Free Fatty Acid Availability Research Articles

Glucose production in the perfused dog liver: Effect of free fatty acids and ketones

The perfused rat liver model has been used widely for the past 30 years to investigate various aspects of hepatic metabolism. Certain aspects of the regulation of glucose production, however, are different in rats and in higher mammals. A method for perfusing dog livers in situ has been developed. It is easier to perform and to standardize than previously described techniques, and enables the direct effect of various substances on glucose production to be tested. This new approach has been used to assess the influence of ketones and albumin-bound free fatty acids (FFA) on total hepatic glucose output. In contrast to the response generally observed in the rat, it was found that an increased availability of FFA or ketones caused a net decrease in glucose output from the dog liver. Thus, perfusion of the dog liver is a feasible technique that is particularly useful because the responses in rats and dogs are not always the same.

Fatty acid supply and organ phospholipid turnover in two canine shock models

Serum free fatty acid (FFA) flux is decreased in shock. The question arose whether the limited availability of FFA would result in a fuel deficit in organs containing no stored lipid and also in the slower turnover of organ phospholipids. The fasting dog's lung, stomach, heart, and liver contained little or no triglyceride, while skeletal muscle, diaphragm, and occasionally intestine had large lipid stores. The replacement rate of lipid fuels and the turnover rate of the fatty acyl moieties of phospholipids were determined by radioactive tracer methods in several organs of dogs in shock due to controlled cardiac tamponade or hemorrhage and their respective controls. In the normotensive controls one-third of the FFA available was directly oxidized; the rest was temporarily incorporated into phospholipids and triglycerides. This incorporation represents replacement of lipid fuels in the organs. Both shock models caused a similar decrease in the total FFA flux and a similar pattern of redistribution among organs. Organs other than heart, lung, and diaphragm replenished their lipid stores slowly in shock. This could cause a fuel deficit in liver and stomach, neither of which have large triglyceride stores. FFA incorporation into phospholipids was slower than esterification into triglycerides in all organs except diaphragm and skeletal muscle both in shock and in normotension. The rate of phospholipid turnover decreased significantly in shock in liver, intestine, and stomach, but increased in heart and lung. Thus liver and stomach are the organs most likely to be affected by the decreased availability of FFA in shock.

Influence of fasting on glycogen depletion in rats during exercise.

We recently observed that a 24-h fasted group of rats could run longer than an ad libitum fed control group before becoming exhausted. Because of the demonstrated importance of glycogen levels and free fatty acid availability during endurance exercise, we have investigated several parameters of carbohydrate and lipid metabolism in exercised and nonexercised rats that were either fed ad libitum or fasted for 24 h. A 24-h fast depleted liver glycogen, lowered plasma glucose concentration, decreased muscle glycogen levels, and increased free fatty acid and beta-hydroxybutyrate concentrations in plasma. During exercise the fasted group had lower plasma glucose concentration, higher plasma concentration of free fatty acids and beta-hydroxybutyrate, and a lower muscle glycogen depletion rate than did the ad libitum fed group. Since fasted rats were able to continue running even when plasma glucose had dropped to levels lower than those of fed-exhausted rats, it seems unlikely that blood glucose level, per se, is a factor in causing exhaustion. These results suggest that fasting increases fatty acid utilization during exercise and the resulting "glycogen sparing" effect may result in increased endurance.

Fetal and neonatal responses to extended maternal canine starvation. I. Circulating fuels and glucose and lactate turnover.

