Quantifying energy expenditure in Göttingen Minipigs with the 13C-bicarbonate method under basal and drug-treated conditions.

Effective treatments of obesity focusing on energy expenditure (EE) are needed. To evaluate future EE-modulating drug candidates, appropriate animal models and methods to assess EE are needed. This study aimed to evaluate the stable isotope 13C-bicarbonate method (13C-BM) for estimating EE in Göttingen minipigs under basal and drug-treated conditions. Four experiments (Expt.1-4) were conducted to assess: 1) the 13C-BM reproducibility using breath sample collection (n = 8), on two consecutive days, 2) the effect of two dose levels (5 and 10 mg/kg body weight (BW)) of the mitochondrial uncoupler dinitrophenol (DNP) in a crossover design (n = 8), 3) sampling method agreement; blood vs. exhaled air (n = 6) and 4) 13C-BM using constant isotope infusion compared with indirect calorimetry (IC) (n = 3). Results correlated significantly (p < 0.001) between days (Expt.1), with an average coefficient of variance of 5.4 ± 2.3%. Administration of 10 mg DNP/kg BW increased (p < 0.01) EE by 33.2 ± 6.4% (Expt.2). Results based on different sampling methods correlated significantly (p < 0.001) and EE increased after 10 mg DNP/kg BW (p < 0.05) in Expt.3. However, results based on blood sampling were significantly higher (p < 0.01) than those of exhaled air. No effect of DNP and significantly different EE results (p < 0.05) was observed in a limited number of animals, when constant isotope infusion and blood sampling was compared with IC (Expt.4). In conclusion, the 13C-BM is useful for investigating treatment effects on EE in minipigs. However, further validation under standardized conditions is needed to provide accurate estimates of the 13C recovery factor and respiratory quotient, both of decisive importance when using the 13C-BM.

Measurement of plasma protein and whole body protein metabolism using [15N]glycine in a young adult man - a pilot study.

A novel simplified method is presented for the estimation of the metabolism of plasma proteins (albumin, fibrinogen, α, ß and γ-globulin, glycoprotein) with regard to the whole body protein metabolism in a young male volunteer (22 years, 81 kg body mass). This method is based on multiple oral administration of [15N]glycine followed by measurement of 15N in plasma proteins, total free amino acids, urea and excreted urinary N. The fractional synthesis rate of albumin was estimated to 6.8 % d-1 based on amino acids and 3.3 % d-1 based on urea, respectively. The fractional synthesis rate of the other plasma proteins ranged from 4.3 % d-1 (γ-globulin) to 26.4 % d-1 (α-globulin, fibrinogen). We conclude that the simplified approach using [15N]glycine provides results which are similar to results based on the simultaneously applied 131I-human serum albumin technique as 'gold standard' and to those reported in literature. The compartmental analysis considering comprehensive tracer kinetic data ensures reliable data treatment and enables statistical evaluation. The analytical effort is minimal because the 15N enrichment of plasma protein after chemical digestion may be directly used. Therefore, the novel stable isotope 15N method is suitable for studies in clinical and nutritional research and practice.

In vitro application of carbonic anhydrase to accelerate the equilibration of 18O between H2O and CO2 for the rapid measurement of 18O/16O isotope ratios in aqueous samples.

A novel method of the accelerated equilibration of 18O between CO2 and H2O for the measurement of the 18O/16O isotope ratios in aqueous samples with natural isotope abundances is presented. This rapid equilibrium method is based on the in vitro application of the enzyme carbonic anhydrase (CA). The CA from bovine erythrocytes was adsorptively fixed to 3-mm glass beads with an etched surface. After the addition of this carrier-fixed CA catalyst to the water sample, the isotope equilibrium was already reached after 1 h. The previously used non-catalysed 18O isotope exchange in water samples needs about 24 h. Whole blood samples also showed fast 18O isotope equilibration, which definitely results from the native presence of CA in erythrocytes. By shortening the time for sample preparation, the CA catalysed technique can significantly increase the throughput of the samples to be measured, and also 18O and 2H measurement by means of isotope ratio mass spectrometry (IRMS) may be synchronized. The 2H and 18O sample preparation can be performed in the same reaction vessel because cross-effects at the simultaneous use of Pt and CA catalysts do not occur.

