Blood Acetate Research Articles

Origins of blood acetate in the rat

A novel enzymimc cycling assay for the determination of acetate in biological material is described. Measurements of the acetate concentration in blood and liver samples from rats of various ages and nutritional states with this assay are reported. The contribution of the intestine, the liver and the rest of the body to maintaining the concentration of acetate in the circulation is examined. Evidence is presented that the gut flora constitute the main source of acetate in blood of fed adult rats, though endogenous production of acetate is of significance in other situations. The streptozotocin-diabetic rat has an elevated blood acetate concentration.

Kinetics of infused acetate and effect on plasma pyruvate and lipid concentrations in uremic and non-uremic dogs.

During acetate infusion at a rate of 10 millimoles/kg/hr arterial blood acetate levels rose progressively to maximums of 7.9 +/- 1.7 mM in uremic dogs and 10.8 +/- 1.4 mM in non-uremic dogs. Following cessation of infusion, removal of acetate followed first order kinetics. Acute uremia had no significant effect on mean clearance rates of acetate (1.28 +/- 0.28 L/kg/hr uremics vs 0.92 +/- 0.22 in non-uremics) or upon blood half-life of acetate following infusion (9.7 min. vs 10.9 min.). Plasma pyruvate levels rose during infusion from 1.5 to 4.4 mg/dl in the uremic dogs and following infusion rose further to 6.5 mg/dl. In the non-uremic dogs pyruvate was not significantly elevated until 30 min. post-infusion. Plasma free fatty acids increased from 79 to 131 mumoles/dl during acetate infusion in the uremic dogs, but did not change significantly in the non-uremic group. Plasma cholesterol and triglycerides increased after induction of uremia, but showed no significant changes as a result of acetate infusion in either group. These results suggest that the electrolyte and lipid abnormalities that occur in hemodialyzed uremic patients may be related to the acetate load these patients receive during dialysis.

Medroxyprogesterone acetate, estradiol, FSH and LH in peripheral blood after intramuscular administration of depo-provera® to women

The peripheral blood levels of medroxyprogesterone acetate (MPA), estradiol, FSH and LH were measured after an intramuscular injection of 150 mg and 300 mg of Depo-Provera® in three women. The radioimmunoassay used measured levels of medroxyprogesterone 5 — 10 times lower than previously reported following intramuscular injection of 150 mg Depo-Provera. No evidence for accumulation of the drug was found. Ovulation was suppressed during treatment. The levels of estradiol remained in the range of the early follicular phase of the untreated cycle, as did FSH and LH. The levels of LH were lower than those of FSH. MPA at levels ranging from 0.5 to 10 ng/ml suppresses ovulation by inhibition of the development of follicles.

Some aspects of foetal and uteroplacental metabolism in cows with indwelling umbilical and uterine vascular catheters.

1. The experiments were carried out on conscious pregnant Jersey cows with intravascular catheters implanted during late gestation in umbilical and uterine vessels. All but three of fifteen animals delivered live healthy calves. 2. Rountine daily analyses were made of blood gas tensions, pH and packed cell volume in foetal and maternal blood; plasma concentrations of glucose, fructose, lactate and urea were also determined. Measurements of plasma free fatty acids and blood acetate concentrations were made less frequently. Foetal heart rate and arterial blood pressure were recorded in animals with an umbilical arterial catheter. 3. The concentration differences between foetal and maternal blood or plasma in glucose, urea and acetate were measured in fifteen animals. The maternal-to-foetal glucose and acetate gradients across the placenta were high while the foetal-to-maternal plasma urea differences were small. 4. In those animals with patent arterial and venous catheters, uterine and umbilical blood flows were measured together with the arteriovenous differences in 02, glucose, acetate and lactate so that rates of foetal and uterine consumption could be estimated. The rates of utilization of O2, glucose and acetate by the foetus were lower than the values for the whole uterus, while the uteroplacental metabolism of these substrates was very high. 5. Significant amounts of lactate, which appeared to be produced by the uteroplacental tissue, were utilized by the foetus; the remainder passed into the uterine venous blood. 6. The total substrate/O2 quotient for the foetus, calculated from the utilization of known metabolites, appeared to be greater than 1. Thus, in the calf some carbon accumulation from sources other than amino acids, the uptake of which was not measured, would seem to occur. These results and the metabolic activity of the uterine tissues are discussed in relation to comparable findings in the sheep.

