J. Anim Sci. 2007. 85:2517-2523. doi:10.2527/jas.2006-237
© 2007 American Society of Animal Science
Changes in small intestinal nutrient transport and barrier function after lipopolysaccharide exposure in two pig breeds1
D. M. Albin*,2,3,
J. E. Wubben
,2,
J. M. Rowlett,
K. A. Tappenden* and
R. A. Nowak,4
* Division of Nutritional Sciences, and
Department of Animal Sciences, University of Illinois, Urbana 61801
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Abstract
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Specific pig breeds with unique characteristics have been developed, and the current study sought to characterize some of these differences. Using modified Ussing chambers, electrophysiological mucosal transport of D-glucose, L-Gln, L-Pro, L-Arg, L-Thr, and glycylsarcosine was assessed in small intestinal tissues (duodenum, jejunum, ileum) taken from Yorkshire-based hybrid (BW = 142.4 ± 2.0 kg; mean age = 8 mo) and Meishan (BW = 65.8 ± 0.8 kg; mean age = 6 mo) female pigs after 4 h of lipopolysaccharide (LPS) exposure. Gilts were randomly assigned to control (saline infusion; n = 6 Yorkshires, n = 5 Meishans) or LPS (n = 7 Yorkshires, n = 5 Meishans) groups. Therefore, treatments were arranged in a 2 (breed) x 2 (LPS infusion) factorial. Four hours after infusions, pigs were euthanized, and intestinal segment samples were removed. Glucose transport in the ileum was decreased (P < 0.001) in Yorkshires with LPS but was increased (P < 0.001) by over 2-fold in Meishans with LPS. After LPS infusion, Pro transport was increased in duodenum (over 5-fold; P = 0.04) and ileum (over 10-fold; P < 0.001) of Meishans but was unaffected in Yorkshires. Arginine transport in the ileum of control Meishans was greater (P = 0.05) than Arg transport in control Yorkshires. Glycylsarcosine transport was greater (P = 0.02) in Meishans than Yorkshires (nearly 2-fold), regardless of LPS provision. Glycylsarcosine transport was increased (P = 0.003) over 2-fold by LPS, regardless of pig breed. Resistance (barrier function) was increased (P = 0.03) by LPS in Yorkshires but was unaffected in Meishans. The current study indicates that small intestinal function responded differently to LPS in Yorkshire and Meishan gilts and that these effects were nutrient- and segment-dependent.
Key Words: nutrient transport • barrier function • intestine • lipopolysaccharide • pig breed
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INTRODUCTION
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Humans began domesticating pigs about 9,000 yr ago, because they provided food and raw materials (such as hides), and recent evidence suggests that several domestication centers existed (Larson et al., 2005
). European breeds, such as Yorkshire, have been selected for thousands of years to improve their beneficial production traits. Chinese breeds, such as Meishan, are very prolific and are thought to tolerate disease better than European breeds (Clapperton et al., 2005). The various breeds were likely exposed to different rearing conditions for thousands of years. Indeed, a recent report using microsatellite markers has indicated that European and Chinese breeds have diverged into 2 distinct groups (or were initially drawn from 2 different pools; Fan et al., 2002). Thus, it is likely that differences exist between European and Chinese breeds, and the characteristics of these differences are not well defined.
The immune response to infection is complex and affects other functions. The availability of nutrients is largely controlled by intestinal absorption from the diet and is important, because nutrients are involved with many physiological functions. Electrophysiological processes in intestinal enterocytes are involved with nutrient uptake from the lumen into the cytosol of the cell and then into circulation (Wright and Loo, 2000; Ray et al., 2002). For example, when glucose is actively transported from the lumen into the cytosol, it is coupled with Na in a fixed molar ratio (Wright and Loo, 2000). Therefore, by measuring changes in charge induced by the addition of specific nutrients, electrophysiological nutrient transport can be assessed. Lipopolysaccharide (LPS), a membrane component of gram-negative bacteria, is a common tool used to induce acute immune responses, and its effects on pigs have been well characterized (Johnson and von Borell, 1994).
