, and acetyl-CoA yield minimal rates of pseudoketogenesis ranging from 19 to 32% of the net uptake of (3R)-hydroxybutyrate plus acetoacetate by the heart.     

Influence of ethanol on the liver metabolism of fed and starved rats

1. The influence of ethanol on the metabolism of livers from fed and starved rats has been studied in liver-perfusion experiments. Results have been obtained on oxygen consumption and carbon dioxide production, on glucose release and uptake by the liver and on changes in the concentrations of lactate and pyruvate and of β-hydroxybutyrate and acetoacetate in the perfusion medium. 2. Oxygen consumption and carbon dioxide production were lower in livers from starved rats than in livers from fed rats. Ethanol had no effect on the oxygen consumption of either type of liver. After the addition of ethanol to the perfusion medium carbon dioxide production ceased almost completely, the change being faster in livers from starved rats. 3. With livers from fed rats glucose was released from the liver into the perfusion medium. This release was slightly greater when ethanol was present. With livers from starved rats no release of glucose was observed, and when ethanol was added a marked uptake of glucose from the medium was found. A simultaneous release of glycolytic end products, lactate and pyruvate, into the medium occurred. 4. Acetate was the main metabolite accumulating in the perfusion medium when ethanol was oxidized. With livers from starved rats a slightly increased formation of ketone bodies was found when ethanol was present. 5. The lactate/pyruvate concentration ratio in the perfusion medium increased from 10 to 87 with livers from fed rats and from 20 to 171 with livers from starved rats when the livers were perfused with ethanol in the medium. The β-hydroxybutyrate/acetoacetate concentration ratio increased from 0·8 to 7·6 with livers from fed rats and from 1·0 to 9·5 with livers from starved rats when ethanol was added to the medium. 6. The effects of ethanol are discussed and related to changes in the redox state of the liver that produce new conditions for some metabolic pathways.     

Lacto-N-neotetraosylceramide ("paragloboside") as a possible tumor-associated surface antigen of hamster NILPY tumor.

Isolated rat hepatocytes from fed and starved rats synthesized net glucose from various precursors at similar rates. [3-¹⁴C]-lactate incorporation into glucose was also similar in hepatocytes from fed and starved rats, as was ketone body formation from oleate and octanoate. Rates of gluconeogenesis in hepatocytes from fed rats compare to rates seen in perfused livers from starved rats rather than perfused livers from fed rats. Thus metabolic rates and possibly controls may be different between perfused livers and isolated hepatocytes when using fed rats.     

Pathways of acetone's metabolism in the rat

Distributions of 14C were different from those of 13C in glucoses formed by livers of rats in diabetic ketosis and perfused with [2-14C]acetone and [2-13C]lactate. There was 32-73% of the 14C and 8-12% of the 13C in carbons 3 and 4 of the glucoses with the remaining 14C and 13C distributed about equally in the other carbons. Incorporations of 14C from [2-14C]acetone (14-39%) also exceeded those from [2-14C]pyruvate (8-10%) into carbons 3 and 4 of glucoses formed by hepatocytes from rats fed acetone or fasted. [2-14C]Acetone and [2-14C]pyruvate were infused into rats that were fed, fasted, given acetone in their drinking water, or in diabetic ketosis. Thirty-seven to 52% of the 14C in the glucoses formed was in their carbons 3 and 4 when the acetone was infused and 8 to 14% when the pyruvate was infused. [1,3-14C]Hydroxybutyrate was formed by the rats in diabetic ketosis given [2-14C]acetone. It is concluded that acetone is metabolized in rats to a large extent by a pathway in which lactate or its metabolic equivalent is not an intermediate and that pathway is via acetyl-CoA. via acetyl-CoA.     

Correction for metabolic exchange in the calculation of the rate of gluconeogenesis in rats

The degree by which the rate of gluconeogenesis is underestimated when calculated from the transfer of 14C atoms from circulating precursors to plasma glucose was estimated from the ratio of the specific activity of plasma glucose and blood acetoacetate during the infusion of [2-14C]acetate in rats fasted for 3 days. The specific activity of blood acetoacetate was taken to be equal to that of its only precursor, the acetyl C atoms of hepatocellular AcCoA. These latter are assumed not to be available for the net synthesis of glucose and may be incorporated into the molecule by "metabolic exchange" in the hepatic oxalo-acetate pool only. By this approach 25% of the C atoms of plasma glucose have been estimated to arise from AcCoA. Multiplication by a correction factor H = 1.33 +/- 0.03 is being suggested to compensate for the metabolic exchange of 14C for 12C atoms when the rate of gluconeogenesis is calculated from the transfer of 14C atoms from labeled precursors to glucose.     