Relationship of Insulin Concentration to Blood Metabolites in the Dairy Cow

Jugular blood samples were taken at regular intervals from 31 ketosis-prone cows from 2 wk prepartum to 7 wk postpartum. Eleven cows exhibited elevated blood ketones and depressed blood glucose indicative of subclinical ketosis. There were no significant differences between means of normal and subclinically-ketotic cows in serum insulin or blood metabolites prior to calving. However, in early lactation, those cows which developed ketosis showed depressed serum insulin, blood glucose, and plasma triglycerides with elevated ketones, acetate in blood, and free fatty acids and cholesterol in plasma. Milk production was also lower in ketotic cows. Correlations within cow between serum insulin and glucose, total ketones, acetate of blood and free fatty acids, triglycerides, and cholesterol in plasma were .014, −.307, .080, −.421, .413, and −.002 for normal cows and .348, −.425, −.324, −.317, .298, and −.131 for subclinically-ketotic cows. It is suggested that low insulin during ketosis is a reflection of depressed blood glucose and, consequently, adipose lipolysis and hepatic ketogenesis are accentuated while acetate utilization and hepatic triglyceride release are depressed.

Blood and Liver Metabolites in Fed and Fasted Diabetic Goats

Two trials were to study alloxan diabetes in goats. The data were grouped: 1) normal fed goats (10); 2) 48-h fasted goats (5); 3) fed goats sampled 96h after alloxan treatment (5); and 4) goats treated with alloxan following a 48-h fast and sampled 96h after alloxan treatment with continued fasting (3). Groups 1 and 4 exhibited the following means: serum insulin 43.9, 16.4, 9.4, and 6.7μU/ml; blood glucose 55.0, 47.3, 219.6, and 485.6 mg/100ml; blood ketones 4.3, 2.6, 36.6, and 28.6 mg/100ml; blood acetate 4.7, 4.0, 42.7, and 4.9 mg/100ml; plasma-free fatty acids 1.8, 10.0, 14.4, and 40.5 mg/100ml; and plasma triglyceride 13.3, 7.0, 47.6, and 12.2 mg/100ml. Liver samples from five fed goats before and 12 days after alloxan treatment exhibited the following means: phospholipid 27.5 and 26.1 mg/g; triglyceride 21.2 and 98.9 mg/g; and percent lipid 7.2 and 14.4. The diabetes was accompanied by fatty liver development and probably reduction in utilization of acetate and triglyceride in the fed animals.

Acetate as a metabolic substrate in the fetal lamb.

Fetal acetate metabolsim was studied in chronically catheterized fetal lambs of 110-141 days' gestation. Acetate concentration was measured enzymatically in whole blood drawn simultaneously from maternal and fetal pre- and postplacental vessels. The oxygen content of the fetal blood samples was also measured. Fetal umbilical venous acetate concentration was found to be proportional to the maternal arterial acetate concentration and had a mean value of 0.366 mM. Fetal blood acetate increased significantly, by a mean of 0.081 mM, during circulation through the placenta. This increase was proportional to both the maternal acetate concentration and the concentration gradient of acetate across the placenta. The mean maternal arterial acetate concentration was 1.153 mM. Maternal blood lost significant amounts of acetate, 0.112 mM, during circulation through the uterus and appeared to be the source of the acetate being gained by the fetus. It is estimated that a total of 23 mmol of acetate/kg of fetal weight is being taken up by the fetus each day, providing it with 0.560 g of carbon/kg. Comparisons of acetate uptake with fetal oxygen uptake indicate 10% of the daily fetal oxygen consumption would be required to completely oxidize the acetate being gained by the fetus.

Glucose and acetate metabolism in sheep at rest and during exercise.