Summary: The effect of maternal starvation for 5 days on circulating fuels, on glucose, and on lactate turnover in fasted newborn dogs was studied at 0, 3, 6, 9, and 24 h of age. Maternal starvation reduced the birthweight of the puppies by 23% (232 ± 6 versus 300 ± 10 g). Fetal ketone body concentration (3.33 μmole/ml) paralleled the marked maternal hyperketonemia (5.78 μmole/ml).After birth, maternal canine starvation (MCS) also caused significantly lower fasting blood glucose values in the pups at 3 h of age compared to controls (2.79 versus 5.77 μmole/ml). In addition, plasma free fatty acids (FFA) and glycerol levels were significantly reduced at 3 h of age. At 6 h, glucose and FFA concentration became equivalent to controls. Glycerol concentration, however, remained depressed at 6 and 9 h, and plasma triglyceride levels were significantly elevated. A significant rise in blood alanine concentration was observed at 3, 6, and 24 h of age in MCS pups. In spite of low blood glucose values at 3 h of age, the glucose production rate (GPR) in the MCS pups was the same as in the controls. Lactate turnover and its carbon incorporation into glucose did not show any significant differences between MCS and control pups at individual time points.These data suggest that during starvation the mother was unable to provide sufficient substrates for normal fetal growth. Maternal and fetal nutrient deficiency may have resulted also in decreased neonatal blood glucose levels together with reduced lipolysis in the immediate newborn period. Circulating glucose, FFA, and glycerol concentrations reached control values during the remainder of the study. Diminished availability of FFA may have resulted in enhanced tissue clearance of glucose. When lipolysis increased and peripheral tissue had an alternate fuel, glucose clearance returned to control values. The precise mechanism for the diminished levels of circulating fuels among fasted pups after 5 days of maternal starvation was not directly evident from these investigations of circulating fuels and glucose or lactate turnover data.

Effect of fatty acids on lipid and apoprotein secretion and association in hepatocyte cultures.

Increasing availability of free fatty acids (FFA) to liver results in enhanced rates of secretion of triglycerides in lipoproteins. However, as FFA uptake increases, triglyceride secretory rates reach a plateau and esterified fatty acids accumulate intracellularly, suggesting that something is limiting lipid transport out of the liver. One possibility could be the limited availability of apoproteins. To test this hypothesis, primary rat hepatocytes in culture were incubated with increasing amounts of FFA (0-2.1 mumol/dish) and the amounts of lipids and apoproteins inside the cells and in culture media were measured; the latter by specific radioimmunoassays. Media also were fractionated on Sepharose 2B and 6B columns and the elution profiles of apoproteins were obtained. With exposure to increasing amounts of free fatty acids, hepatocytes took up more fatty acids and intracellular levels of triglycerides rose (from 71 to 146 micrograms/mg cell protein). Concomitantly, media triglycerides nearly doubled (31 to 51 micrograms/mg). Incorporation of [3H]glyceride into cellular and media triglyceride also rose. However, levels of apoproteins A-I, B, C-III3, and E in cells and media were unchanged. The increasing amounts of triglycerides in media were present in larger particles, as demonstrated on gel permeation chromatography. The elution profiles of apoproteins B, C-III3, and E were altered in that a greater proportion of the apoproteins eluted with larger particles. Similar results were obtained when hepatocytes were preloaded with increasing amounts of FFA over 12 h and analyses of cells and media were carried out 8 and 22 h after removal of fatty acids from the media. During loading of cells, accumulation of cellular triglycerides was directly related to media FFA concentrations. During unloading, triglyceride secretory rates were related to cellular triglyceride levels. At higher triglyceride secretory rates larger particles were secreted and a greater proportion of apoproteins was associated with the larger particles, but total amounts of apoproteins in the system did not change. These data lead us to suggest that enhanced rates of apoprotein synthesis need not occur in the response to acute changes in hepatic lipid transport, rather, increased secretion of lipid is brought about by augmented intracellular lipid apoprotein association.

Effects of free fatty acid availability, glucagon excess, and insulin deficiency on ketone body production in postabsorptive man.