Glucose phosphorylation is not rate limiting for accumulation of glycogen from glucose in perfused livers from fasted rats

Incorporation of Glc and Fru into glycogen was measured in perfused livers from 24-h fasted rats using [6-3H]Glc and [U-14C]Fru. For the initial 20 min, livers were perfused with low Glc (2 mM) to deplete hepatic glycogen and were perfused for the following 30 min with various combinations of Glc and Fru. With constant Fru (2 mM), increasing perfusate Glc increased the relative contribution of Glc carbons to glycogen (7.2 +/- 0.4, 34.9 +/- 2.8, and 59.1 +/- 2.7% at 2, 10, and 20 mM Glc, respectively; n = 5 for each). During perfusion with substrate levels seen during refeeding (10 mM Glc, 1.8 mumol/g/min gluconeogenic flux from 2 mM Fru), Fru provided 54.7 +/- 2.7% of the carbons for glycogen, while Glc provided only 34.9 +/- 2.8%, consistent with in vivo estimations. However, the estimated rate of Glc phosphorylation was at least 1.10 +/- 0.11 mumol/g/min, which exceeded by at least 4-fold the glycogen accumulation rate (0.28 +/- 0.04 mumol of glucose/g/min). The total rate of glucose 6-phosphate supply via Glc phosphorylation and gluconeogenesis (2.9 mumol/g/min) exceeded reported in vivo rates of glycogen accumulation during refeeding. Thus, in perfused livers of 24-h fasted rats there is an apparent redundancy in glucose 6-phosphate supply. These results suggest that the rate-limiting step for hepatic glycogen accumulation during refeeding is located between glucose 6-phosphate and glycogen, rather than at the step of Glc phosphorylation or in the gluconeogenic pathway.     

Determinants in the pathways followed by the carbons of acetone in their conversion to glucose

[2-14C]Acetone was infused into rats that were fed or fasted. Each was infused with either a trace quantity of acetone or a large quantity that resulted in a blood concentration of acetone of at least 4 mM. The distribution of 14C in the carbons of glucose from each rat was determined. Two of the rats were given acetone in their drinking water and one was diabetic. Whether a rat was chronically exposed to acetone, fed or fasted, normal or diabetic, if given the trace dose, over 80% of the 14C in the glucose it formed was in carbons 1, 2, 5, and 6 of the glucose. If a rat was given the large dose, about 50% was in carbons 3 and 4. Thus, the major determinant of the pathways followed by acetone when it is metabolized is its concentration and not the prior dietary state of the animal or its previous exposure to acetone. Incorporation into carbons 1, 2, 5, and 6 occurs in the conversion of the carbons of [2-14C]lactate into glucose, whereas incorporation into carbons 3 and 4 occurs in the conversion of the carbons of [1-14C]acetate into glucose. Therefore, at high acetone concentration, the pathway that has been proposed for acetone's metabolism via acetate predominates, and via acetate there can be no net synthesis of glucose from acetone. When rats were given cyanamide and then the large dose of acetone, 74% of the 14C in the glucose they formed was in carbons 3 and 4 of the glucoses. Thus, the relative contribution of the pathway to lactate, or its metabolic equivalent, that has been proposed appears to be lessened by the administration of an aldehyde dehydrogenase inhibitor.     

On the lack of formation of l-(+)-3-hydroxybutyrate by liver

The terminal carbon of palmitic acid, traced with ¹⁴C, is preferentially incorporated into carbon 4 of hydroxybutyrate formed by hepatocytes and perfused livers from 18- to 19-day-old rats and perfused livers from fasted adult rats. However, ¹⁴C from [13-¹⁴C]palmitic acid is incorporated into carbon 1 of the hydroxybutyrate to the same extent as any one of the first 12 carbons of palmitic acid as assessed with [1-¹⁴C]palmitic acid and [6-¹⁴C]palmitic acid. Therefore, the hydroxybutyrate is formed via hydroxymethylglutaryl-CoA, i.e., it is in the d configuration, and hydrolysis of l-hydroxybutyryl-CoA, the intermediate in the β oxidation of the palmitate, does not occur. Further, a negligible amount of ¹⁴C remains in hydroxybutyrate formed from ¹⁴C-labeled palmitic acid by isolated hepatocytes and perfused livers from the young rats, when the hydroxybutyrate is treated with d-(?)-3-hydroxybutyrate dehydrogenase to convert the d isomer to acetoacetate. Thus, l-(+)-3-hydroxybutyrate is not produced by rat liver as assessed using these preparations.     