A novel doubly labelled 13C, 15N amino acid method for measuring energy and protein metabolism in man.

A novel doubly [1-13C, α-15NH2]-labelled amino acid method (DLAAM) is presented for the determination of the CO2 production (RCO2) and energy expenditure in humans. This method is based on the simultaneous administration of [1-13C]glycine and [15N]glycine followed by the measurement of excretion kinetics of breath 13CO2 and urinary 15N. The basic idea of the DLAAM is that the unknown 13C recovery RF(13C) of the 1-13C amino acid, essential for the calculation of the net CO2 production, can be approximated by the easily measureable 15N recovery RF(15N) of the α-15NH2 labelled amino acid. In four healthy adult men (76-97 kg) the DLAAM was tested parallel to the IC and in one man (74 kg) parallel to the DLWM. Using the approximation RF(13C) ≈ RF(15N) the RCO2 (in l CO2 d-1) was calculated to 387.0 ± 30.3 (DLAAM) vs. 382.8 ± 22.6. (IC). The Bland-Altman plot shows that the difference between the DLAAM and IC of individual RCO2 is within the 95 % confidence interval (mean ± 2 SD): +4.3 ± 37.5 l CO2 d-1. We conclude that the DLAAM and IC may be used interchangeably. The physical activity level (PAL) was calculated based on the DLAAM vs. DLWM to about 1.5.

Breath water-based doubly labelled water method for the noninvasive determination of CO2 production and energy expenditure in mice.

We explored a novel doubly labelled water (DLW) method based on breath water (BW-DLW) in mice to determine whole body CO2 production and energy expenditure noninvasively. The BW-DLW method was compared to the DLW based on blood plasma. Mice (n = 11, 43.5 ± 4.6 g body mass (BM)) were administered orally a single bolus of doubly labelled water (1.2 g H218O kg BM-1 and 0.4 g 2H2O kg BM-1, 99 atom% (AP) 18O or 2H). To sample breath water, the mice were placed into a respiration vessel. The exhaled water vapour was condensed in a cold-trap. The isotope enrichments of breath water were compared with plasma samples. The 2H/1H and 18O/16O isotope ratios were measured by means of isotope ratio mass spectrometry. The CO2 production (RCO2) was calculated from the 2H and 18O enrichments in breath water and plasma over 5 days. The isotope enrichments of breath water vs. plasma were correlated (R2 = 0.89 for 2H and 0.95 for 18O) linearly. The RCO2 determined based on breath water and plasma was not different (113.2 ± 12.7 vs. 111.4 ± 11.0 mmol d-1), respectively. In conclusion, the novel BW-DLW method is appropriate to obtain reliable estimates of RCO2 avoiding blood sampling.

The ¹³C bicarbonate method: an inverse end product method for measuring CO2 production and energy expenditure.

We reconsider the principle of the (13)C bicarbonate (NaH(13)CO3) method ((13)C-BM) for the determination of the CO2 production to obtain an estimate of energy expenditure (EE). Its mathematical concept based on a three-compartmental model is related to the [(15)N]glycine end product method. The CO2 production calculated by the (13)C-BM, RaCO2((13)C) is compared to the result from the indirect calorimetry, RCO2(IC). In an interspecies comparison (dog, goat, horse, cattle, children, adult human; body mass ranging from 15 to 350 kg, resting and fasting conditions) we found an excellent correlation between the results of (13)C-BM and IC with RCO2(IC) = 0.703 × RaCO2((13)C), (R(2) = 0.99). The slope of this correlation corresponds to the fractional (13)C recovery (RF((13)C)) of (13)C in breath CO2 after administration of NaH(13)CO3. Significant increase in RF((13)C) was found in physically active dogs (0.95 ± 0.14; n = 5) vs. resting dogs (0.71 ± 0.10, n = 17; p = .015). The (13)C recovery in young bulls was greater in blood CO2 (0.81 ± 0.05) vs. breath CO2 (0.73 ± 0.05, n = 12, p < .001) and in ponies with oral (0.76 ± 0.03, n = 8) vs. intravenous administration of NaH(13)CO3 (0.69 ± 0.07; n = 8; p = .026). We suggest considering the (13)C-BM as a 'stand-alone' method to provide information on the total CO2 production as an index of EE.