The present studies were undertaken to assess the relative effects of free fatty acid (FFA) availability, glucagon excess, and insulin deficiency on ketone body (KB) production in man. To determine whether an increase in FFA availability would augment KB production in the absence of insulin deficiency and glucagon excess, plasma insulin and glucagon were maintained at basal concentrations by infusion of somatostatin and exogenous insulin and glucagon, and plasma FFA were increased from 0.32 +/- 0.06 to 1.4 +/- 0.1 mM by a 2.5-h-infusion of a triglyceride emulsion plus heparin. KB production increased fivefold from 2.2 +/- 0.4 to 11.4 +/- 1.2 mumol . kg-1 . min-1, P less than 0.001. To determine whether insulin deficiency would further augment KB production, analogous experiments were performed but the replacement infusion of insulin was stopped. Despite a greater increase in plasma FFA (from 0.26 +/- 0.04 to 1.95 +/- 0.3 mM), KB production increased (from 1.5 +/- 0.3 to 11.1 +/- 1.8 mumol . kg-1 . min-1) to the same extent as in the absence of insulin deficiency. To determine whether hyperglucagonemia would augment KB production beyond that accompanying an increase in plasma FFA and, if so, whether this required insulin deficiency, similar experiments were performed in which the glucagon infusion rate was increased to produce plasma glucagon concentrations of 450-550 pg/ml with and without maintenance of the basal insulin infusion. When basal plasma insulin concentrations were maintained, hyperglucagonemia did not further increase KB production; however, when the basal insulin infusion was discontinued, hyperglucagonemia increased KB production significantly, whereas no change was observed in saline control experiments. These studies indicate that, in man, FFA availability is a major determinant of rates of KB production; insulin does not appear to influence ketogenesis rates by a direct hepatic effect, and glucagon can further augment KB production when FFA concentrations are increased but only in the setting of insulin deficiency.

Effects of free fatty acids, insulin, glucagon and adrenaline on ketone body production in humans.

In normal human subjects, when plasma insulin, glucagon and growth hormone were 'clamped' at basal concentrations (by infusion of somatostatin plus replacement infusion of these hormones), infusion of Intralipid and heparin increased plasma free fatty acid (FFA) concentrations to approx. 1.3 mM, and ketone body production increased 4-5 fold to approx. 11 mumol . kg -1 . min-1. Hyperglucagonaemia did not further increase ketogenesis. In conditions of combined insulin and glucagon deficiency (by infusion of somatostatin without insulin and glucagon), administration of Intralipid and heparin increased plasma FFA concentrations to approx. 2.2 mM but a further increase in ketone body production did not accompany this increase. In these conditions hyperglucagonaemia increased ketogenesis by 2-3 fold the increment seen in control studies. Infusion of adrenaline (epinephrine) in conditions in which insulin secretion was not inhibited caused only a transient increase in plasma FFA concentrations and in ketone body production. These data indicate: (1) that in humans increased FFA availability can markedly augment ketogenesis in the absence of insulin deficiency and without hyperglucagonaemia; (2) that glucagon can increase ketone body production during insulin deficiency but not in its absence; and (3) that insulin deficiency may be accompanied by increased ketogenesis only because of a lack of its restraint on lipolysis and because of the action of glucagon. Glucagon may be important in determining the magnitude of ketone body production for a given degree of FFA availability and insulin deficiency, and may be necessary for attainment of maximal rates of ketogenesis. Adrenaline increases ketone body production in humans, but whether this is primarily due to a direct effect on the liver or is mediated through enhancement of lipolysis remains to be determined.

Cholesterol esters and the ester-metabolizing enzymes in Jimpy and Quaking mouse brains

The concentration of free and esterified cholesterol and the activities of the cholesterol esterifying enzyme and cholesterol ester hydrolases in brains from Jimpy and Quaking mice and their normal littermates were determined. In Quaking affected mice these brain components did not differ significantly from those in brains of normal littermates. In the Jimpy affected mouse brain, however, the concentration of free cholesterol was reduced and the esterified cholesterol was increased. The increase in esterified cholesterol was accompanied by higher activity of cholesterol esterifying enzyme and a significant reduction in activity of hydrolases. In the absence of exogenous fatty acids, cholesterol esterification by cell-free preparations of brain from Jimpy affected mice was also significantly higher than the normal littermates. These data indicate that an increase in cholesterol ester concentrations in Jimpy affected brain may result either from an increase in esterification due to an increase in the availability of free fatty acid as substrate, or from deficiency in the activity of the hydrolases. In addition, the data indicate that in Jimpy mutants there is a significant reduction in brain cholesterol content, whereas in Quaking mutants the sterol content of developing brain is not significantly affected. This suggests that during brain development sterol synthesis in brain is reduced in Jimpy but not in Quaking mutants.

Fasting plasma hormones and metabolites in feral and domestic newborn pigs.

