Volatile fatty acid uptake and propionate metabolism in ruminant hepatocytes

Previous reports have demonstrated that butyrate inhibits metabolism of propionate by liver cells isolated from sheep and goats. Our objectives were to examine some possible mechanisms for this inhibition and to test for this inhibition in the bovine animal. Incorporation of label from 2.5 mM [2-(14)C]propionate into glucose (nmol propionate/mg cell DM/h) in the presence of 0, 1.25, and 2.5 mM butyrate was 107, 66, and 62 by goat hepatocytes and 79, 25, and 29 by calf hepatocytes; therefore, butyrate inhibited propionate metabolism at least as effectively in calves as in goats. In goat hepatocytes 1.25 mM butyrate reduced 1.25 mM propionate uptake to 46% of control, and 1.25 mM [2-(14)C] propionate incorporation into glucose to 44% of control. Propionate had no effect on butyrate uptake. Isovalerate and valerate tended to be cleared from the media to a greater extent than butyrate but had no effect on propionate uptake. Therefore, inhibition of propionate conversion to glucose by butyrate is specific and is not due to a general competition among VFA for metabolism. Butyrate inhibits hepatic propionate utilization generally, not specifically propionate conversion to glucose. Butyrate also inhibited propionate utilization by goat liver homogenates, indicating that butyrate inhibits propionate metabolism at a step subsequent to propionate transport across the hepatocyte plasma membrane.     

Endocrine changes with infusion of propionate in the dairy cow

Sodium propionate (2.5 mmol/kg) was infused rapidly via a jugular vein into each of 13 multiparous Holstein cows at 7 wk postpartum for observation of clearance of propionate. Associated concentration changes of acetate and glucose in blood plasma and glucagon and insulin in blood serum were quantified. This dose elevated concentrations of propionate, which declined subsequently at an exponential rate (.108 min-1). Concentrations of glucagon and insulin were increased in the sampling immediately following infusion, yet subsequent decline of insulin concentrations acted to decrease the molar ratio of insulin:glucagon as propionate returned to preinfusion concentrations. Analysis of sample means disclosed a negative correlation -.82 between glucose and molar ratio of insulin:glucagon. These experimental observations suggest that a supraphysiological dose of propionate has an immediate effect on the pancreas to alter endocrine secretion in the lactating cow.     

Effects of monensin on glucose metabolism in transition dairy cows

Eight multiparous periparturient Holstein cows fitted with ruminal cannula were used in a split plot design to evaluate the effects of monensin on plasma glucose metabolism. Diets were top-dressed daily with 0 mg/cow of monensin (control) or 300 mg/cow of monensin (MON) both pre- and postpartum. Plasma glucose kinetic parameters on d ?13 ± 2.0 and 19 ± 1.6 relative to parturition were determined by using stable isotopes. Na-1-¹³C₃-Propionate (labeled propionate) was infused into the rumen to measure glucose synthesis originating from ruminal propionate, and U-¹³C-glucose (labeled glucose) was injected into the jugular vein to determine total glucose kinetics. A sampling period of 480 min following labeled glucose injection was implemented. A compartmental analysis was employed to determine steady state glucose kinetic parameters. To develop a steady state glucose model, the Windows version of SAAM software (WinSAAM) was used. A 4-compartment model was adequate to comprehensively describe plasma glucose metabolism. The main model compartments consisted of propionate and plasma glucose. The time frame of the 480-min sampling period post-tracer glucose infusion allowed accurate quantification of glucose metabolism. The model estimated that glucose input from sources other than ruminal propionate decreased with MON, from 2.26 to 1.09 g/min postpartum. Gluconeogenesis, expressed as the propionate contribution to the plasma glucose pool, increased in cows fed MON (22 vs. 31%), whereas glucose oxidation, expressed as the glucose disposal rate, significantly decreased (1.67 vs. 0.92 g/min). In conclusion, MON may improve the energy status of transition cows by (1) improving the efficiency of propionate to produce glucose and (2) decreasing glucose oxidation in body tissues.     

Effects of somatotropin and substrates on patterns of liver metabolism in lactating dairy cattle.