Total entry rate of blood glucose and the rate of irreversible loss of blood acetate and its oxidation have been examined in sheep at rest and while walking on a horizontal treadmill at 5 km/h for 2 h. Sheep were given their daily ration of 1000 g chaff in 24 eaual portions at hourly intervals and received multiple intravenous injections of [2-3H]glucose and intravenous infusions of [1-14C]acetate and NaH14CO3. At rest the total entry rate of blood glucose was 0-44 +/- 0-03 mmol/min (values given as mean +/- s.e.m. for four sheep), the glucose pool was 23 +/- 1 mmol and the rate of irreversible loss of blood acetate was 2-3 +/- 0-1 mmol/min. During exercise, the total entry rate of blood glucose was 0-84 +/- 0-04 mmol/min, the glucose pool was 27 +/- 2 mmol and the rate of irreversible loss of blood acetate was 2-6 +/- 0-1 mmol/min. Gluconeogenesis apparently increased markedly in response to exercise as indicated by the incorporation of 14C from blood bicarbonate into blood glucose. Despite the substantial increase in the rate of irreversible loss of blood bicarbonate (from 11-6 +/- 1 to 20-2 +/- 2 mmol C/min), and hence energy expenditure with exercise, only a slight change was recorded in the proportion of the irreversible loss rate of acetate that was oxidized.

Production of Endogenous Acetate by the Liver in Lactating Ewes

The production of endogenous acetate by the liver has been investigated in lactating ewes using animals with indwelling arterial, and portal and hepatic venous cannulae. The capacity of the liver to produce acetate from acetyl-CoA in vitro has also been examined using homogenates prepared from liver biopsy samples. Mean arterial, portal and hepatic venous blood acetate concentrations in four ewes at 4 weeks lactation were 0.40, 1.00 and 1.46 mM respectively. The mean exogenous and endogenous acetate production rates were 56 and 54 mmol/h respectively, giving a total of 110 MMOL/h. The mean portal-hepatic venous difference in free fatty acid concentration was 81 muM. Converting this uptake of free fatty acids by the liver (based on palmitate as a standard) to 2-carbon equivalents, the acetate produced accounted for 70% of the fatty acids taken up. The correlation coefficient (r2) between uptake of free fatty acids and production of acetate by the liver was 0.83 (P less than 0.01). Calculation of the net acetate production in vivo gave a mean value for the production of acetate of 0.75 nmol/min. Calculation of the in vitro enzymic capacity of the liver to produce acetate from acetyl-CoA gave a mean of 0.94 mmol/min. These results indicate that enzymic production of acetate from acetyl-CoA, via carnitine acetyltransferase and acetylcarnitine hydrolase (see Costa and Snoswell 1975a), can adequately account for the substantial production of acetate by the liver in lactating ewes.

Biochemical changes induced by ethyl acetate in blood and liver of rat.

Biochemical changes induced by ethyl acetate in blood and liver of rat.

Production and utilization of acetate in mammals.

1. In an attempt to define the importance of acetate as a metabolic precursor, the activities of acetyl-CoA synthetase (EC 6.2.1.1) and acetyl-CoA hydrolase (Ec 3.1.2.1) were assayed in tissues from rats and sheep. In addition, the concentrations of acetate in blood and liver were measured, as well as the rates of acetate production by tissue slices and mitochondrial fractions of these tissues. 2. Acetyl-CoA synthetase occurs at high activities in heart and kidney cortex of both species as well as in rat liver and the sheep masseter muscle. The enzyme is mostly in the cytosol fraction of liver, whereas it is associated with the mitochondrial fraction in heart tissue. Both mitochondrial and cytosol activities have a K(m) for acetate of 0.3mm. Acetyl-CoA synthetase activity in liver was not altered by changes in diet, age or alloxan-diabetes. 3. Acetyl-CoA hydrolase is widely distributed in rat and sheep tissues, the highest activity being found in liver. Essentially all of the activity in liver and heart is localized in the mitochondrial fraction. Hepatic acetyl-CoA hydrolase activity is increased by starvation in rats and sheep and during the suckling period in young rats. 4. The concentrations of acetate in blood are decreased by starvation and increased by alloxan-diabetes in both species. The uptake of acetate by the sheep hind limb is proportional to the arterial concentration of acetate, except in alloxan-treated animals, where uptake is impaired. 5. Acetate is produced by liver and heart slices and also by heart mitochondrial fractions that are incubated with either pyruvate or palmitoyl-(-)-carnitine. Liver mitochondrial fractions do not form acetate from either substrate but instead convert acetate into acetoacetate. 6. We propose that acetate in the blood of rats or starved sheep is derived from the hydrolysis of acetyl-CoA. Release of acetate from tissues would occur under conditions when the function of the tricarboxylic acid cycle is restricted, so that the circulating acetate serves to redistribute oxidizable substrate throughout the body. This function is analogous to that served by ketone bodies.