Newborn Yorkshire and Ossabaw (feral) pigs were examined under thermoneutral conditions to determine whether survival rate during fasting differs between these breeds and whether any blood-borne factors are associated with improved survival. Newborn pigs were removed from the sow before suckling. Body composition was determined on 10 newborn Ossabaw and 12 newborn Yorkshire pigs. Another group of animals (eight Ossabaw, 12 Yorkshire) was fasted for 72 hr, with blood samples drawn at birth and 12 and 24 hr into fasting. Glucose, free fatty acid (FFA), growth hormone (GH), insulin, thyroxine (T4), triiodothyronine (T3), cortisol and glucagon concentrations were measured in plasma of fasted pigs. Concentrations of carcass lipid, dry matter and ash were higher in newborn Ossabaw pigs than in newborn Yorkshire pigs. Survival through 72 hr of fasting was lower among Yorkshire pigs. Yorkshire and Ossabaw pigs had similar concentrations of metabolites and hormones at birth, with the exceptions of lower plasma GH and higher T3 concentrations in Ossabaw pigs. Higher plasma T3 concentrations would indicate a greater potential for fatty acid oxidation. During fasting, Ossabaw pigs had lower plasma GH and T4 concentrations and higher glucagon and FFA concentrations. Increased survival among newborn Ossabaw pigs may have been due to increased availability of FFA during fasting, and to a greater potential for gluconeogenesis through increased oxidation of fatty acids and higher plasma glucagon concentrations. This would suggest that maternal treatments that would increase storage of fat and(or) increase the capacity for oxidation of fat in utero would improve survival of newborn pigs.

Effects of Prolonged Starvation on Plasma Free Fatty Acid Levels and Fatty Acid Composition of Myocardial Total Lipids in the Rat

Experiments were carried out on male rat fed ad libitum or starved for a period of 7 days. Plasma levels of free fatty acids (FFA) and the quantity and composition of fatty acids in total lipids of heart ventricular tissue in vivo were analyzed by gas liquid chromatography (GLC). In addition, FFA extraction ratios and uptake rates were determined in isolated perfused hearts using the classical Langendorff technique. After 7 days of starvation, distribution and concentrations obtained for total lipid fatty acids from heart ventricles of starved animals were substantially different from those of controls. In particular, 20:5 and 22:6 carbon polyunsaturated fatty acids were significantly elevated. Also, total plasma FFA level was elevated and FFA extraction ratios were increased as a result of prolonged starvation. Accumulation of 20- and 22-carbon polyunsaturated fatty acids observed in ventricles of starved rats may have resulted from increased availability and extraction of FFA.

Carbohydrate utilization in obese subjects after an oral load of 100 g naturally-labelled [13C] glucose.

1. Total carbohydrate (CHO) and ingested glucose oxidation was measured in five obese subjects with normal glucose tolerance after an oral load of 100 g naturally-labelled [13C]glucose using indirect calorimetry and mass spectrometry respectively. 2. CHO utilization rate (107 +/- 14 mg/min in the post-absorptive state) increased 30 min after the glucose load to reach a plateau (245 +/- 25 mg/min) between 90 and 120 min. It then decreased to basal values at 330 min. Cumulative CHO oxidation over 480 min was 66 +/- 7 g and the CHO oxidized above basal levels was 26 +/- 7 g. 3. Enrichment of expired carbon dioxide with 13C began at 45 min and maximum values were observed between 210 and 300 min. At 480 min, cumulative oxidation of the ingested glucose was 24 +/- 2 g. 4. Compared with controls, the obese subjects exhibit an impairment of CHO utilization which precedes glucose intolerance. This impairment can be explained by an increased availability of free fatty acids which favours lipid oxidation at the expense of ingested [13C]glucose oxidation.

