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Zinc is involved in regulation of secretion from intestinal epithelium in weaned piglets
Livestock Science 108 (2007) 45 – 48 www.elsevier.com/locate/livsci
Zinc is involved in regulation of secretion from intestinal epithelium in weaned piglets ☆ D. Carlson a,⁎, J. Sehested a , Z. Feng b , H.D. Poulsen a a
Department of Animal Health, Welfare and Nutrition, Faculty of Agricultural Sciences, Research Centre Foulum, University of Aarhus, P.O. Box 50, 8830 Tjele, Denmark b Ministry of Agriculture Feed Industry Centre, Beijing, China
Abstract The objective was to study the effect of serosal zinc (Zn) on intestinal chloride (Cl−) secretion in vitro by the Ussing chamber technique. The secretagogues used to stimulate Cl− secretion were serotonin (5-HT), vasoactive intestinal polypeptide (VIP) and forskolin (FSK). In addition correlations between organ and plasma Zn levels vs. the responses to 5-HT were studied. The results revealed an attenuating effect of serosal Zn on the secretory response to 5-HT, VIP and FSK. Furthermore, negative correlations between secretory responses to 5-HT vs. ADG and plasma Zn concentrations were found, whereas the responses to 5-HT did not correlate to the Zn concentration in liver or intestinal mucosa. It is suggested, that dietary Zn reduces diarrhoea directly through a regulatory role of serosal Zn on Cl− secretion and indirectly by improving the nutritional status, which may stabilize the function of the intestinal epithelium. © 2007 Elsevier B.V. All rights reserved. Keywords: Ussing chamber; Serotonin (5-HT); Vasoactive intestinal polypeptide (VIP); Forskolin (FSK)
1. Introduction Dietary zinc (Zn) has a preventive impact on diarrhoea in newly weaned piglets (Poulsen, 1995), but the mechanisms behind are still not completely understood. When pathogenic bacteria secrete enterotoxins in the intestinal lumen the neurotransmitter 5-HT is
☆ This paper is part of the special issue entitled “Digestive Physiology in Pigs” guest edited by José Adalberto Fernández, Mette Skou Hedemann, Bent Borg Jensen, Henry Jørgensen, Knud Erik Bach Knudsen and Helle Nygaard Lærke. ⁎ Corresponding author. Tel.: +45 89 99 13 88; fax: +45 89 99 13 78. E-mail address: [email protected] (D. Carlson).
1871-1413/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2007.01.026
released from enterochromaffin cells located in the intestinal epithelium and a variety of receptors at the epithelial cells is activated resulting in chloride (Cl−) secretion (Skadhauge et al., 1997). Furthermore, 5-HT induces the release of other neurotransmitters (e.g. VIP) from enteric nerve endings which elevates intracellular messengers (e.g. cAMP) followed by Cl− secretion (Barrett and Keely, 2000). We have previously shown reduced epithelial responses to 5-HT in vitro when piglets were fed 2500 ppm of Zn compared to 100 ppm for 5 days after weaning (Carlson et al., 2004). Recently, we found a similar attenuating effect of Zn, on the response to 5-HT, VIP and carbachol, when 0.023 mM of Zn was added directly to the bathing media (Carlson et al., 2006). Similar in vitro studies with rat intestinal epithelium by Hoque et al. (2005) showed that 1 mM
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D. Carlson et al. / Livestock Science 108 (2007) 45–48
serosal Zn reduced Cl− secretion evoked by forskolin (FSK). This study aimed to elucidate the effect of serosal Zn on provoked ion secretion in vitro by use of the Ussing chamber technique. The secretagogues used to provoke Cl− secretion were serotonin (5-HT), vasoactive intestinal polypeptide (VIP) and forskolin (FSK). Furthermore, the correlation between the secretory capacity of the intestinal epithelium (measured as the 5-HT response in vitro) vs. the organ and plasma Zn concentrations of piglets was estimated. The presented data are obtained in two identical designed experiments. 