Objectives of this study were to quantitate metabolite fluxes in ruminant liver and to delineate effects of recombinant bST on patterns of nutrient metabolism by liver. Nineteen multiparous cows ranging in previous lactational performance from 6400 to 13,500 kg per 305-d lactation were treated with either placebo or bST (40 mg/d) from wk 11 to 18 of lactation. Liver tissue was collected at slaughter. Tissue slices were incubated with various 14C-labeled substrates, and rates of conversion of label to CO2 and metabolites were measured. In vivo recombinant bST treatment increased in vitro conversion of [1-14C]propionate and [2-14C]acetate to glucose more than twofold. At 2.5 mM propionate, bST-treated cows converted propionate to glucose at 90% efficiency. Recombinant bST increased [14C]bicarbonate incorporation into glucose five-fold. Overall, bST treatment resulted in greater C flow from propionate and acetate through the TCA cycle. Acetate had only small effects on propionate metabolism and no effects on lactate plus pyruvate metabolism. Unexpectedly, propionate decreased acetate conversion to ketone bodies. Suggested mechanisms for this observation include depletion of coenzyme A and allosteric regulation of carnitine palmitoyltransferase I by methylmalonyl-coenzyme A formed from propionate. In summary, bST treatment resulted in increased rates of gluconeogenesis and oxidation in liver in support of lactation.     

Dose-response effects of intrauminal infusion of propionate on feeding behavior of lactating cows in early or midlactation

The objective of this experiment was to evaluate whether dose-response effects of intraruminal infusion of propionate on feeding behavior and dry matter intake (DMI) differ by stage of lactation. Six cows in early lactation (EL) and six cows in midlactation (ML) were assigned to blocks in a duplicated 6 × 6 Latin square design experiment. Treatments were mixtures of sodium propionate and sodium acetate containing sodium propionate at 0, 20, 40, 60, 80, and 100% of total volatile fatty acids (VFA), infused into the rumen continuously for 18 h starting 6 h before feeding at a rate of 21.7 mmol of sodium VFA/min. All cows were ruminally cannulated prior to the experiment. The diet was formulated to contain 30% NDF, and dry cracked corn was the major source of starch. We hypothesized that hypophagic effects of propionate infusion were greater for EL compared with ML because of greater plasma concentration of nonesterified fatty acids (275 vs. 76 μMeq/L) and expected greater basal oxidative metabolism in the liver for EL compared to ML. Propionate infusion decreased DMI for EL and ML, but a quadratic effect of propionate infusion was observed for ML but not EL. This indicated a greater marginal reduction in DMI at higher doses of propionate for ML compared to EL, contrary to our hypothesis. Propionate infusion decreased meal size similarly for both stages of lactation, but linearly increased intermeal interval for ML but not EL. We speculate that lower milk yield for ML compared with EL (30.8 vs. 42.0 kg/d) decreased glucose demand by the mammary gland and increased the proportion of infused propionate oxidized in the liver for ML compared to EL.     

异黄酮代谢动力学研究

大豆异黄酮是大豆生长中形成的一类次生代谢产物,是大豆中主要的多酚化合物。异黄酮主要来源于豆类食物,已证实具有预防退行性疾病,例如癌症、心血管疾病、糖尿病、高脂血症等。为了深入探讨异黄酮的生物学效应与生物代谢之间的关系,我们利用动物实验进行了小鼠血液中异黄酮的峰值浓度(Cmax)、峰值时间(Tmax)、曲线下面积(AUC)、消除半衰期(t1/2)以及粪便排泄量等代谢动力学参数的测算。本实验用甲醇溶解异黄酮和紫外分光光度计测定取得了较好效果;小鼠灌胃(i.g.)10mg/kgbw和20mg/kgbw两种剂量,结果显示低剂量组的血液含量0.65μg/ml;高剂量组的血液含量为0.75μg/ml,但是出现了首过消除现象;两组的消除半衰期差异不大;24h小鼠的粪便排泄量为总摄入量的19.87%,小于吸收排泄量11%,因此可得异黄酮的排泄主要是经过尿液排泄,经肝肠循环为次要排泄途径。     