Effect of fish oil diet on hepatic lipid metabolism in nonhuman primates: lowering of secretion of hepatic triglyceride but not apoB

African green monkeys were fed diets containing either 11% (by weight) fish oil or lard for 2.5 yr. To test the hypothesis that fish oil decreases hepatic secretion of triglyceride (TG) and apoB, livers from these animals were perfused with a fatty acid mixture [85% (w/w) oleate containing [14C]oleate and 15% n-3 containing [3H]eicosapentaenoic acid (EPA)] at a rate of 0.1 mumol fatty acid/min per g liver. Liver perfusate was sampled every 30 min during 4 h of recirculating perfusion. The concentration of triglyceride was similar for livers of animals of both groups and there was no difference between groups in the extent of incorporation of [3H]EPA or [14C]oleate into hepatic TG. While the secretion rate for the mass of TG was less in the fish oil-fed group (8.3 +/- 2.5 vs 18.3 +/- 4.4 mg/h per 100 g liver, P less than 0.05), the apoB secretion rate was similar (0.92 +/- 0.15 vs 1.01 +/- 0.13 mg/h per 100 g liver). Significantly less [3H]EPA was incorporated into secreted TG in the fish oil group (0.4 +/- 0.1 vs 1.0 +/- 0.1% infused dose/h; P less than 0.01). The rate of secretion of [14C]TG was similar for both groups (1.3 +/- 0.3 vs 1.4 +/- 0.1% infused dose/h for fish oil and lard groups, respectively). No significant diet-related differences in [3H]TG or [14C]TG fatty acid specific activity were observed for perfusate TG or hepatic TG. After perfusion, livers from fish oil-fed monkeys contained significantly more [3H]EPA in hepatic phospholipid than livers from lard-fed monkeys (19.5 +/- 1.8 vs 11.4 +/- 1.7% infused dose; P less than 0.01) although hepatic phospholipid mass concentrations were similar. The liver phospholipids of the fish oil group were enriched in n-3 fatty acid mass and were relatively depleted of oleate and linoleate. We conclude that although apoB secretion was unaffected, dietary fish oil significantly decreased hepatic TG secretion through relatively poor utilization of EPA for the synthesis of TG destined for secretion in VLDL; at the same time, increased incorporation of [3H]EPA into hepatic phospholipid accompanied the decreased incorporation into secreted TG and these events may be coupled.(ABSTRACT TRUNCATED AT 400 WORDS)     

Regulation of gluconeogenesis from pyruvate and lactate in the isolated perfused rat liver

The effects of glucagon and the alpha-adrenergic agonist, phenylephrine, on the rate of 14CO2 production and gluconeogenesis from [1-14C]lactate and [1-14C]pyruvate were investigated in isolated perfused livers of 24-h-fasted rats. Both glucagon and phenylephrine stimulated the rate of 14CO2 production from [1-14C]lactate but not from [1-14C]pyruvate. Neither glucagon nor phenylephrine affected the activation state of the pyruvate dehydrogenase complex in perfused livers derived from 24-h-fasted rats. 3-Mercaptopicolinate, an inhibitor of the phosphoenolpyruvate carboxykinase reaction, inhibited the rates of 14CO2 production and glucose production from [1-14C]lactate by 50% and 100%, respectively. Furthermore, 3-mercaptopicolinate blocked the glucagon- and phenylephrine-stimulated 14CO2 production from [1-14C]lactate. Additionally, measurements of the specific radioactivity of glucose synthesized from [1-14C]lactate, [1-14C]pyruvate and [2-14C]pyruvate indicated that the 14C-labeled carboxyl groups of oxaloacetate synthesized from 1-14C-labeled precursors were completely randomized and pyruvate----oxaloacetate----pyruvate substrate cycle activity was minimal. The present study also demonstrates that glucagon and phenylephrine stimulation of the rate of 14CO2 production from [1-14C]lactate is a result of increased metabolic flux through the phosphoenolpyruvate carboxykinase reaction, and phenylephrine-stimulated gluconeogenesis from pyruvate is regulated at step(s) between phosphoenolpyruvate and glucose.     