2. Material and methods Both studies included 24 piglets that were weaned and allocated to two different diets at 28 days of age. The two diets were wheat-, barley- and soybean meal based diets supplied with either 100 or 2500 ppm of dietary Zn (from ZnO). At 5 or 6 days after weaning, individual blood samples were taken at 08:00 h and subsequently, the piglets were slaughtered at 09:00 or 13:00 h. The euthanasia procedure included stunning with a bolt gun and exsanguination. The piglets were weighed at the day of weaning and at the day of slaughter. Immediately after the piglets were killed, 30 cm of the middle of the small intestine was removed and placed in an oxygenated and phosphate-buffered Ringer solution at room temperature. For Zn measurements another 100 cm of small intestine (located proximal to the first site) was washed with cooled saline and the intestinal mucosa layer was scraped of. In addition, the liver from each piglet was collected. Plasma, mucosa and liver were analysed for Zn by atomic absorption spectrophotometry (Unicam SP9, Philips, Cambridge, UK). 2.1. Measurement of electrophysiological parameters Within 15 min after killing, the epithelium was stripped of the muscle layers and mounted in Ussing chambers (WPI, Sarasota, Fl, USA) in 3 and 4 replicates for exp 1 and 2, respectively. The conditions of the Ussing chamber experiments were analogous to the conditions described by Carlson et al. (2004). The bathing media (a Ringer solution) were replaced 10 min after mounting the tissue. Thereafter, the tissues equilibrated for 20 min, before 0.023 mM of ZnSO4 was added at the serosal side to 2 chambers (SZn) and a similar volume of water (200 μl, control) was added at the serosal side to 1 chamber (exp 1) or 2 chambers (exp 2). Twenty minutes
Fig. 1. The effect of Zn in the serosal bathing media (SZn) on changes in short circuit current (ΔIsc) induced by 0.1 mmol/l of 5-HT, 0.1 μmol/l Vasoactive Intestinal Polypeptide (VIP) and 10 μM forskolin (FSK) in piglet small intestinal epithelium. White bars represent a Zn free bathing media and black bars represent a serosal Zn concentration of 0.023 mmol/l. Values are least square means ± SEM, N = 47 piglets for 5-HT and N = 24 and 23 piglets for VIP and FSK, respectively, n = number of epithelial tissues per treatment. ⁎⁎ and ⁎⁎⁎ indicate that SZn differs significantly from the control (⁎⁎p ≤ .01 and ⁎⁎⁎p ≤ .001).
subsequently, 0.1 mM of 5-HT (Sigma, Copenhagen, Denmark) was added at the serosal side to all chambers followed 20 min later by 0.1 μM of VIP (Calbiochem, Albertslund, Denmark) (exp 1) or 10 μM FSK (Sigma, Copenhagen, Denmark) (exp 2) at the serosal side. The response (ΔIsc, change in short circuit current) to 5-HT, VIP and FSK was calculated by subtracting the basal Isc before addition from the peak Isc after addition of the secretagogue. 2.2. Statistical analysis Statistical analysis was carried out by the MIXED procedure in SAS (Littel et al., 1996) with the fixed effects of dietary Zn treatment (100, 2500 ppm), in vitro Zn treatment (control, SZn) and the interaction between them. Litter and interactions between litter and pig were included in the model as random effects. Results are presented as least square means ± SEM with N = number of piglets and n = number of epithelial tissues. Effects were considered significant at p ≤ 0.05. The pair-wise comparison procedure in SAS was used to separate the least square means. The CORR procedure in SAS was used to test correlations between the secretory responses to 5-HT versus the average daily gain (ADG), plasma, mucosa and liver Zn concentrations, respectively. Least square means for ADG, plasma Zn, mucosa Zn and liver Zn
D. Carlson et al. / Livestock Science 108 (2007) 45–48 Table 1 Correlation coefficients between the secretory response to 5-HT vs. the average daily gain (ADG), plasma Zn concentrations, liver Zn concentration and mucosa Zn concentrations, N = 47 piglets
ADG vs. 5-HT Plasma Zn vs. 5-HT Liver Zn vs. 5-HT Mucosa Zn vs. 5-HT
Correlation coefficients
p-value
− 0.46 − 0.26 − 0.04 0.09
≤0.0001 0.03 0.7 0.5