Metabolism of propionate, glucose, and carbon dioxide as affected by exogenous glucose in dairy cows at energy equilibrium

In vivo kinetic techniques were used to quantify changes in metabolism of propionate, glucose, and blood CO2 when glucose was infused intravenously at 0, 342, or 737 g/d into four lactating cows. Neither production of milk or milk fat nor composition of milk was changed. Production of milk protein increased for the high glucose treatment. Isotope dilution data were used to calculate irreversible losses of rumen propionate, plasma glucose, and blood CO2 and to determine a unique solution for flux of C in this three-pool system. Irreversible losses of propionate and CO2 were not changed. Infusions of glucose increased irreversible loss of glucose in proportion to amounts infused, thus indicating there was no change in endogenous production of glucose. For the control, 52% of the C flux of blood glucose was derived directly from rumen propionate and another 26% came from other gluconeogenic substrates. Flux of C into glucose from exogenous sources increased in proportion to amounts of glucose infused. Flux of C from rumen propionate remained constant. The rate of C leaving the glucose pool, other than as CO2, tended to increase with infusion of glucose, and oxidation of glucose tended to increase for the high glucose treatment. High producing cows adjusted to increased exogenous glucose by increasing glucose utilization and without decreasing endogenous glucose production.     

Net volatile fatty acid absorption in nonlactating holstein cows

Net absorption of volatile fatty acids was measured in four nonlactating Holstein cows fed orchardgrass-clover silage ad libitum and 50 g trace mineralized salt daily. Cows ranged in age from 2 to 4 yr and in body weight from 326 to 525 kg. Portal blood flow and volatile fatty acid concentrations of portal and arterial plasma were determined at 30-min (three cows) or 90-min (one cow) intervals for about 12 h. Mean portal blood flow was 836 liters/h. Mean volatile fatty acid concentrations of portal plasma and differences of portal-arterial concentrations were (mM): acetate 2.00, .67; propionate .264, .228; isobutyrate .022, .017; n-butyrate .057, .038; 2-methylbutyrate .017, .014; 3-methylbutyrate .007, .005; and n-valerate .012, .008. Mean net volatile fatty acid absorption was 682 mmol/h. Acetate and propionate accounted for 91% of net volatile fatty acid absorption on a molar basis and 85% on an energy basis. Net energy absorbed as volatile fatty acid was 5.43 Mcal/cow per day, which was about 35% of calculated metabolizable energy intake. Portal blood flow was maximal 1.5 h postfeeding, and net volatile fatty acid absorption was maximal 2.5 h postfeeding.     

Effect of lipopolysaccharide on indices of peripheral and hepatic metabolism in lactating cows

Four multiparous lactating cows (175 to 220 d in milk [DIM]) were used in a 4 x 4 Latin square design to assess the effects of four doses (0.0, 0.5, 1.0, and 1.5 microg/kg of body weight) of lipopolysaccharide (LPS; Escherichia coli 0111:B4) on performance and plasma metabolite and hormone concentrations. In addition, effects of immune activation on in vitro hepatic metabolic capacity were evaluated in 12 multiparous lactating cows (150 to 220 DIM) infused with 0 (n = 6), 1.0 (n = 4) or 2.0 (n = 2) microg of LPS/kg. Milk production and DMI decreased linearly with LPS dose for 24 h after LPS infusion. Overall mean plasma tumor necrosis factor-alpha, insulin, glucagon, and cortisol concentrations increased linearly with LPS dose, and plasma beta-hydroxybutyrate decreased linearly by dose after LPS infusion. Infusion of LPS decreased the insulin:glucagon molar ratio, but did not affect plasma concentrations of growth hormone, insulin-like growth factor-1, leptin, or L-(+)-lactate. Plasma concentrations of glucose tended to increase initially and subsequently decrease, and there was a quadratic tendency for increased plasma nonesterified fatty acid concentrations after LPS administration. In vitro hepatic capacity for conversion of [1-(14)C]L-(+)-lactate and [1-(14)C]palmitate, but not [1-(14)C]propionate or [1-(14)C]L-alanine, to CO2 increased after LPS administration. Hepatic capacity to convert [1-(14)C]propionate to glucose tended to increase, but neither esterification nor the conversion of palmitate to acid soluble products was altered by LPS. The LPS infusion resulted in significant changes of endocrine mediators responsible for regulation of energy metabolism of lactating cows and tended to alter subsequent in vitro hepatic metabolic capacity.     