This study sought to examine the effects of pig breed and LPS on intestinal nutrient transport.
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MATERIALS AND METHODS
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Animals
All procedures involving the pigs were approved by the Laboratory Animal Care Advisory Committee of the University of Illinois.
Gilts were obtained from the Imported Swine Research Laboratory, University of Illinois. The pigs were housed individually in temperature- and light-controlled rooms at the Edward R. Madigan Laboratory, University of Illinois. Yorkshire-based hybrid pigs (Yorkshire-Landrace, University of Illinois; n = 13; initial mean BW = 142.4 ± 2.0 kg; mean age = 8 mo) and purebred Meishan pigs (n = 10; initial mean BW = 65.8 ± 0.8 kg; mean age = 6 mo) were randomly assigned within breed to either control (6 Yorkshire, 5 Meishan) or LPS (7 Yorkshire, 5 Meishan) groups. The pigs were offered a commercial production diet [consisting of ground corn, soybean meal, fat, minerals, and vitamins; 13.5% CP (as-fed basis)] and water ad libitum.
Approximately 24 h before LPS infusion, all pigs underwent placement of an ear vein catheter for LPS or saline infusions and for euthanasia. Pigs were sedated with an i.m. mixture of telazol-ketamine-xylazine. Ketamine HCl and xylazine HCl (2.5 mL each; both 100 mg/mL) were added to a 500-mg vial of tiletamine HCl and zolazepam HCl (telazol, 100 mg/mL when reconstituted in 5 mL; Fort Dodge Animal Health, Fort Dodge, IA). After shaving the ear hair, a temporary tourniquet was used to induce swelling. Then, the surgical site was prepared aseptically with I and 70% alcohol. A 14-gauge, 3.8-cm sterile needle was inserted into the ear vein on the dorsal surface. After removal of the tourniquet, sterile tubing (1.3-mm o.d., 0.8-mm i.d., Allegiance Healthcare, McGaw, IL) was inserted through the needle about 45 cm into the jugular vein. The catheter was secured with hip tag cement (Nasco, Fort Atkinson, WI), and elastic tape (Elastikon, Johnson and Johnson, New Brunswick, NJ) was used to secure the catheter to the midpoint of the back. All pigs were then allowed to recover from surgery and were monitored during this time.
After a 12-h food deprivation, pigs were given a 5-mL i.v. infusion of sterile saline (0.9% NaCl; control) or LPS (5 µg/kg of BW; Johnson and von Borell, 1994). Lipopolysaccharide from Escherichia coli serotype K-235 (phenol-extracted; Sigma Chemical Company, St. Louis, MO) was dissolved in sterile saline (250 µg/mL). The solution was stored overnight at 4°C before injection and was mixed for 5 min before administration. Rectal temperatures were taken every 20 min. Four hours after LPS (Johnson and von Borell, 1994), pigs were euthanized by i.v. infusion of pentobarbital Na (390 mg/mL) and propylene glycol (0.01 mL/mL; Fatal Plus, Vortech Pharmaceuticals, Dearborn, MI). The dosage instructions on the bottle were followed for the euthanasia procedure. Samples of duodenum (immediately caudal to the stomach, approximately 5 cm), cranial jejunum (5 cm caudal to the ligament of Treitz), and caudal ileum (5 cm cranial to the ileocecal junction) were removed and placed in oxygenated Krebs’ solution (1.15 M NaCl, 260 mM NaHCO3, 120 mM MgCl2·6 H2O, 120 mM CaCl2, 40 mM KH2PO4, and 240 mM K2HPO4, pH = 7.4) on ice for transport and barrier function studies.