The oral [(13)C]bicarbonate technique for measurement of short-term energy expenditure of sled dogs and their physiological response to diets with different fat:carbohydrate ratios.

The oral [(13)C]bicarbonate technique (o(13)CBT) was assessed for the determination of short-term energy expenditure (EE) under field conditions. A total of eight Alaskan huskies were fed two experimental diets in a cross-over experiment including two periods of 3 weeks. Effects of diets on EE, apparent total tract digestibility (ATTD) and on plasma hormones, blood lactate and glucose were furthermore investigated. The percentages of metabolisable energy derived from protein (P), fat (F) and carbohydrates (C) were 26:58:16 in the PFC diet and 24:75:1 in the PF diet. Measurements of EE were performed in the post-absorptive state during rest. Blood samples were collected during rest and exercise and ATTD was determined after days with rest and with exercise. EE was higher (P < 0·01) in period 2 than in period 1 (68 v. 48 kJ/kg body weight(0·75) per h). The ATTD of organic matter, crude protein and crude fat was higher (P < 0·01) in the PF diet compared with the PFC diet, and lower (P < 0·01) for total carbohydrates. Exercise did not affect ATTD. Higher (P < 0·01) insulin-like growth factor 1 and leptin concentrations were measured when fed the PF diet compared with the PFC diet. Concentrations of insulin decreased (P < 0·01), whereas cortisol and ghrelin increased (P < 0·05), after exercise. There was no effect of diet on blood lactate and glucose, but higher (P < 0·001) lactate concentrations were measured in period 1 than in period 2. The results suggest that the o(13)CBT can be used in the field to estimate short-term EE in dogs during resting conditions. Higher ATTD and energy density of the PF diet may be beneficial when energy requirements are high.

Evaluation of the oral (13)C-bicarbonate technique for measurements of energy expenditure in dogs before and after body weight reduction.

BACKGROUND: Overweight and obesity are the most common nutritional disorders in dogs and may lead to various secondary diseases and decreased lifespan. In obesity research, measurement of energy expenditure (EE) and determination of the energy requirements are essential. The objective with this study was to validate and evaluate the suitability of the oral (13)C-bicarbonate technique (o(13)CBT) for measuring EE in dog obesity studies. A further objective was to investigate the impact of body weight (BW) reduction and changes in body composition on the EE when measured under conditions corresponding to the basal metabolic rate (BMR). RESULTS: The EE in five privately owned, overweight dogs was measured simultaneously with the o(13)CBT and indirect calorimetry (IC) for comparison of the results. Two measurements per dog were performed under the same standardised conditions (i.e. fasted and resting state) at the start, and after completing a 12-week BW reduction program. Additionally, measurements of body composition by Dual-energy X-ray absorptiometry (DEXA) were conducted at the beginning and at the end of the BW reduction program. There were no differences in EE results obtained by the o(13)CBT and IC. Overweight and the BW reduction did not affect the estimates for the respiratory quotient (RQ) or the recovery factor for the (13)C-tracer (RF), both needed when using the o(13)CBT. The dogs lost 16% (SD ± 2.0) of their initial BW in reduced fat mass (P < 0.001), whereas fat free mass (FFM) remained unchanged. There was no effect of the BW reduction on the determined EE expressed in kJ/kg BW/d, or in kJ/kg BW(0.75)/d. However, EE was lower (P < 0.001) after the BW reduction program when expressed in relation to FFM (kJ/kg FFM/d). CONCLUSIONS: Results from the present study show that the o(13)CBT can be a used in obesity research to determine EE in fasted dogs and under resting conditions. Furthermore, the results suggest that the BMR does not change with reduced BW in overweight dogs as long as the FFM remains unchanged. This indicates that the BMR to maintain one gram of fat is equal to maintaining one gram of FFM in overweight dogs.

The oral (13)C-bicarbonate technique for estimation of energy expenditure in dogs: validation against indirect calorimetry.