Characterization of bovine glucose transporter 1 kinetics and substrate specificities in Xenopus oocytes

Glucose is an essential substrate for lactose synthesis and an important energy source in milk production. Glucose uptake in the mammary gland, therefore, plays a critical role in milk synthesis. Facilitative glucose transporters (GLUT) mediate glucose uptake in the mammary gland. Glucose transporter 1 (GLUT1) is the major facilitative glucose transporter expressed in the bovine mammary gland and has been shown to localize to the basolateral membrane of mammary epithelial cells. Glucose transporter 1 is, therefore, thought to play a major role in glucose uptake during lactation. The objective of this study was to determine the transport kinetic properties and substrate specificity of bovine GLUT1 using the Xenopus oocyte model. Bovine GLUT1 (bGLUT1) was expressed in Xenopus oocytes by microinjection of in vitro transcribed cRNA and was found to be localized to the plasma membrane, which resulted in increased glucose uptake. This bGLUT1-mediated glucose uptake was dramatically inhibited by specific facilitative glucose transport inhibitors, cytochalasin B, and phloretin. Kinetic analysis of bovine and human GLUT1 was conducted under zero-trans conditions using radio-labeled 2-deoxy-D-glucose and the principles of Michaelis-Menten kinetics. Bovine GLUT1 exhibited a Michaelis constant (K(m)) of 9.8 ± 3.0mM for 2-deoxy-d-glucose, similar to 11.7 ± 3.7 mM for human GLUT1. Transport by bGLUT1 was inhibited by mannose and galactose, but not fructose, indicating that bGLUT1 may also be able to transport mannose and galactose. Our data provides functional insight into the transport properties of bGLUT1 in taking up glucose across mammary epithelial cells for milk synthesis.     

Evaluation of glucose dose on intravenous glucose tolerance test traits in Holstein-Friesian heifers

Glucose metabolism in dairy and beef cattle has received considerable attention because balanced blood glucose is essential for numerous processes, such as milk production and general health. The glucose tolerance test measures the ability of an organism to regulate blood glucose levels. Glucose half-life time (GHLT) has high heritability and could serve as a potential parameter to breed for metabolic resistance. However, studies focusing on identification of an adequate glucose dose have not yet been conducted in cattle. The objective of this study was to analyze the effect of 5 different glucose doses (0.5, 1, 1.5, 2, and 3 g/kg of body weight^0.75) on intravenous glucose tolerance test (ivGTT) traits and insulin responses in nongestating heifers. A total of 150 tests were performed in 30 Holstein-Friesian heifers aged 13 to 15 mo. Blood samples were obtained every 7 min after glucose injection until min 63. Glucose traits and insulin parameters included blood serum glucose and insulin concentration at min 0 (basal concentration), min 7 to 21 (peak glucose and insulin concentration), and min 63 (last sampling) relative to glucose administration, glucose and insulin area under the curve (GAUC and IAUC), and GHLT estimated between min 14 and 42. Serum glucose and insulin concentrations were measured according to the hexokinase colorimetric method and radioimmunoassay, respectively. Generalized linear mixed model was used to test for significant differences in ivGTT traits, insulin responses, and glucose elimination rates (k) over time at different glucose doses. Maximum glucose and insulin concentrations at min 63 increased with higher glucose doses. Significantly lower GHLT were obtained at increasing glucose doses, whereas GAUC and IAUC were significantly higher at increasing doses. The k values were affected by glucose dose and by time interval. Glucose dose greatly affected most ivGTT traits, insulin responses, and glucose elimination rates. Therefore, researchers should standardize their methods to achieve repeatable results and use the same time points for GHLT calculation. Higher glucose doses (≥1.5 g/kg of body weight^0.75) triggered glucose concentrations above the glucose renal threshold during the initial 42 min, whereas the lowest glucose concentration failed to induce a maximum insulin response. Further research is necessary to determine an adequate dose inducing maximum insulin responses with minimum renal glucose losses.     