concentrations in exp 2 are presented elsewhere (Feng et al., 2006). 3. Results Least square means for the in vitro treatments are presented in Fig. 1, which show an attenuating effect of adding Zn at the serosal side on the secretory response to 5-HT, VIP and FSK. There was no effect of diet or interactions between diet and in vitro treatments ( p N 0.05) on the secretory responses to 5-HT, VIP or FSK. The only secretagogue that was added in both experiments was 5-HT and the statistical analysis revealed that there were no systematic differences between the two experiments with respect to the in vitro responses to 5-HT (data not shown). There were negative correlations between the 5-HT response vs. ADG ( p ≤ 0.0001) and vs. plasma Zn concentrations ( p = 0.03), whereas there were no correlations between the secretory responses to 5-HT vs. the Zn concentration in liver ( p = 0.7) or vs. the Zn concentration in mucosa ( p = 0.5) (Table 1). 4. Discussion This study showed that there were decreasing effects of Zn in the serosal bathing media on the secretagogue stimulated secretion from piglet intestinal epithelium in vitro. VIP and FSK act by increasing intracellular cAMP levels. In another study we found that Zn in vitro also reduced the responses to carbachol (Carlson et al., 2006). Carbachol activates secretion by increasing intracellular Ca2+ concentration. In neuronal studies, a blocking effect of Zn on Ca2+ channels was found (Magistretti et al., 2003). Hoque et al. (2005) found that Zn blocked the cAMP-activated K-channels at the basolateral membrane of the epithelial cells. Consequently, the attenuating effect of Zn on Cl− secretion may be due to Zn blocking cation channels at the basolateral membrane, and hence reducing the electrochemical driving force for Cl− secretion. The small reduction in secretion when adding 0.023 mM Zn in the
47
present study compared with the complete blocking effect of 1 mM Zn in the study of Hoque et al. (2005) indicates that Zn concentrations at normal plasma levels (0.023 mM) could represent a physiological mechanism of Zn in regulation of Cl− secretion from epithelial cells. The lacking effect of dietary Zn on the 5-HT response is in contrast to previous data (Carlson et al., 2004). In the present study plasma Zn increased with dietary Zn, whereas ADG was not significantly affected (Feng et al., 2006). However, in our previous study there was a significant and more pronounced effect of dietary Zn on ADG and plasma Zn concentrations. Hence, considering the correlations in the present study, it may be speculated that the effect of dietary Zn on the 5-HT response in our previous study was an indirect effect of increased nutritional status (increased ADG and plasma Zn) on the morphology of the mucosal tissue rather than an effect of increased mucosal Zn concentration per se. Increased villus height to crypt depth ratios of small intestinal epithelium were found in piglets fed high Zn concentrations post weaning (Li et al., 2001). Consequently, as the secretory cells are situated in the crypts, the reduced secretion in epithelium from piglets fed high dietary Zn concentrations may be due to relatively less secretory cells rather than an effect of increased intracellular mucosal Zn concentrations. 5. Conclusion The presented data suggest that high concentrations of dietary Zn post weaning reduce the intestinal sensitivity to diarrhoea inducing challenges directly through a regulatory role of serosal Zn on Cl− secretion and indirectly by improving the nutritional status, which may stabilize the epithelial function. References Barrett, K.E., Keely, S.J., 2000. Chloride secretion by the intestinal epithelium: molecular basis and regulatory aspects. Annu. Rev. Physiol. 62, 535–572. Carlson, D., Poulsen, H.D., Sehested, J., 2004. Influence of weaning and effect of post weaning dietary zinc and copper on electrophysiological response to glucose, theophylline and 5-HT in piglet small intestinal mucosa. Comp. Biochem. Physiol. A 137, 757–765. Carlson, D., Sehested, J., Poulsen, H.D., 2006. Zinc reduces the electrophysiological responses in vitro to basolateral receptor mediated secretagogues in piglet small intestinal epithelium. Comp. Biochem. Physiol. 144, 514–519. Feng, Z., Carlson, D., Poulsen, H.D., 2006. Zinc attenuates forskolinstimulated electrolyte secretion without involvement of the enteric nervous system in small intestinal epithelium from weaned piglets. Comp. Biochem. Physiol. A 145, 328–333.