To get more knowledge about the energy requirements of dogs and to formulate appropriate feeding guidelines, it is essential to determine their energy expenditure (EE) in a reliable and feasible way. In this study, the non-invasive oral stable isotope (13)C-bicarbonate technique (o(13)CBT) was validated against indirect calorimetry (IC) for the determination of CO2-production and EE in dogs. Eleven privately owned dogs were simultaneously measured with IC and the o(13)CBT after being fasted overnight. All dogs were measured twice on two separate days. For calculation, measurements were divided into two groups depending on dogs' behaviour during the measurement. Dogs of Group 1 (n = 17) were resting calmly in the chamber and dogs of Group 2 (n = 5) were more active. Mean heart rate was significantly higher in Group 2 (102 beats per minute [bpm]) than in Group 1 (77 bpm) (p < 0.001). Within groups, the CO2-production and EE [kJ d(-1) kg BW(-0.75)] estimated by the o(13)CBT or IC did not differ significantly (Group 1: [Formula: see text] = 368; EEIC = 363; Group 2: [Formula: see text] = 701; EEIC = 718). However, the estimated (13)C recovery factor (RF) for the estimation of CO2-production was significantly different between Groups 1 and 2 (0.72 and 0.94, respectively, p < 0.001). The respiratory quotient (RQ), which is needed for the estimation of EE, did not differ between groups. This study shows that the non-invasive o(13)CBT can be used for accurate estimation of the CO2-production rate and EE in resting dogs. A value of 0.77 can be applied as an estimate of the RQ in fasted dogs and 0.72 as an appropriate estimate for RF when dogs are resting calmly during the measurements.

Estimate of production of gaseous nitrogen in the human body based on (15)N analysis of breath N2 after administration of [(15)N2]urea.

After oral administration of [(15)N2]urea (1.5 mmol, 95 atom% (15)N), we found that breath N2 was significantly (15)N-labelled. The result suggests that molecular nitrogen in breath must be partly produced endogenously. Based on a metabolic model, the endogenous N2 production was estimated to be 0.40±0.25 mmol kg(-1) d(-1) or 2.9±1.8 % of the total (urinary and faecal) N excretion in fasted healthy subjects (n=4). In patients infected with Helicobacter pylori (n=5), the endogenous N2 production was increased to 1.24±0.59 mmol kg(-1) d(-1) or 9.0±4.3 % of the total N excretion compared to the healthy controls (p<0.05). We conclude that N balance and gas exchange measurements may be affected by endogenously produced nitrogen, especially in metabolic situations with elevated nitrosation, for instance in oxidative and nitrosative stress-related diseases such as H. pylori infections.

Studies of the protein and the energy metabolism in man during a wintering in Antarctica.

During the 29th Soviet Antarctic Expedition in Novolazarevskaya from March 1984 to March 1985, the protein and energy metabolisms were studied in six expeditioners from the German Democratic Republic. The investigations were carried out at the beginning of the expedition (May), during the polar night (July) and during the polar day (December). The effect of a special stress situation (sledge trek in April 1984) was investigated in one subject. The stable nitrogen isotope (15)N was used to study the protein metabolism. The assessment of the energy metabolism was based on the oxygen consumption, which was determined by means of a spirograph. In addition, the vital capacity, the breath minute volume, the blood pressure, etc. were measured. The following results were obtained: During the polar night, the utilisation of the dietary proteins and the whole body protein synthesis calculated by means of the (15)N excretion of the total nitrogen in urine were greater (73.6±0.9 % and 3.48±0.17 g protein d(-1) kg(-1), n=3) than the respective values during the polar day (69.7±1.2, p<0.05, n=3 and 3.05±0.07, p<0.05, n=3) and at the beginning of the expedition (69.6±1.4, p<0.02, n=5 and 2.81±0.09, p<0.01, n=5). The lowest values (58.0 % and 2.43 g protein d(-1) kg(-1)) were obtained in the subject after the trek. The resting metabolic rate (in kJ d(-1) m(-2)) was decreased during the polar night (45.6±5.0, n=4) in comparison with the polar day (61.5±11.3, n=3) and the beginning of the expedition (52.3±9.6, n=4) with p<0.01 in both cases.

Tracer kinetics and metabolic models in medicine.

In the present paper, a survey of methods applied to the interpretation and evaluation of tracer kinetic data is given. For their mathematical description, both compartmental and non-compartmental models, such as the modified model of Sprinson and Rittenberg, the San Pietro-Rittenberg model, two models of the albumin metabolism and a 10-pool model of the N and protein metabolism were used. By means of single or multiple pulse, infusion and priming techniques, the N and protein metabolism in various metabolic states (e.g. healthy man, pathological and stress conditions, therapeutic treatments) were studied.