Effects of chromium propionate on response to an intravenous glucose tolerance test in growing Holstein heifers

To test the effect of chromium propionate on glucose utilization in growing dairy heifers, 0, 5, 10, or 15 mg of chromium/d were fed to 20 Holstein heifers of 11 to 14 mo of age, in a replicated Latin square. A 2-wk adaptation period was followed by 4 periods of 2 wk each with a 2-wk flush out period between treatments. Treatments were allotted to periods in a design balanced for potential carryover effects. Chromium propionate was fed in 0.25 kg/d of ground corn individually. After 14 d on each treatment, animals were fitted with an indwelling jugular catheter, and an intravenous glucose tolerance test was conducted the following morning. Body weights increased throughout the experiment, but weights and condition scores were unaffected by treatment. Chromium supplementation increased basal glucose and decreased basal insulin and nonesterified fatty acids (NEFA) in serum in a dose-dependent, quadratic manner. Chromium increased glucose clearance rate as measured by half-life, time to nadir, and area under the curve. Over all periods, insulin concentrations tended to be lower in treated animals whereas clearance rates were unchanged. Serum NEFA levels were negatively correlated with glucose, such that treated animals with increased glucose had lower NEFA overall. There was an apparent long-term effect of chromium, because heifers in period 4 on the control diet had reduced insulin concentrations than those in the other control periods. Chromium propionate may increase glucose utilization in growing dairy heifers.     

Effects of rumen or duodenal glucose infusions on intake in dairy cows fed fresh perennial ryegrass indoors

The aim of this study was to determine whether the intake of fresh highly digestible ryegrass could be limited by the total amount of energy absorbed. Moreover, it investigated whether the limitation was more specific to energy absorbed as volatile fatty acids in the rumen compared with energy absorbed in the lower gastrointestinal tract. Four treatments were compared: infusion of 1.25 kg of glucose into the rumen (R1.25), infusion of 2.5 kg of glucose into the rumen (R2.5), infusion of 1.5 kg of glucose into the duodenum (D1.5), and a control treatment consisting of water and salts. Treatments R2.5 and D1.5 were assumed to supply about 16.5 MJ of net energy for lactation. All treatments consisted of 2 infusions, one into the rumen and the other into the duodenum, with one of these infusions being a control. All infused solutions were isoosmotic with osmolarities around 340 and 330 mmol/L for rumen and duodenum, respectively. Treatments were compared using 4 dairy cows in mid lactation according to a 4 × 4 Latin square design replicated twice during 8 periods of 7 d each. Cows were housed in tie stalls and fed ad libitum with fresh perennial ryegrass cut every morning during the spring at 28 d of regrowth. Intake and feeding behavior were measured, as well as concentrations of ruminal fermentation products and some blood metabolites. The pepsin-cellulase organic matter digestibility of the offered herbage averaged 0.76 ± 0.011. The average dry matter intake of herbage was 15.5 ± 0.52 kg/d. The glucose infusions decreased dry matter intake by 0.95 kg/d compared with the control, but had the same satiating effect regardless of site or dose of infusion. The average concentration of volatile fatty acids in rumen fluid was 97.9 ± 2.03 mmol/L and the molar proportion of propionate was 21.6 ± 0.19 mmol/100 mmol. Glucose infusions into the rumen led to a decrease in the molar proportions of acetate from 64.4 on the control treatment to 60.9 mmol/100 mmol on R2.5 and increased the molar proportions of butyrate from 10.2 (control) to 13.5 mmol/100 mmol on R2.5, and minor acids (valerate and caproate), from 1.27 (control) to 2.54 mmol/100 mmol on R2.5, proportionally to the dose infused. These results suggested that energy nutrients can limit intake in dairy cows fed high-digestibility ryegrass and that butyrate and minor acids would have a limited satiating effect compared with propionate.     