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D. Carlson et al. / Livestock Science 108 (2007) 45–48
Hoque, K.M., Rajendran, V.M., Binder, H.J., 2005. Zinc inhibits cAMP-stimulated Cl secretion via basolateral K-channel blockade in rat ileum. Am. J. Physiol.: Gasterointest. Liver Physiol. 288, G956–G963. Li, B.T., Van Kessel, A.G., Caine, W.R., Huang, S.X., Kirkwood, R.N., 2001. Small intestinal morphology and bacterial populations in ileal digesta and feces of newly weaned pigs receiving a high dietary level of zinc oxide. Can. J. Anim. Sci. 81, 511–516. Littel, R.C., Milliken, G.A., Stroup, W.W., Wolfinger, R.D., 1996. SAS Systems for Mixed Models. SAS Institute Inc, North Carolina, USA.
Magistretti, J., Castelli, L., Taglietti, V., Tanzi, F., 2003. Dual effect of Zn2+ on multiple types of voltage-dependent Ca2+ currents in rat palaeocortical neurons. Neuroscience 117, 249–264. Poulsen, H.D., 1995. Zinc oxide for weanling piglets. Acta Agric. Scand. 45, 159–167. Skadhauge, E., Grøndahl, M.L., Hansen, M.B., 1997. Pathophysiology and symptomatic treatment of secretory and osmotic diarrhoea. In: Laplace, J.P., Février, C., Barbeau, A. (Eds.), EAAP publications, Saint Malo, France, pp. 241–254.
Zinc is involved in regulation of secretion from intestinal epithelium in weaned piglets ☆ D. Carlson a,⁎, J. Sehested a , Z. Feng b , H.D. Poulsen a a
Department of Animal Health, Welfare and Nutrition, Faculty of Agricultural Sciences, Research Centre Foulum, University of Aarhus, P.O. Box 50, 8830 Tjele, Denmark b Ministry of Agriculture Feed Industry Centre, Beijing, China
Abstract The objective was to study the effect of serosal zinc (Zn) on intestinal chloride (Cl−) secretion in vitro by the Ussing chamber technique. The secretagogues used to stimulate Cl− secretion were serotonin (5-HT), vasoactive intestinal polypeptide (VIP) and forskolin (FSK). In addition correlations between organ and plasma Zn levels vs. the responses to 5-HT were studied. The results revealed an attenuating effect of serosal Zn on the secretory response to 5-HT, VIP and FSK. Furthermore, negative correlations between secretory responses to 5-HT vs. ADG and plasma Zn concentrations were found, whereas the responses to 5-HT did not correlate to the Zn concentration in liver or intestinal mucosa. It is suggested, that dietary Zn reduces diarrhoea directly through a regulatory role of serosal Zn on Cl− secretion and indirectly by improving the nutritional status, which may stabilize the function of the intestinal epithelium. © 2007 Elsevier B.V. All rights reserved. Keywords: Ussing chamber; Serotonin (5-HT); Vasoactive intestinal polypeptide (VIP); Forskolin (FSK)
1. Introduction Dietary zinc (Zn) has a preventive impact on diarrhoea in newly weaned piglets (Poulsen, 1995), but the mechanisms behind are still not completely understood. When pathogenic bacteria secrete enterotoxins in the intestinal lumen the neurotransmitter 5-HT is
☆ This paper is part of the special issue entitled “Digestive Physiology in Pigs” guest edited by José Adalberto Fernández, Mette Skou Hedemann, Bent Borg Jensen, Henry Jørgensen, Knud Erik Bach Knudsen and Helle Nygaard Lærke. ⁎ Corresponding author. Tel.: +45 89 99 13 88; fax: +45 89 99 13 78. E-mail address: [email protected] (D. Carlson).