Electrophysiological Nutrient Transport
The procedures for measuring nutrient transport in modified Ussing chambers have been described previously (Kles and Tappenden, 2002). The 3 small intestinal tissue samples were carefully opened along the mesenteric border with scissors, and the mucosa was inspected for digestive particles and debris. If digesta was present, it was carefully flushed away using a syringe of Krebs’ solution (approximately 1 to 2 mL). However, due to the 12-h food deprivation, this was usually unnecessary. The serosal tissue was gently removed, and duplicate samples of tissue were mounted in modified Ussing chambers (Physiological Instruments, San Diego, CA) containing pairs of current and voltage electrodes housed in 3% agar bridges and filled with 3 M KCl. Krebs’ solution was added to mucosal and serosal chambers, which were continuously oxygenated (95% O2 + 5% CO2) and maintained at 37°C with a circulating water bath. After a short-circuit current was established and stabilized (about 5 to 10 min), basal short-circuit current measurements were taken using software (Acquire & Analyze, Physiological Instruments). The software allowed real-time measurements of current by displaying them as line graphs on a computer interface, and thus, changes in current were constantly monitored. All of the data points were automatically saved by the software to allow for further review at a later time.
After the basal measurements were taken, electrophysiological nutrient transport measurements were taken. One nutrient (for example, D-glucose) was added to the mucosal chamber to a final concentration of 10 mM, and the change in short-circuit current induced by its addition was recorded. After stabilization (usually less than 5 min), other nutrients were added individually to a final concentration of 10 mM each. Transport of D-glucose, L-Gln, glycylsarcosine (a synthetic dipeptide with a stable peptide bond), L-Pro, L-Arg, and L-Thr was examined in this order. Nutrients were chosen to examine most known nutrient transporters (Ray et al., 2002). Immediately after each nutrient was added to the mucosal chamber, 10 mM mannitol was added to the serosal chamber as an osmotic control. All tissues were treated equally to minimize variation and to allow for relative comparisons.
Intestinal Barrier Function
Barrier function was examined using the modified Ussing chambers by obtaining resistance measurements. An external pulse current was repeatedly applied to the mounted tissue to create a potential difference, which caused a change in short-circuit current that was measured with the software. Using Ohm’s law, resistance was calculated in each small intestinal segment. Resistance was calculated after short-circuit current had stabilized and before any nutrients were added to the mucosal chamber.
Statistical Analyses
All data were analyzed statistically using ANOVA and a software package (SAS Inst. Inc., Cary, NC), assuming each pig was an experimental unit. The experiment was a completely randomized design and was designed to assess the following: 1) the effect of LPS within pig breed and 2) the effect of pig breed within the control groups. Therefore, only these preplanned contrasts are reported. Normality was assessed using the univariate procedures of SAS. Means and SEM were generated using the MIXED procedure of SAS, and, when appropriate, multiple contrasts were made by examining protected P-values. Immune challenge status (saline and LPS infusions) and pig breed (Yorkshire and Meishan) and segment were main effects in the 2 x 2 factorial arrangement of treatments. If the interaction was not significantly different, only significant main effects were examined. Statistical significance was proclaimed when P < 0.05.
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RESULTS
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All pigs appeared to be in good health and acted normally before LPS infusion. Pigs that were given LPS exhibited increased rectal temperatures (39.6 ± 0.1 vs. 38.5 ± 0.1°C, mean rectal temperatures over the 4-h period, data not shown) during the 4-h period after infusion.