Intestinal glucose absorption but not endogenous glucose production differs between colostrum- and formula-fed neonatal calves.

Glucose supply markedly changes during the transition to extrauterine life. In this study, we investigated diet effects on glucose metabolism in neonatal calves. Calves were fed colostrum (C; n = 7) or milk-based formula (F; n = 7) with similar nutrient content up to d 4 of life. Blood plasma samples were taken daily before feeding and 2 h after feeding on d 4 to measure glucose, lactate, nonesterified fatty acids, protein, urea, insulin, glucagon, and cortisol concentrations. On d 2, additional blood samples were taken to measure glucose first-pass uptake (FPU) and turnover by oral [U-(13)C]-glucose and i.v. [6,6-(2)H(2)]-glucose infusion. On d 3, endogenous glucose production and gluconeogenesis were determined by i.v. [U-(13)C]-glucose and oral deuterated water administration after overnight feed deprivation. Liver tissue was obtained 2 h after feeding on d 4 and glycogen concentration and activities and mRNA abundance of gluconeogenic enzymes were measured. Plasma glucose and protein concentrations and hepatic glycogen concentration were higher (P < 0.05), whereas plasma urea, glucagon, and cortisol (d 2) concentrations as well as hepatic pyruvate carboxylase mRNA level and activity were lower (P < 0.05) in group C than in group F. Orally administered [U-(13)C]-glucose in blood was higher (P < 0.05) but FPU tended to be lower (P < 0.1) in group C than in group F. The improved glucose status in group C resulted from enhanced oral glucose absorption. Metabolic and endocrine changes pointed to elevated amino acid degradation in group F, presumably to provide substrates to meet energy requirements and to compensate for impaired oral glucose uptake.

Evaluation of the oral ¹³C-bicarbonate tracer technique for the estimation of CO2 production and energy expenditure in dogs during rest and physical activity.

For feeding of working dogs during their daily life, illness, routine jobs or sporting activities, an accurate determination of their nutritional requirements is essential to ensure their optimal health and performance. To predict the appropriate guidelines about how to feed dogs, it appears essential to determine the energy expenditure (EE) in a reliable and feasible way. In the present experiment, the non-invasive oral ¹³C-bicarbonate tracer technique (o¹³CT), i.e. collection of breath samples after oral administration of NaH¹³CO3, was used for the estimation of CO2 production and EE in dogs. Measurements were conducted during two days of rest, and during three days with 3 h of exercise per day. Average EE was 483 and 876 kJ kg⁻°·75 d⁻¹ during rest and exercise, respectively. The o¹³CT seems appropriate to use as a minimal restrictive and non-invasive method to obtain reliable estimates of EE in dogs at different activity levels under near natural conditions.

A simplified mass isotopomer approach to estimate gluconeogenesis rate in vivo using deuterium oxide.

We compare a new simplified (2)H enrichment mass isotopomer analysis (MIA) against the laborious hexamethylentetramine (HMT) method to quantify the contribution of gluconeogenesis (GNG) to total glucose production (GP) in calves. Both methods are based on the (2)H labeling of glucose after in vivo administration of deuterium oxide. The (2)H enrichments of plasma glucose at different C-H positions were measured as aldonitrile pentaacetate (AAc) and methyloxime-trimethylsilyl (MoxTMS) derivatives or HMT by gas chromatography/mass spectrometry (GC/MS). Two pre-ruminating fasted Holstein calves (51 kg body mass, BM, age 7 days) received two oral bolus doses of (2)H(2)O (10 g/kg BM, 70 atom% (2)H) at 7:00 h and 11:00 h after overnight food withdrawal. Blood samples for fractional GNG determination were collected at -24 and between 6 and 9 h after the first (2)H(2)O dose. The ratio of (2)H enrichments C5/C2 represents the contribution of GNG to GP. The (2)H enrichment at C2 was calculated based on the ion fragments at m/z 328 (C1-C6) - m/z 187 (C3-C6) of glucose AAc. The (2)H enrichment at C5 was approximated either by averaging the (2)H enrichment at C5-C6 using the ion fragment of glucose MoxTMS at m/z 205 or by conversion of the C5 of glucose into HMT. The fractional GNG calculated by the C5-C6 average (2)H enrichment method (41.4 +/- 6.9%) compared to the HMT method (34.3 +/- 11.4%) was not different (mean +/- SD, n = 6 replicates). In conclusion, GNG can be estimated with less laborious sample preparation by means of our new C5-C6 average (2)H enrichment method using AAc and MoxTMS glucose derivatives.