Calcium-dependent modulation of guanosine 3′,5′-monophosphate in renal cortex: Possible relationship to calcium-dependent release of fatty acid

The effects of Ca 2+ on cGMP accumulation in rat renal cortical slices were correlated with the effects on 14C-fatty acid release in tissue prelabeled with 14C arachidonate. Ca 2+ in the presence and absence of ionophore A23187 exerted parallel effects on the release of labeled arachidonate from slices and on slice cGMP content. Thus, Ca 2+ stimulated both arachidonate release and tissue cGMP accumulation 2 to 3-fold when added to slices of renal cortex previously deprived of Ca 2+ and Mg 2+, whereas Mg 2+ had no stimulatory effect on either arachidonate release or tissue cGMP content. In the presence of A23187, Ca 2+ increased arachidonate release and tissue cGMP accumulation 4 to 6-fold. Tetracaine partially inhibited Ca 2+-induced arachidonate release and completely blocked Ca 2+-induced cGMP accumulation. Ca 2+-induced arachidonate release was unaffected by the absence of O 2. Addition of exogenous arachidonate to slices of renal cortex increased tissue cGMP content 2-fold. Linoleate exerted a lesser effect on tissue cGMP, while palmitate and oleate had no effect. Ca 2+- and arachidonateinduced cGMP contents in renal cortical slices were not additive, and both were abolished by exclusion of O 2. Since nitroprusside increased cGMP accumulation 10- to 15-fold in O 2-deprived slices, loss of the Ca 2+ and arachidonate responses under these incubation conditions was selective. Ca 2+-induced cGMP accumulation was unaffected by indomethacin (100 μg/ml), but was abolished by 200 μM 5,8,11,14-eicosatetraynoic acid (TYA). The results are consistent with the possibility that the Ca 2+-dependent processes regulating cGMP in renal cortex include Ca 2+-dependent acyl hydrolase activity, which limits the availability of free polyunsaturated fatty acids. A role for fatty acid oxygenation products in the stimulation of cGMP is suggested, but not established, by the O 2 dependence of the actions of both Ca 2+ and exogenous fatty acids. The failure of exogenous arachidonate or linoleate to mimic quantitatively the actions of Ca 2+ on cGMP may reflect the involvement of other Ca 2+- and O 2-dependent processes in modulation of cGMP in this tissue or limited access of exogenous fatty acid to cGMP regulatory sites in the cell.

Modified Copper Soap Solvent Extraction Method for Measuring Free Fatty Acids in Milk

A modified copper soap method was developed to provide a sensitive, rapid method for determining the free fatty acids in milk and estimating the intensity of lipolyzed flavor. The modification is simpler and more rapid than the original copper soap method. Only a small sample (.5ml) of milk is needed for this colorimetric test, so it would be feasible to take aliquots from a universal sample. The method can be semiautomatic with an automatic sampler and spectrophotometer with a flow-through cell to test up to 200 samples per hour. It would take approximately 2 days to run the equivalent number by the Bureau of Dairy Industry method.The coefficients of correlation between copper soap measures and flavor for nonhomogenized and homogenized milk were .83 and .82. The corresponding coefficients between Bureau of Dairy Industry measures and flavor were .67 and .78. Correlation between copper soap and Bureau of Dairy Industry milliequivalents per liter for 124 nonhomogenized milk samples was .90. The corresponding correlation for 109 homogenized samples was .88.A comparison of nonhomogenized and homogenized milk revealed that the availability of free fatty acids is less in homogenized milk. Fewer free fatty acids are recovered from homogenized milk by solvent extraction, and they have a lower sensory impact. Presumably some of the free fatty acids in homogenized milk are bound or entrapped.

In vitro palmitate and glucose metabolism in the postmature fetus

Fetuses from term and postmature rabbits were obtained and their livers incubated with palmitate-1-14C in room air. The net incorporation of the fatty acids into ketone bodies, lipids, and CO2 was measured at fixed and variable concentrations of cold glucose. Data from postmature liver show that lipid synthesis is decreased, 14CO2 production is increased, and ketone body formation is unchanged when compared with data from the term liver. The addition of cold glucose to a constant concentration of palmitate-1-14C causes a slight increase in lipid synthesis in the postmature liver, in contrast to a decrease in the term liver. The experimental results indicate that liver lipid synthesis and glucose utilization are diminished in the postmature preparation. This suggests that the postmature fetal liver responds to the decreased availability of free fatty acid from the placenta and to the increasing hypoxia by metabolic adaptations resembling those observed during fasting and tissue hypoxia. These changes are somewhat similar to those observed in the neonate before the onset of breast-feeding. Fetal metabolism is, therefore, responsive to changes in placental transfer of fatty acids and to postmaturity.