The metabolism of glucose, acetate, lipids and amino acids in lactating dairy cows

SUMMARYSpecialized techniques, previously used in surgically prepared goats, which simultaneously measure udder metabolism (arteriovenous difference of milk precursors x udder blood flow) and the whole body turnover of the milk precursors, have been successfully transferred to dairy cows. Methods of obtaining representative samples of arterial and mammary venous blood and of measuring udder blood flow are described.The rates of entry into the circulation, as determined by isotope dilution, of glucose, acetate and plasma free fatty acids were 3·3–4·0, 1·7–2·1 and 0·5 kg/day respectively. Acetate and glucose contributed 32–50 and 4–11% respectively of the total CO2output by the animal.Measurement of the uptake of precursors of milk constituents and their transfer into milk showed that there were substantial arteriovenous differences of glucose, acetate, triglyceride and β-hydroxybutyrate which were not significantly different between breeds or related to milk yield. Isotopic and balance data confirm that glucose is the main precursor of lactose and that the oxidation and transfer of glucose into lactose accounted for 69–98% of the glucose entry rate. As in the goat, plasma triglycerides and blood acetate accounted for 35–80% and 25–50% of the milk triglycerides respectively. Propionate was extracted from plasma but the uptake was only about 8% of the value for acetate.There was no net arteriovenous difference of phospholipids, cholesterol esters or free fatty acids, but the fall in specific radioactivity of free fatty acids across the mammary gland indicated there was an exchange of free fatty acids between plasma and mammary tissue. In agreement with previous findings, acetate contributed to all the milk fatty acids up to a chain length of C14and part of the C16fatty acid. Plasma triglycerides contributed to the remainder of the C16 fatty acid and all the milk fatty acids with a chain length of C18or higher.In contrast to the lactating goat, cow plasma contained very few chylomicrons. The majority of the triglycerides taken up by the udder were derived from the lowdensity lipoprotein fraction.The essential amino acids were extracted from blood in amounts sufficient to account for the essential amino acids secreted into milk protein. Although the plasma level of methionine was low, 52–72% of the material reaching the mammary gland was taken up. The uptake of arginine was far in excess of the requirement for milk protein synthesis.

Studies on the mode of uptake of blood triglycerides by the mammary gland of the lactating goat. The uptake and incorporation into milk fat and mammary lymph of labelled glycerol, fatty acids and triglycerides.