Temporary consumption of diet with unbalanced amino acid pattern affects long-lasting growth retardation correlated with oxidative stress response associated gene expression in juvenile pigs.

BACKGROUND & AIMS: The present study was conducted to study whether oxidative stress is the trigger of long-term physiological effects of temporary consumption of a soy protein isolate (SPI) based diet with an imbalanced amino acid pattern. MATERIAL AND METHODS: Hepatic expression of 19 genes that are involved in and co-regulated with oxidative stress response and showing diet-associated expression after chronic SPI feeding using quantitative RT-PCR, growth and liver composition were investigated in a model of protein-underfeeding juvenile pigs, which were fed a casein (CAS) based diet for four weeks subsequent to a four week consumption of an SPI diet in comparison with chronically CAS fed animals. RESULTS: Temporary feeding of SPI diet resulted in prolonged up-regulation of genes involved in oxidative/cellular stress response (glutathione-S-transferase, peptide methionine sulfoxide reductase, calnexin, organic anion transport polypeptide 2). Cluster analysis of gene expression data indicated persistent SPI-related co-regulation of the genes involved in stress response with genes involved in the regulation of protein biosynthesis and in neuronal signalling for at least four weeks after replacement of SPI by CAS. Gene expression data are negatively correlated with body weight and liver protein content. CONCLUSION: Significant association of oxidative stress responsiveness with growth retardation and liver composition underline the possible impact of diet-affected oxidative stress for long-lasting deleteriously metabolic consequences.

Studies on persisting effects of soy-based compared with amino acid-supplemented casein-based diet on protein metabolism and oxidative stress in juvenile pigs.

Juvenile growing pigs were studied to explore whether a soy-based diet can induce persistent physiological alterations, especially in protein and energy metabolism, nutrient oxidation and redox homeostasis. In former studies we have shown that in juvenile pigs chronically fed protein diets based on either casein (CAS) or soy protein isolate (SPI), the SPI diet significantly decreases growth rate and increases oxidative stress responsiveness as compared to CAS. In addition, here we show that chronic feeding of SPI vs. CAS diet decreases whole body protein synthesis (WBPS) (p = 0.007) and hepatic gene expression associated with protein synthesis. To study persistent SPI effects, a three-period feeding experiment was designed: In the test group 18 pigs received the CAS diet for 24 days (period 1), followed by 31 days on the SPI diet (period 2) and further 31 days on the CAS diet (period 3). In the control group 18 pigs were fed the CAS diet throughout the three periods (86 days). Temporary consumption of SPI diet results in persistent changes of protein metabolism and oxidative stress responsiveness. After switching back from SPI to CAS diet the decrease of WBPS of the test group vs. control group was of borderline significance (p = 0.061), transcript levels of hepatic gene expressions of leucine aminopeptidase, endopeptidase 24.16, glutathione-S-transferase and peptide methionine sulfoxide reductase were increased. In liver tissue, total glutathione was increased and thiobarbituric acid reactive substances were decreased in the test vs. control group. In conclusion, results suggest that SPI-induced changes in protein and amino acid metabolism as well as in redox homeostasis and antioxidative potential in growing pigs persist 4 weeks after the cessation of SPI feeding.

First-pass metabolism limits the intestinal absorption of enteral alpha-ketoglutarate in young pigs.