Correction of ketosis by suppression of lipolysis with 5-methylpyrazole-3-carboxylic acid in rats with established diabetic ketoacidosis.

Because the presence of an elevated plasma free fatty acid (FFA) concentration is not always sufficient to promote ketogenesis, we examined the contribution of circulating FFAs to ketogenesis in established diabetic ketoacidosis. We studied the effects of suppression of lipolysis on ketogenesis in rats with established streptozotocininduced diabetic ketoacidosis using 5-methylpyrazole-3-carboxylic acid (5-methylpyrazole) as an antilipolytic agent. In response to this substance, plasma FFA fell from 2.42 ± 0.15 meq/L to 0.56 ± 0.06 meq/L in four hours. There was a concomitant fall in total plasma ketone from 12.17 ± 0.60 mM to 2.62 ± 0.54 mM. The fall in total plasma ketone was due predominantly to a fall in the beta-hydroxybutyrate concentration but also to a fall in the acetoacetate concentration. Although the agent slowed the rise of plasma glucose in these diabetic animals, the concentration was markedly elevated (573 ± 22 mg/dl) at four hours. Studies were performed in comparable rats with diabetic ketoacidosis to exclude the possibility that 5-methylpyrazole interferes with hepatic ketogenesis. When the plasma FFA concentration was raised by administration of a lipid emulsion and heparin (after plasma FFA and total plasma ketone had fallen in response to 5-methylpyrazole), total plasma ketone also rose despite the presence of 5-methylpyrazole. When the plasma FFA concentration was maintained at a high level by administration of a lipid emulsion and heparin from the start of the experiment, 5-methylpyrazole failed to affect the total plasma ketone concentration. Thus, availability of substrate (plasma FFAs) reversed or prevented the correction of ketosis by 5-methylpyrazole. These findings indicate that circulating FFAs are rate limiting for the maintenance of the ketotic state in established diabetic ketoacidosis and support the view that the absence of ketosis in the usual patient with hyperosmolar nonketotic diabetic coma is a result of inadequate availability of plasma FFAs for ketogenesis. 5-Methylpyrazole converts an experimental model of diabetic ketoacidosis into one resembling hyperosmolar nonketotic diabetic coma.

Glucose-insulin-potassium infusion in acute myocardial infarction

A solution of 300 gm of glucose, 50 units of regular insulin, and 80 mEq of potassium chloride in 1,000 ml of sterile water infused at a rate of 1.5 ml/kg of body weight per hour can alter the availability of glucose and free fatty acids to the myocardium. Clinical studies of patients receiving this infusion less than 15 hours after the onset of symptoms of acute myocardial infarction suggest a reduction in mortality, an improvement in left ventricular mechanical performance, and a reduction in cardiac irritability as beneficial effects. Swan-Ganz catheterization for hemodynamic, electrophysiologic, and metabolic monitoring is recommended. Diabetics who require insulin and patients with impaired renal function are not candidates for the infusion. Further clinical studies are required before conclusions can be reached regarding the efficacy of glucose-insulin-potassium infusion in attempts to salvage damaged myocardium.

Effects of elevated plasma FFA and insulin on muscle glycogen usage during exercise.

Seven men were studied during 30 min of treadmill exercise (approximately 70% VO2 max) to determine the effects of increased availability of plasma free fatty acids (FFA) and elevated plasma insulin on the utilization of muscle glycogen. This elevation of plasma FFA (1.01 mmol/1) with heparin (2,000 units) decreased the rate of muscle glycogen depletion by 40% as compared to the control experiment (FFA = 0.21 mmol/1). The ingestion of 75 g of glucose 45 min before exercise produced a 3.3-fold increase in plasma insulin and a 38% rise in plasma glucose at 0 min of exercise. Subsequent exercise increased muscle glycogen utilization and total carbohydrate (CHO) oxidation 17 and 13%, respectively, when compared to the control trial. This elevation of plasma insulin produced hypoglycemia (less than 3.5 mmol/1) in most subjects throughout the exercise. These data illustrate the regulatory influence of both plasma insulin and FFA on the rate of CHO usage during prolonged severe muscular activity.