Metabolism of dairy cows as affected by prepartum dietary carbohydrate source and supplementation with chromium throughout the periparturient period

Holstein cows (n = 72) entering second or later lactation were used to determine whether metabolic indices and hepatic capacities for oxidation and gluconeogenesis from propionate are affected by source of carbohydrate in the prepartum diet and chromium-l-methionine (Cr-Met) supplementation throughout the periparturient period. Cows were fed prepartum diets as total mixed rations with the concentrate portion based either on starch-based cereals [high nonfiber carbohydrate (NFC); 1.59 Mcal/kg of net energy for lactation (NE_L), 14.4% crude protein (CP), 40.3% NFC] or nonforage fiber sources (low NFC; 1.54 Mcal/kg of NE_L, 14.5% CP, 33.6% NFC) from 21 d before expected parturition until parturition. After parturition all cows were fed a common lactation total mixed ration (1.74 Mcal/kg of NE_L, 16.5% CP, 40.0% NFC). The Cr-Met was supplemented once daily via gelatin capsule at dosages of 0, 0.03, or 0.06 mg of Cr/kg of BW^0.75. Thus, treatments were in a 2 (carbohydrate source) × 3 (Cr-Met) factorial arrangement. There was no effect of prepartum carbohydrate source on pre- and postpartum plasma concentrations of glucose, nonesterified fatty acids (NEFA), β-hydroxybutyrate (BHBA), insulin, glucagon, or insulin to glucagon ratio. However, cows fed the low NFC diet during the prepartum period tended to have greater plasma NEFA and lower BHBA concentrations postpartum. Liver glycogen concentrations tended to be greater on d 1 postpartum for cows fed low NFC prepartum. Supplementing 0.03 mg/kg of BW^0.75 of Cr as Cr-Met increased prepartum plasma glucose and glucagon concentrations and tended to decrease prepartum plasma NEFA concentrations compared with either 0 or 0.06 mg of Cr/kg of BW^0.75. Postpartum plasma glucose concentrations decreased linearly and glucagon concentrations were increased quadratically by administering increasing amounts of Cr-Met. Supplementing Cr-Met did not affect prepartum plasma concentrations of insulin or BHBA, postpartum NEFA or BHBA, or liver composition. There was an interaction of prepartum carbohydrate source and Cr-Met supplementation such that in vitro hepatic conversion of [1-¹⁴C]propionate to both CO₂ and glucose was similar or increased when Cr-Met was supplemented to cows fed the low NFC diet but decreased when Cr-Met was supplemented to cows fed the high NFC diet. Insulin addition in vitro did not affect hepatic metabolism of propionate on d 1 postpartum. Overall, both the NFC content of the prepartum diet and Cr-Met had only modest effects on metabolic indices in this experiment.     

The effect of short-term hyperammonaemia on milk synthesis in dairy cows

To test the hypothesis that ammonia detoxification in ruminants consumes amino acids to the detriment of milk protein production, we infused four lactating dairy cows with ammonium acetate or sodium acetate in switchback experiments. Plasma ammonia concentrations increased to 411 microm within 1 h of the start of infusion of ammonium acetate at 567 mmol/h. The rate constant for ammonia clearance from plasma was 0 x 054/min and the half-life was 12 x 9 min. Infusion at 567 mmol/h for 1 h followed by 1 h without infusion, repeated four times between am- and pm-milking, caused a decrease in feed intake. Compared with sodium acetate, continuous infusion of ammonium acetate at 360 mmol/h throughout an entire 10-h milking interval increased plasma ammonia concentrations to 193 microm and caused a 20% decrease in milk, protein and lactose production with no effect on percentage composition of milk or the yield of milk fat. Arterial concentrations of glucose and non-esterified fatty acids tended to increase; there was no effect on arterial acetate, beta-hydroxybutyrate or triacylglcerol, and branched-chain amino acids, Lys and Thr decreased. Mammary plasma flow, estimated by assuming 100% uptake/output of Phe+Tyr, was significantly correlated with milk yield. Mammary uptakes of acetate tended to be reduced by hyperammonaemia, but uptakes of other energy metabolites and amino acids were not affected. Thus, while an increase in amino acid consumption during hyperammonaemia was apparent from the drop in circulating concentrations of Leu, Ile, Val, Lys and Thr, there was no evidence to support the hypothesis that milk yield is affected by the lower concentrations. An ammonia-induced depression in feed intake may have caused the decrease in milk synthesis.     