LPS and Electrophysiological Nutrient Transport
Small intestinal nutrient transport in Yorkshire and Meishan pigs responded differently to LPS infusion. Sodium-dependent glucose transport was not affected (P 
0.23) by LPS in the duodenum or jejunum of either breed (data not shown). In the ileum, Yorkshire pigs responded to LPS by decreasing (P < 0.001) glucose transport to less than 33% of control values, whereas Meishan pigs increased (P < 0.001) glucose transport by nearly 2.5-fold with LPS infusion (Figure 1). Control Meishans transported less (P = 0.009) glucose than control Yorkshires in the ileum (Figure 1). Gln transport was not affected (P 0.15) by LPS in the duodenum or jejunum of either pig breed (data not shown). Likewise, in the Meishan ileum, Gln transport was not affected (P = 0.39) by LPS (Figure 2). However, in Yorkshire ileum, LPS decreased (P = 0.002) Gln transport to about 40% of control values (Figure 2). In the absence of LPS, Yorkshire pigs transported more (P = 0.01) Gln than Meishan pigs (Figure 2). Jejunal Pro transport was unaffected (P 0.65) by LPS infusion in either breed. Meishan pigs exhibited increased (P 
0.04) Pro transport in duodenum (approximately 5-fold) and ileum (10-fold) when infused with LPS, whereas Pro transport was unaffected (P 0.50) by LPS in Yorkshire duodenum and ileum (Figures 3 and 4). Arginine transport was not affected (P 0.40) by LPS or breed in duodenum and jejunum. Arginine transport in the ileum was greater (P = 0.05) in control Meishans compared with control Yorkshires (Figure 5). Duodenal Thr transport was decreased (P = 0.05) by LPS to about 10% of control transport levels in Yorkshire pigs and was unaffected (P = 0.97) by LPS in Meishans (Figure 6). Control Yorkshire pigs transported more (P = 0.05) Thr than control Meishan pigs in the duodenum (Figure 6). Jejunal Thr transport was unaffected (P 0.71) by LPS in either breed. In the ileum, LPS did not affect (P = 0.14) Thr transport in either breed (Figure 7). However, control Meishans transported more (P < 0.001) Thr than control Yorkshire pigs in the ileum (Figure 7). Transport of glycylsarcosine, a synthetic dipeptide, was over 2-fold greater (P = 0.003) with LPS infusion compared with control, regardless of breed (pooled among the 3 intestinal segments; Figure 8). In addition, glycylsarcosine transport was nearly 2-fold greater (P = 0.02) in Meishans compared with Yorkshires, regardless of LPS treatment or intestinal segment (pooled among the 3 intestinal segments; Figure 9).
LPS and Intestinal Barrier Function
Small intestinal barrier function in Yorkshires and Meishans responded differently to LPS infusion. Yorkshire pigs responded to LPS by increasing (P = 0.03) resistance, regardless of small intestinal segment (pooled among the 3 intestinal segments; Figure 10). However, Meishan pigs did not exhibit any change (P 0.20) in small intestinal resistance after LPS infusion (Figure 10).
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DISCUSSION
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The current study indicates that small intestinal function in 2 pig breeds responded differently to LPS exposure. Interestingly, these responses depended on the nutrient examined and segment of the small intestine examined. For example, Na-dependent glucose transport was decreased in Yorkshires with LPS, whereas the opposite effect was observed in Meishans. These effects were only observed in the ileum. However, Yorkshires transported less Gln with LPS, whereas Meishans exhibited no change in Gln transport with LPS in the ileum. In general, Yorkshires exhibited decreased nutrient transport with LPS infusion, whereas Meishans responded to LPS by increasing nutrient transport. Studies comparing gastrointestinal physiology or function in different breeds of pigs are few. Chester White and Hampshire pigs exhibited different lactase activities during normal small intestinal development (Ekstrom et al., 1975). Female Meishan and Yorkshire pigs, aged somewhat older than the pigs used in this study, had similar small intestinal weights (White et al., 1995). Also, to the best of our knowledge, this is the first study to report increased small intestinal nutrient transport during acute LPS exposure in an ex vivo model. Rabbits given LPS exhibited decreased jejunal L-sLeu absorption (about 30%), and this was attributed to decreased Vmax (the nutrient concentration at which absorption becomes maximized) and Na+/K+ ATPase activity (Abad et al., 2001). When rats were given LPS, jejunal water and glucose absorption were decreased 90 min later (Cullen et al., 1999). Pigs given LPS absorbed less Na+, water, and glucose 2 h at the ileum after administration (Kanno et al., 1996). Six hours after intraperitoneal injection of LPS, rats experienced decreased absorption of Glu, Leu, aminoisobutyric acid, and Pro, which was affected by LPS (Gardiner et al., 1995a). In the current study, Pro transport in the duodenum and ileum was markedly increased (by 5- and 10-fold, respectively) by LPS in Meishans only. Arginine transport was reduced as early as 6 h after i.v. LPS injections in rats, and this effect returned to normal after recovery from septic conditions (Gardiner et al., 1995b). Absorption of a drug (salicylate) was impaired by LPS given to rats and mice, and this impairment was attributed to a delay in gastric emptying (Hurwitz et al., 1975).