Our results in a previous study indicated that the portal absorption of intragastrically fed alpha-ketoglutarate (AKG) was limited in young pigs. Our aim was to quantify the net portal absorption, first-pass metabolism, and whole-body flux of enterally infused AKG. In study 1, we quantified the net portal nutrient absorption in young pigs (n = 9) given an intraduodenal infusion of milk replacer [10 mL/(kg . h)] and either saline (control) or 930 micromol/(kg . h) AKG for 4 h. In study 2, we quantified the luminal disappearance of a duodenal AKG bolus in young pigs (n = 7). In study 3, we quantified the whole-body kinetics of (13)C-AKG metabolism when infused either enterally (n = 9) or intravenously (n = 9) in young pigs. In study 1, when compared with the control group, enteral AKG infusion increased (P < 0.01) the arterial (13.8 +/- 1.7 vs. 27.4 +/- 3.6 micromol/L) and portal (22.0 +/- 1.4 vs. 64.6 +/- 5.9 micromol/L) AKG concentrations and the net portal absorption of AKG [19.7 +/- 2.8 vs. 95.2 +/- 12.0 micromol/(kg . h)]. The mean fractional portal appearance of enterally infused AKG was 10.23 +/- 1.3%. In study 2, the luminal disappearance of AKG was 663 micromol/(kg . h), representing 63% of the intraduodenal dose. In study 3, the whole-body (13)C-AKG flux [4685 +/- 666 vs. 801 +/- 67 micromol/(kg . h)] was higher (P < 0.05) when given enterally than intravenously, but (13)CO(2) recovery was not different (37.3 +/- 1.0 vs. 36.2 +/- 0.7%dose). The first-pass splanchnic (13)C-AKG utilization was approximately 80%, of which 30% was oxidized to (13)CO(2). We conclude that the intestinal absorption of AKG is limited in young pigs largely due to substantial first-pass gastrointestinal metabolism.

Intraduodenal infusion of alpha-ketoglutarate decreases whole body energy expenditure in growing pigs.

BACKGROUND AND AIMS: alpha-Ketoglutarate (AKG) has been suggested to play a particular role as an oxidative fuel for the gut, and thus may have a sparing function for fuels such as glutamate and aspartate. Using the pig model we aimed to quantify how the route of administration (intravenous, i.v.; intragastric, i.g.; intraduodenal, i.d.) affects AKG utilization, whole body energy expenditure (EE) and nutrient oxidation. METHODS: Pigs (15 kg) were supplied with a complete nutrient solution (NS) via catheters. To explore the metabolic effects of AKG, 1.0 g AKG kgBW(-1)d(-1) was infused simultaneously with the NS using either the i.d., i.v. or i.g. route. [1-(13)C]AKG (15 mg kgBW(-1)) was infused i.d., i.v. or i.g., respectively, for 3h. AKG utilization (AKG UTIL) was estimated as AKG UTIL=100-(13)C recovery (% of (13)C dose). (13)C recovery was calculated from the (13)C enrichment in breath CO(2) and the whole-body CO(2) production. RESULTS: AKG infusion and NS via the i.d. route resulted in a reduced AKG UTIL (40.1+/-6.7) as compared to the i.v. route (62.9+/-2.4, P<0.001) and i.g. route (62.3+/-1.6, P<0.001). The total EE was lower with the i.d. route of AKG and NS (745+/-68 kJkgBW(-0.62)d(-1)) as compared to the i.v. route (965+/-54 kJkgBW(-0.62)d(-1), P<0.005) and i.g. route (918+/-43 kJkgBW(-0.62)d(-1), P<0.005). Carbohydrate oxidation was increased with the i.d. route (38.2g+/-3.4 kgBW(-0.62)d(-1)) as compared to the i.v. route (27.8+/-2.9 gkgBW(-0.62)d(-1), P<0.08) and i.g. route (23.9+/-8.5 gkgBW(-0.62)d(-1), P<0.05). Fat oxidation was decreased (2.1+/-1.9 gkgBW(-0.62)d(-1); P<0.001) with the i.d. route as compared to the i.v. route (11.5+/-1.4 gkgBW(-0.62)d(-1), P<0.001) and i.g. route (11.9+/-3.1 gkgBW(-0.62)d(-1), P<0.001). CONCLUSIONS: The i.d. infusion of AKG in combination with the NS affected the whole body EE and nutrient oxidation, in comparison to that obtained with the i.v. and i.g. routes. It was concluded that the i.d. administration of AKG markedly controlled the nutrient partitioning in the oxidation processes. Finally, in contrary to the observations with glutamine or glutamate, a considerable percentage of the AKG infusion was retained in the body irrespective of the route of administration.