Rates of ketone-body formation in the perfused rat liver

1. The rates of formation of acetoacetate and β-hydroxybutyrate by the isolated perfused rat liver were measured under various conditions. 2. The rates found after addition of butyrate, octanoate, oleate and linoleate were about 100μmoles/hr./g. wet wt. in the liver of starved rats. These rates are much higher than those found with rat liver slices. 3. The differences between the rates given by slices and by the perfused organ were much higher with the long-chain than with short-chain fatty acids. The increments caused by oleate and linoleate were 12 and 16 times as large in the perfused organ as in the slices, whereas the increments caused by butyrate and octanoate were about four times as large. 4. The rates of ketogenesis in the unsupplemented perfused liver of well-fed rats, and the increments caused by the addition of fatty acids, were about half of those in the liver from starved rats. 5. The value of the [β-hydroxybutyrate]/[acetoacetate] ratio of the medium was raised by octanoate, oleate and linoleate. 6. Carnitine did not significantly accelerate ketogenesis from fatty acids. 7. Oleate formed up to 82% of the expected yield of ketone bodies. 8. In the liver of alloxan-diabetic rats the endogenous rates of ketogenesis were raised, in some cases as high as in the liver from starved rats, after addition of oleate. 9. On addition of either β-hydroxybutyrate or acetoacetate to the perfusion medium the liver gradually adjusted the [β-hydroxybutyrate]/[acetoacetate] ratio towards the normal range. 10. The [β-hydroxybutyrate]/[acetoacetate] ratio of the medium was about 0·4 when slices were incubated, but near the physiological value of 2 when the liver was perfused. 11. The experiments demonstrate that for the study of ketogenesis slices are in many ways grossly inferior to the perfused liver.     

Effects of pleural pressure and abdominal pressure on diaphragmatic blood flow

Alveolar transfer of prostaglandin E2 (PGE2) was characterized in isolated perfused guinea pig lungs (n = 19) by measuring radioactivity appearing in the venous effluent during 30 min after intratracheal instillation of [3H]PGE2, [14C]-mannitol, and [125I]iodoantipyrine. Recovery of lipid-soluble [125I]iodoantipyrine [91 +/- 3% (SE)] after 30 min was used to estimate total 3H and 14C delivered to the exchanging region of lung at time 0. In seven control lungs, 58 +/- 4% of [14C]mannitol and 16 +/- 4% of [3H]PGE2 was retained 10 min after instillation. Neither perfusion with diphloretin phosphate (10 micrograms/ml; n = 4) nor hypothermia (5 degrees C; n = 5) significantly affected the amount of [14C]mannitol retained; however, [3H]PGE2 remaining in these lungs increased significantly to 36 +/- 4 and 53 +/- 2%, respectively. Addition of unlabeled PGE2 (200 micrograms) to the instilled solution (n = 3) increased retention of both [14C]mannitol (80 +/- 3%) and [3H]PGE2 (65 +/- 4%). Alveolar transfer of [3H]PGE2 was calculated as the difference in percent retention of [14C]mannitol and [3H]PGE2 and normalized to that of [14C]mannitol. After 10 min, alveolar transfer of [3H]PGE2 was 71 +/- 8% in control lungs but was decreased to 26 +/- 7, 10 +/- 5, and 19 +/- 6% by diphloretin phosphate, hypothermia, or unlabeled PGE2, respectively. These data suggest that alveolar clearance of PGE2 involves a saturable drug- and temperature-sensitive process.     

Plasmodium berghei: gluconeogenesis in the infected mouse liver studied by 13C nuclear magnetic resonance

Using 13C nuclear magnetic resonance, we have compared the gluconeogenic activity of perfused livers isolated from normal starved mice and mice highly parasitized with Plasmodium berghei, using [2-13C]pyruvate as substrate. In both types of livers, 13C labeling of glucose carbons occurred in positions 1, 2, 5, and 6. The equal proportions of [1,6-13C]- and [2,5-13C]glucose in livers from malarial and normal mice suggests that pyruvate enters the gluconeogenic pathway directly and, to an equal extent, via the tricarboxylic acid cycle. The normalized signal heights indicated that at a given time after the addition of [2-13C]pyruvate the degree of 13C labeling in glucose carbons was reduced in livers from malarial animals, when compared to livers from normal animals. During the course of the perfusion experiment, the [2-13C]lactate resonance signal was always more intense from livers of malarial animals than from normal animals. A reduced activity of hepatic gluconeogenesis in malarial animals was further confirmed by a separate set of perfusion experiments which showed a 56% reduction of the measured rate of glucose production in livers from malarial animals, with respect to that of normal animals. A lowered NAD/NADH ratio in livers from malarial animals would explain the increased proportion of lactate observed in the spectra and be related to a decreased gluconeogenic rate. A more reduced oxidoreduction level in the hepatocytes of a malarial animal would result from a defect in the oxidative phosphorylation activity of mitochondria.     