1. The mode of uptake of the precursors of milk fat by the mammary gland of the lactating goat has been examined by infusing radioactive fatty acids, glucerol or doubly labelled triglycerides into the mammary artery or jugular vein of animals surgically prepared to permit samples of arterial and venous blood to be withdrawn without disturbance to the animal. 2. Acetate was taken up by the mammary gland and incorporated into milk fat. The decrease in the specific radioactivity of blood acetate across the gland was evidence of acetate production, but there was no significant release of labelled lipid from the mammary gland. 3. When labelled long-chain fatty acids or glycerol were infused into the lactating goat, there was extensive transfer of radioactivity into milk in spite of the absence of net uptake of substrate by the mammary gland. The decrease in the specific radioactivity of each substrate across the mammary gland, however, showed that both fatty acids and glycerol were simultaneously taken up and released by mammary tissue. 4. The infusion of chylomicra and triglyceride emulsions labelled with (3)H and (14)C revealed that both glycerol and fatty acids were released during triglyceride uptake by mammary tissue. Changes in the (3)H/(14)C ratio during the transfer of triglyceride from blood into milk showed that at least 80% of the triglyceride was hydrolysed during uptake, but the potential re-utilization of both products of hydrolysis for triglyceride synthesis in mammary tissue implied that only a minimum value could be obtained from the change in the ratio. 5. The time-course of the transfer of (3)H and (14)C into milk and lymph were closely similar after the infusion of [2-(3)H]glycerol tri[1-(14)C]oleate or of a mixture of [2-(3)H]glycerol and [1-(14)C]oleate. 6. The results were consistent with the hypothesis that plasma triglycerides are extensively or completely hydrolysed during mammary uptake.

Effect of Feeding Soybeans or Formaldehyde-Treated Soybeans on Lipid Metabolism in Ruminants

Three lactating fistulated goats were used in a 3×3 Latin Square design comparing control, formalin-treated, and untreated soybean rations. The concentrate-to-roughage ratio was 2:1.Milk yield was depressed (P<.05) in the formalin-treated soybean group. Long chain unsaturated milk fat fatty acids increased in both soybean treatments compared to controls with no significant difference between treated and untreated beans. Rumen pH and total protozoa counts were lower on the goats fed formaldehyde-treated beans. Total rumen lipids were elevated over controls in both treatments. Unsaturated 18 carbon fatty acids in the rumen lipids were higher with the treated soybeans compared to the untreated beans, suggesting some protection of the soybean lipids from hydrogenation. The inclusion of soybeans appeared to depress butyrate production and significantly increase propionate production in the rumen. Circulating blood acetate was depressed (P<.05) with the formaldehyde treatment. Plasma and fecal lipid levels and milk fatty acids suggested that the soybean lipids were being utilized in both treatments but with no distinct advantage for the treated soybeans.

Effect of insulin administration on blood acetate and feed intake of sheep.

Effect of insulin administration on blood acetate and feed intake of sheep.

Effects of the Addition of Bentonite to High-Grain Dairy Rations which Depress Milk Fat Percentage

Twelve lactating Holstein cows were placed on an experiment consisting of three periods: four-week normal control, six-week fat depression, and six-week treatment. In the last period the cows were divided into three groups and allotted to three treatments: I. Fat-depressing ration, II. Fat-depressing ration + 5% bentonite, and III. Fat-depressing ration + 10% bentonite.A highly significant increase in milk fat per cent was noted in both bentonite treatments versus the fat-depressing ration, but there was no significant difference between the two levels of bentonite. The cows in Treatments I, II, and III maintained per cent milk fat at 86, 144, and 144% of the fat-depressing period, and 60, 87, and 87% of the normal control period, respectively. Milk production was significantly higher for Treatment II. A significant increase in the proportion of rumen acetate, along with a decrease in propionate and valerate, was noted in the two bentonite treatments compared to the fat-depressing ration. There was a significant increase in the arteriovenous difference of blood acetate in the two bentonite treatments compared to the fat-depressing ration. Arteriovenous differences for blood glucose and ketones and plasma free fatty acids and triglycerides were not altered significantly.

Metabolic effects of haemodialysis against glucose- and acetate-containing solutions

Blood acetate, lactate, pyruvate and glucose have been measured in two groups of patients undergoing haemodialysis; five patients with acute or terminal chronic renal failure who had not previously been dialysed and five patients on chronic haemodialysis. There were significant rises in blood levels of all these compounds, with no significant differences between the two groups. It is concluded that the body is capable of metabolising the acetate received during haemodialysis even in advanced uraemia.

Volatile fatty acids in the digestive tract of the fowl.