The turnover of blood glucose and plasma free fatty acids in the rat after acute carbon disulphide intoxication

The turnover of plasma free fatty acids and blood glucose has been measured in starved rats exposed to inhalation of carbon disulphide (2 mg/l) for 15 hr overnight. Measurements were made following single intravenous injection of [U- 14C]palmitic acid or of [5- 3H]glucose and [U- 14C]glucose in groups of exposed and control rats. CS 2 intoxication leads to a small but significant decrease in the rate of utilization of plasma free fatty acids and it is suggested that decreased availability of plasma free fatty acids leads to the increased catabolism of amino acids and the relatively large increase in urea production which is seen in starved CS 2-treated rats. Increased urea production is not associated with an increase in the absolute rate of production and utilization of blood glucose as measured using [5- 3H]glucose. There is an increase in the fractional turnover of blood glucose, but this is accompanied by a small hypoglycaemia in starved CS 2-treated rats. The fraction of glucose carbon which is recycled is unchanged in treated rats. A comparison has been made between fed and 24 hr-starved rats in their response to exposure to CS 2 (2 mg/l) for 4 hr. The results indicate that in contrast to starved rats, plasma free fatty acid utilization increases when fed rats are exposed to CS 2 and there is no increase in urea production. Inter-relationships between these effects are discussed.

The Effect of Short Term Physiological Elevations of Plasma Glucagon Concentration on Plasma Triglyceride Concentration in Normal and Diabetic Man

To explore the effect of physiological elevations of glucagon on plasma triglyceride concentration, glucagon was infused for thirty minutes at 3.0 ng/kg/min into both normal and insulin dependent diabetic subjects. The effects of this hormonal infusion on plasma triglyceride, free fatty acids, glucose, and insulin were compared to a control saline infusion study. A differential effect of glucagon on plasma triglyceride concentration between normal and diabetic subjects was observed. In normal subjects, glucagon infusion was accompanied by a concomitant increase in endogenous insulin secretion and free fatty acid levels, and no observable effect on circulating plasma triglyceride concentration. In contrast, in diabetic subjects, no change in insulin or free fatty acid concentration occurred during glucagon infusion and circulating plasma triglyceride concentration declined after twenty minutes of hormone infusion. These results suggest that plasma triglyceride concentration may be modulated, at least in part, by alterations in circulating plasma glucagon in concert with insulin secretion and free fatty acid availability in man.

Anti-ketogenic effect of glucose in the lactating cow deprived of food.

1. The aim of this study was to determine the effect of a constant infusion of glucose on the ketosis that is observed when dairy cows are deprived of food in early lactation. 2. Cows in early lactation were first deprived of food for 4 days (96h) to induce a 'fasting ketosis'. Glucose was then infused intravenously at a constant rate of 0.75 g/min for 48h while deprivation of food was maintained. At the end of this 48 h period, blood and liver ketone-body concentrations had decreased to values well below those found in healthy fed cows. 3. On the assumption that the anti-ketogenic effect of glucose was mainly due to suppression of hepatic ketogenesis, it was concluded that two anti-ketogenic mechanisms had been identified. These were (a) a decrease in the availability of free fatty acids for hepatic oxidation, and (b) anti-ketogenic changes within the liver itself. 4. These latter anti-ketogenic changes were twofold. The first was a major increase in the hepatic concentrations of citrate and 2-oxoglutarate. The second was an increase in the degree of oxidation of the hepatic cytosol. It was proposed that both these intrahepatic changes might indicate an augmentation of the quantity of oxaloacetate available for condensation with acetyl-CoA derived from fat oxidation. 5. Hepatic glycerol 1-phosphate concentration fell substantially after glucose infusion. 6. Glucose infusion into fed cows produced qualitatively similar effects to those observed in the unfed cows. However, blood and liver ketone-body concentrations were not decreased to the same extent in the fed cows as in the unfed cows.