Effect of ischaemic limb injury on the rates of metabolism of ketone bodies in starved rats.

1. Rats starved for 30h were injected with trace amounts of [3-14C]acetoacetate and beta-hydroxy[3-14C]butyrate 1h after ischaemic limb injury in a 20 degrees C environment, and the concentrations and radioactivities of blood ketone bodies were determined at intervals. 2. Starvation alone raised the rates of production and utilization of beta-hydroxybutyrate plus acetoacetate about 3.7-fold, but lowered their metabolic clearance rates by about 50%. In the starved rat ketone-body oxidation could account for up to 30% of whole body O2 consumption. 3. Injury in starved rats lowered the rates of production and utilization of both beta-hydroxybutyrate and acetoacetate, the combined fall of about 37% slightly exceeding the concomitant fall in whole-body O2 consumption. The concentration of beta-hydroxybutyrate decreased after injury, but its metabolic clearance rate was unaltered; the concentration of acetoacetate rose slightly and its metabolic clearance rate fell.     

Stimulation of [1-14C]oleate oxidation to 14CO2 in isolated rat hepatocytes by the catecholamines, vasopressin and angiotensin. A possible mechanism of action.

Adrenaline, noradrenaline, vasopressin and angiotensin increased 14CO2 production from [1-14C]oleate by hepatocytes from fed rats but not by hepatocytes from starved rats. The hormones did not increase 14CO2 production when hepatocytes from fed rats were depleted of glycogen in vitro. Increased 14CO2 production from ]1-14C]oleate in response to the hormones was observed when hepatocytes from starved rats were incubated with 3-mercaptopicolinate, an inhibitor of phosphoenolpyruvate carboxykinase. 3-Mercaptopicolinate inhibited uptake and esterification of [1-14C]oleate, slightly increased 14CO2 production from [1-14C]oleate and greatly increased the [3-hydroxybutyrate]/[acetoacetate] ratio. In the presence of 3-mercaptopicolinate 14CO2 production in response to the catecholamines was blocked by the alpha-antagonist phentolamine and required extracellular Ca2+. The effects of vasopressin and angiotensin were also Ca2+-dependent. The actions of the hormones of 14CO2 production from [I-14C]oleate by hepatocytes from starved rats in the presence of 3-mercaptopicolinate thus have the characteristics of the response to the hormones found with hepatocytes from fed rats incubated without 3-mercaptopicolinate. The stimulatory effects of the hormones on 14CO2 production from [1-14C]oleate were not the result of decreased esterification (as the hormones increased esterification) or increased beta-oxidation. It is suggested that the effect of the hormones to increase 14CO2 production from [1-14C]oleate are mediated by CA2+-activation of NAD+-linked isocitrate dehydrogenase, the 2-oxoglutarate dehydrogenase complex, and/or electron transport. The results also demonstrate that when the supply of oxaloacetate is limited it is utilized for gluconeogenesis rather than to maintain tricarboxylic acid-cycle flux.     

The site of cartilage matrix degradation.

1. The metabolism of VLD lipoproteins (very-low-density lipoproteins) was studied in intact isolated beating-heart cells and isolated perfused rat heart from starved animals by using [14C]triacylglycerol fatty acid-labelled VLD lipoprotein prepared from rats previously injected with [1-14C]palmitate. 2. 14C-labelled VLD lipoprotein was metabolized by the isolated perfused heart, but was only minimally metabolized by the heart cells unless an exogenous source of lipoprotein lipase was added. 3. Measurements of lipoprotein lipase at pH 7.4 with the natural substrate 14C-labelled VLD lipoprotein indicated that during collagenase perfusion of the heart the enzyme was released into the perfusate, the activity released being proportional to the concentration of collagenase used. Lipoprotein lipase activity in homogenates of hearts that had been perfused with collagenase showed a corresponding loss of activity. 4. At high perfusate concentrations of collagenase, inactivation of the released lipoprotein lipase occurred. 5. Lipoprotein lipase activity was largely undetectable in the homogenate of the isolated heart cells. 6. It is concluded that the lipoprotein lipase responsible for the hydrolysis of VLD lipoprotein triacylglycerol is predominantly located externally to the heart muscle cells and that its release can be facilitated by perfusion of the heart with bacterial collagenase.