1. Examination of the digesta from all regions of the avian digestive tract showed that volatile fatty acids (VFAs) were present in greatest concentration in the caeca and that they comprised mainly acetic, propionic and butyric acids.2. All droppings contained VFAs but they were present in highest concentration in those of caecal origin. Caecectomy was followed by a marked reduction in the total output of VFAs.3. Birds 14–20 weeks of age had similar concentrations of VFAs along the tract and similar numbers and distribution of micro-organisms.4. Portal blood contained all the VFAs found in the digestive tract whilst peripheral blood contained only acetic and formic acids.5. The almost complete absence of VFAs from the tract contents of germ-free birds showed that the VFAs normally present in the tract were of microbial origin.6. The presence of similar levels of acetate in the peripheral blood of conventional and germfree birds indicated that circulating acetate was mainly of endogenous and not microbial origin.7. The significance of VFAs as an energy source is discussed.

Origin of Glyceride Fatty Acids in Cow Milk Fat

To elucidate further the origin of milk fatty acids, the patterns of their specific activities following a single intravenous injcetion of 1-14C-CH3COONa were compared with those resulting from continuous infusion over a period of up to 30 hours. Throughout, the specific activities of the milk fatty acids were much higher than those of the blood. The current view that milk fatty acids up to C14 are synthesized from blood acetate, and that C16:0 and especially C18:0 are derived mainly from blood glycerides, was confirmed by the single injection experiment. On the other hand, with continuous infusion, the milk fatty acids, on the basis of the patterns of specific activities, were divisible into three groups—C2:0 to C10:0, C12:0 to C16:0, and C18:0, C18:1, consistent with their formation by different routes. The eventual elevation of the specific activity of C16:0 to that of the lower fatty acids is consistent with its formation mainly from blood acetate, albeit by a slower pathway. The origin of part of the C18:0 from acetate is likewise indicated. The relatively high specific activity of C18:1 in relation to C18:0, in one experiment particularly, suggests that oleic acid also may be synthesized from sources other than stearic acid.

The oxidation and utilization of palmitate, stearate, oleate and acetate by the mammary gland of the fed goat in relation to their overall metabolism, and the role of plasma phospholipids and neutral lipids in milk-fat synthesis

1. Measurements were made of milk yield, mammary blood flow and arteriovenous differences of each plasma lipid fraction, and their specific radioactivities, during the infusion of [U-(14)C]stearate, [U-(14)C]oleate, [U-(14)C]palmitate and [1-(14)C]acetate into fed lactating goats. 2. Entry rates of fatty acids into the circulation were 4.2mg./min./kg. body wt. for acetate, and 0.18, 0.28 and 0.42mg./min./kg. for stearate, oleate and palmitate respectively. Acetate accounted for 23% of the total carbon dioxide produced by the whole animal, and contributed to the oxidative metabolism of the mammary gland to about the same extent. Corresponding values for each of the long-chain acids were less than 1%. 3. There were no significant arteriovenous differences of phospholipids, sterols or sterol esters, and their fatty acid composition showed no net changes during passage through the mammary gland. 4. There were large arteriovenous differences of plasma triglycerides, and their fatty acid composition showed marked changes across the gland. The proportions of palmitate and stearate fell, and that of oleate increased. 5. Arteriovenous differences of plasma free fatty acids (FFA) were small and variable, but a large fall in the specific radioactivity of each of the long-chain acids examined indicated substantial uptake of plasma FFA, accompanied by roughly equivalent FFA release from mammary tissue. The uptake of FFA was confirmed by the extensive transfer of radioactivity into milk. The FFA of milk were similar in composition and radioactivity to the milk triglyceride fatty acids, and quite unlike plasma FFA. 6. The formation of large amounts of oleic acid (18-21 mg./min.) from stearic acid was demonstrated. 7. During the terminal stages of the [(14)C]acetate infusion, milk triglyceride fatty acids of chain length C(4)-C(14) showed specific radioactivities that were 75-90% of that of blood acetate, and that of palmitate was roughly one-quarter of this value. Oleate and stearate were unlabelled. 8. The results confirmed that milk fatty acids of chain length C(4)-C(14) arise largely from blood acetate, and palmitate is derived partly from acetate and partly from plasma triglyceride, the latter fraction being almost the sole precursor of oleate and stearate.