1871-1413/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2007.01.026
released from enterochromaffin cells located in the intestinal epithelium and a variety of receptors at the epithelial cells is activated resulting in chloride (Cl−) secretion (Skadhauge et al., 1997). Furthermore, 5-HT induces the release of other neurotransmitters (e.g. VIP) from enteric nerve endings which elevates intracellular messengers (e.g. cAMP) followed by Cl− secretion (Barrett and Keely, 2000). We have previously shown reduced epithelial responses to 5-HT in vitro when piglets were fed 2500 ppm of Zn compared to 100 ppm for 5 days after weaning (Carlson et al., 2004). Recently, we found a similar attenuating effect of Zn, on the response to 5-HT, VIP and carbachol, when 0.023 mM of Zn was added directly to the bathing media (Carlson et al., 2006). Similar in vitro studies with rat intestinal epithelium by Hoque et al. (2005) showed that 1 mM
46
D. Carlson et al. / Livestock Science 108 (2007) 45–48
serosal Zn reduced Cl− secretion evoked by forskolin (FSK). This study aimed to elucidate the effect of serosal Zn on provoked ion secretion in vitro by use of the Ussing chamber technique. The secretagogues used to provoke Cl− secretion were serotonin (5-HT), vasoactive intestinal polypeptide (VIP) and forskolin (FSK). Furthermore, the correlation between the secretory capacity of the intestinal epithelium (measured as the 5-HT response in vitro) vs. the organ and plasma Zn concentrations of piglets was estimated. The presented data are obtained in two identical designed experiments. 2. Material and methods Both studies included 24 piglets that were weaned and allocated to two different diets at 28 days of age. The two diets were wheat-, barley- and soybean meal based diets supplied with either 100 or 2500 ppm of dietary Zn (from ZnO). At 5 or 6 days after weaning, individual blood samples were taken at 08:00 h and subsequently, the piglets were slaughtered at 09:00 or 13:00 h. The euthanasia procedure included stunning with a bolt gun and exsanguination. The piglets were weighed at the day of weaning and at the day of slaughter. Immediately after the piglets were killed, 30 cm of the middle of the small intestine was removed and placed in an oxygenated and phosphate-buffered Ringer solution at room temperature. For Zn measurements another 100 cm of small intestine (located proximal to the first site) was washed with cooled saline and the intestinal mucosa layer was scraped of. In addition, the liver from each piglet was collected. Plasma, mucosa and liver were analysed for Zn by atomic absorption spectrophotometry (Unicam SP9, Philips, Cambridge, UK). 2.1. Measurement of electrophysiological parameters Within 15 min after killing, the epithelium was stripped of the muscle layers and mounted in Ussing chambers (WPI, Sarasota, Fl, USA) in 3 and 4 replicates for exp 1 and 2, respectively. The conditions of the Ussing chamber experiments were analogous to the conditions described by Carlson et al. (2004). The bathing media (a Ringer solution) were replaced 10 min after mounting the tissue. Thereafter, the tissues equilibrated for 20 min, before 0.023 mM of ZnSO4 was added at the serosal side to 2 chambers (SZn) and a similar volume of water (200 μl, control) was added at the serosal side to 1 chamber (exp 1) or 2 chambers (exp 2). Twenty minutes
Fig. 1. The effect of Zn in the serosal bathing media (SZn) on changes in short circuit current (ΔIsc) induced by 0.1 mmol/l of 5-HT, 0.1 μmol/l Vasoactive Intestinal Polypeptide (VIP) and 10 μM forskolin (FSK) in piglet small intestinal epithelium. White bars represent a Zn free bathing media and black bars represent a serosal Zn concentration of 0.023 mmol/l. Values are least square means ± SEM, N = 47 piglets for 5-HT and N = 24 and 23 piglets for VIP and FSK, respectively, n = number of epithelial tissues per treatment. ⁎⁎ and ⁎⁎⁎ indicate that SZn differs significantly from the control (⁎⁎p ≤ .01 and ⁎⁎⁎p ≤ .001).