Relationship of portal-drained viscera and liver net flux of glucose, lactate, volatile fatty acids, and nitrogen metabolites to milk production in the ewe

The objectives of this study were, first, to determine the relationship between hepatic glucose release and milk production and, second, to determine the relationship between net hepatic uptake of gluconeogenic precursors and milk production. Nine multiparous ewes were individually penned and fed an alfalfa hay-based diet for ad libitum intake. Catheters were surgically placed in the portal vein, a branch of the hepatic vein, a mesenteric vein, and the abdominal aorta. Metabolite fluxes across the portal-drained viscera and liver were subsequently measured at 1, 3, 6, and 10 wk after parturition. Net hepatic glucose release, net hepatic lactate uptake, and net hepatic propionate uptake increased with increased milk production. Hepatic oxygen consumption increased with increased net hepatic glucose release. Net hepatic glucose release increased with increased hepatic propionate uptake and tended to increase with increases in metabolized amino acid and lactate uptakes. The observed increases in oxygen consumption by the portal-drained viscera with increased milk production were probably the result of increased nutrient flux. Increased hepatic oxygen consumption with increased milk production was probably due to increased glucose and urea synthesis.     

Effect of indomethacin administration on glucose homeostasis and pancreatic hormones in lactating goats

To determine glucogenic and hormonal responses in ruminants to indomethacin, a prostaglandin synthetase inhibitor, four lactating Toggenburg goats were used in a crossover design. Fifteen milligrams of indomethacin or 3 ml of saline were injected subcutaneously twice daily with propionate infused intrajugularly at a rate of 2 mM/min for 75 min as a challenge. Plasma glucose concentrations were increased by indomethacin injections. Plasma concentrations of insulin, glucagon, and 6-keto-prostaglandin F1 alpha were not affected by indomethacin injections. Propionate infusion elevated plasma glucose, insulin, and glucagon concentrations. A decreased insulin release in response to propionate challenge was observed with indomethacin injections.     

Ruminal and intermediary metabolism of propylene glycol in lactating Holstein cows

Four lactating Holstein cows fitted with ruminal cannulas and permanent indwelling catheters in the mesenteric artery, mesenteric vein, hepatic portal vein, and hepatic vein were used in a cross-over design to study the metabolism of propylene glycol (PG). Each cow received 2 treatments: control (no infusion) and infusion of 650 g of PG into the rumen at the time of the morning feeding. Propylene glycol was infused on the day of sampling only. Samples of arterial, portal, and hepatic blood as well as ruminal fluid were obtained at 0.5 h before feeding and at 0.5, 1.5, 2.5, 3.5, 5, 7, 9, and 11 h after feeding. Infusion of PG did not affect ruminal pH or the total concentration of ruminal volatile fatty acids, but did decrease the molar proportion of ruminal acetate. The ruminal concentrations of PG, propanol, and propanal as well as the molar proportion of propionate increased with PG infusion. The plasma concentrations of PG, ethanol, propanol, propanal, glucose, l-lactate, propionate, and insulin increased with PG and the plasma concentrations of acetate and β-hydroxybutyrate decreased. The net portal flux of PG, propanol, and propanal increased with PG. The hepatic uptake of PG was equivalent to 19% of the intraruminal dose. When cows were dosed with PG, the hepatic extraction of PG was between 0 and 10% depending on the plasma concentration of PG, explaining the slow decrease in arterial PG. The increased net hepatic flux of l-lactate with PG could account for the entire hepatic uptake of PG, which suggests that the primary hepatic pathway for PG is oxidation to l-lactate. The hepatic uptake of propanol increased with PG, but no effects of PG on the net hepatic and net splanchnic flux of glucose were observed. Despite no effect of PG on net portal flux and net hepatic flux of propionate, the net splanchnic flux of propionate increased and the data suggest that propionate produced from hepatic metabolism of propanol is partly released to the blood. The data suggest that PG affects metabolism of the cows by 2 modes of action: 1) increased supply of l-lactate and propionate to gluconeogenesis and 2) insulin resistance of peripheral tissues induced by increased concentrations of PG and propanol as well as a decreased ratio of ketogenic to glucogenic metabolites in arterial blood plasma.     