Animals typically respond to a wide range of stressors by increasing intestinal permeability and conductance (and hence, decreasing resistance; Soderholm and Perdue, 2001). In terms of LPS treatment, challenged pigs responded by allowing more radiolabeled EDTA to permeate the ileum after 210 min of observation, and this was correlated with decreased mesenteric perfusion (Fink et al., 1991b). In addition, pigs treated with LPS exhibited increased intestinal permeability to markers, and either mesenteric hypoperfusion or other factors were attributed to this effect (Fink et al., 1991a). In the current study, Yorkshire pigs responded to LPS by increasing resistance (decreasing conductance), whereas resistance in Meishan intestine did not change with LPS. Interestingly, resistance was not affected by segment of small intestine in the current study. Resistance is generally believed to increase at more caudal segments of intestine, but different measurement methods have been shown to give somewhat different results (Nejdfors et al., 2000).
The underlying mechanisms responsible for the differences observed in the current study are unclear. Meishans have greater circulating concentrations of cortisol (Wise et al., 2001), and LPS infusion is known to increase circulating concentrations of cortisol within 2 h (Wright et al., 2000). Provision of synthetic glucocorticoids to rabbits resulted in increased glucose and Leu transport at 8 and 24 h and increased Gln, Ala, and Arg at 24 h (Iannoli et al., 1998). Although the mechanisms responsible for the breed differences reported in this study are unclear, the findings of this study highlight previously unknown breed differences in intestinal function during acute immune challenge. Further studies, designed to examine breed differences, should be conducted.
The results of the current study indicate that small intestinal function (nutrient uptake) of female Meishan pigs and female Yorkshire pigs typically used for commercial production responded in opposite ways to an immune challenge (LPS). Meishan pigs responded by increasing small intestinal function, whereas Yorkshire pigs responded by decreasing small intestinal function, after a 4-h exposure to LPS. Therefore, the genetic differences between the 2 pig breeds that are responsible for these effects should be determined, because small intestinal function is an important component of feed efficiency, growth performance, and nutrient excretion in manure. Further studies to determine the mechanisms of these differences are warranted and may lead to improved pig breeds for commercial production.
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Footnotes
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1 Financial support was provided by a Horizon Research Grant from Cargill Corporation to R. A. Nowak. 
2 Contributed equally to this work.
3 Present address: Agri-King, Research and Development, Fulton, IL 61252.
4 Corresponding author: ranowak{at}uiuc.edu
Received for publication April 13, 2006.
Accepted for publication May 16, 2007.
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Abstract
INTRODUCTION
µA/cm2) immediately after addition of nutrient to the Krebs’ solution surrounding the intestinal tissue mounted in modified Ussing chambers] as affected by pig breed and 4 h of lipopolysaccharide (LPS) exposure (interaction; P < 0.05). Error bars indicate SEM [n = 6 for Control Yorkshire (York); n = 7 for LPS Yorkshire; n = 5 for control and LPS Meishan groups]. The LPS Yorkshire group transported less (P < 0.001) glucose than the control Yorkshire group, whereas the LPS Meishan group transported more (P < 0.001) glucose than the control Meishan group. In addition, the control Yorkshire group transported more (P = 0.009) glucose than the control Meishan group. 
= breed effect without LPS.
x cm2); calculated using Ohm’s law and measured change in short-circuit current after creation of a potential difference in the modified Ussing chambers] as affected in Yorkshire (York) and Meishan pigs with or without 4 h of lipopolysaccharide (LPS) exposure (interaction; P < 0.05). Values are pooled among the 3 intestinal segments. Error bars indicate SEM (n = 18 for control Yorkshire; n = 21 for LPS Yorkshire; n = 15 for both control and LPS Meishan groups). Yorkshires treated with LPS exhibited increased (P = 0.03) transepithelial resistance.