Effects of slow-release insulin on production,liver triglyceride,and metabolic profiles of Holsteins in early lactation

The objective of this experiment was to determine whether there is a dose of slow-release insulin (SRI) that decreases concentrations of plasma nonesterified fatty acids (NEFA) and liver triglyceride (TG) without decreasing plasma glucose concentration, dry matter intake (DMI), and milk yield. Forty-three Holsteins weighting 765 +/- 70 kg with body condition score of 3.29 +/- 0.25 (mean +/- SD) were fed for ad libitum consumption of the same diet from 2 wk before parturition through 6 d postpartum. Cows were blocked according to actual calving date and parity and then assigned randomly to intramuscular injection of a single dose of 0, 0.14, 0.29, or 0.43 IU of SRI per kilogram of body weight (BW) on d 3 postpartum. On the day of injection, cows were fed hourly to minimize fluctuations in blood hormones and metabolites due to feed intake pattern. Blood samples were collected via jugular catheter every hour from 0 to 24 h and every 6 h from 24 to 48 h postinjection. Pre- and postinjection period liver samples were taken on d 2 and 5 postpartum. One cow injected with 0.29 and two cows injected with 0.43 IU of SRI per kilogram of BW could not complete the trial due to severe hypoglycemia (< 20 mg/dl). Both DMI and milk yield during d 3 to 5 postpartum tended to increase quadratically by increasing dose of SRI. Concentrations of serum insulin and glucagon increased linearly, concentration of plasma glucose decreased linearly, and concentrations of plasma NEFA and beta-hydroxybutyrate decreased quadratically from 0 to 24 h postinjection by increasing dose of SRI. Serum insulin concentrations remained higher in cows injected with SRI (CISRI) than in cows injected with sterile water (CISW; 0 IU of SRI/kg of BW), the quadratic effect of SRI on plasma NEFA concentration continued, and the linear effect of SRI on plasma glucose concentration diminished from 24 to 48 h postinjection. Concentration of hepatic TG for CISRI tended to be lower than for CISW, and increasing dose of SRI quadratically decreased hepatic accumulation of TG. Increasing dose of SRI tended to increase concentration of hepatic glycogen (GLY) quadratically and decreased the ratio of TG to GLY quadratically. In conclusion, a low dose of SRI (0.14 IU/kg of BW) could be considered for prophylactic use against hepatic lipidosis and ketosis.     

Effects of volatile fatty acids on propionate metabolism and gluconeogenesis in caprine hepatocytes

Isolated caprine hepatocytes were incubated with fatty acids of various chain lengths. Short-chain fatty acids effects on rates of gluconeogenesis and oxidation from [2-14C]propionate were determined. Additions of glucose (2.5 mM) had no effect on hepatic [2-14C]propionate metabolism in the presence and absence of amino acids. A complete mixture of amino acids increased label incorporation from [2-14C]propionate into [14C]glucose by 22%. Butyrate inhibited [2-14C]propionate metabolism and increased the apparent Michaelis constant for [2-14C]propionate incorporation into [14C]glucose from 2.4 +/- 1.5 to 5.6 +/- .9 mM. Butyrate's effects on propionate were similar in the presence and absence of L-carnitine (1 mM). Isobutyrate, 2-methylbutyrate, and valerate (1.25 mM) had no effect on [14C]glucose production but decreased 14CO2 production to 57, 61, and 54% of the control [2-14C]propionate (1.25 mM). This inhibition on 14CO2 production was not competitive. Isovalerate had no effect on either [2-14C]propionate incorporation into glucose or CO2. An increase in ratio of [14C]glucose to 14CO2 from [2-14C]propionate demonstrated that short-chain fatty acids other than butyrate do not inhibit gluconeogenesis from propionate. In addition, fatty acids that generate a net synthesis of intracellular oxaloacetate may partition propionate carbons toward gluconeogenic rather than oxidative pathways in goat hepatocytes.