subsequently, 0.1 mM of 5-HT (Sigma, Copenhagen, Denmark) was added at the serosal side to all chambers followed 20 min later by 0.1 μM of VIP (Calbiochem, Albertslund, Denmark) (exp 1) or 10 μM FSK (Sigma, Copenhagen, Denmark) (exp 2) at the serosal side. The response (ΔIsc, change in short circuit current) to 5-HT, VIP and FSK was calculated by subtracting the basal Isc before addition from the peak Isc after addition of the secretagogue. 2.2. Statistical analysis Statistical analysis was carried out by the MIXED procedure in SAS (Littel et al., 1996) with the fixed effects of dietary Zn treatment (100, 2500 ppm), in vitro Zn treatment (control, SZn) and the interaction between them. Litter and interactions between litter and pig were included in the model as random effects. Results are presented as least square means ± SEM with N = number of piglets and n = number of epithelial tissues. Effects were considered significant at p ≤ 0.05. The pair-wise comparison procedure in SAS was used to separate the least square means. The CORR procedure in SAS was used to test correlations between the secretory responses to 5-HT versus the average daily gain (ADG), plasma, mucosa and liver Zn concentrations, respectively. Least square means for ADG, plasma Zn, mucosa Zn and liver Zn
D. Carlson et al. / Livestock Science 108 (2007) 45–48 Table 1 Correlation coefficients between the secretory response to 5-HT vs. the average daily gain (ADG), plasma Zn concentrations, liver Zn concentration and mucosa Zn concentrations, N = 47 piglets
ADG vs. 5-HT Plasma Zn vs. 5-HT Liver Zn vs. 5-HT Mucosa Zn vs. 5-HT
Correlation coefficients
p-value
− 0.46 − 0.26 − 0.04 0.09
≤0.0001 0.03 0.7 0.5
concentrations in exp 2 are presented elsewhere (Feng et al., 2006). 3. Results Least square means for the in vitro treatments are presented in Fig. 1, which show an attenuating effect of adding Zn at the serosal side on the secretory response to 5-HT, VIP and FSK. There was no effect of diet or interactions between diet and in vitro treatments ( p N 0.05) on the secretory responses to 5-HT, VIP or FSK. The only secretagogue that was added in both experiments was 5-HT and the statistical analysis revealed that there were no systematic differences between the two experiments with respect to the in vitro responses to 5-HT (data not shown). There were negative correlations between the 5-HT response vs. ADG ( p ≤ 0.0001) and vs. plasma Zn concentrations ( p = 0.03), whereas there were no correlations between the secretory responses to 5-HT vs. the Zn concentration in liver ( p = 0.7) or vs. the Zn concentration in mucosa ( p = 0.5) (Table 1). 4. Discussion This study showed that there were decreasing effects of Zn in the serosal bathing media on the secretagogue stimulated secretion from piglet intestinal epithelium in vitro. VIP and FSK act by increasing intracellular cAMP levels. In another study we found that Zn in vitro also reduced the responses to carbachol (Carlson et al., 2006). Carbachol activates secretion by increasing intracellular Ca2+ concentration. In neuronal studies, a blocking effect of Zn on Ca2+ channels was found (Magistretti et al., 2003). Hoque et al. (2005) found that Zn blocked the cAMP-activated K-channels at the basolateral membrane of the epithelial cells. Consequently, the attenuating effect of Zn on Cl− secretion may be due to Zn blocking cation channels at the basolateral membrane, and hence reducing the electrochemical driving force for Cl− secretion. The small reduction in secretion when adding 0.023 mM Zn in the
47
present study compared with the complete blocking effect of 1 mM Zn in the study of Hoque et al. (2005) indicates that Zn concentrations at normal plasma levels (0.023 mM) could represent a physiological mechanism of Zn in regulation of Cl− secretion from epithelial cells. The lacking effect of dietary Zn on the 5-HT response is in contrast to previous data (Carlson et al., 2004). In the present study plasma Zn increased with dietary Zn, whereas ADG was not significantly affected (Feng et al., 2006). However, in our previous study there was a significant and more pronounced effect of dietary Zn on ADG and plasma Zn concentrations. Hence, considering the correlations in the present study, it may be speculated that the effect of dietary Zn on the 5-HT response in our previous study was an indirect effect of increased nutritional status (increased ADG and plasma Zn) on the morphology of the mucosal tissue rather than an effect of increased mucosal Zn concentration per se. Increased villus height to crypt depth ratios of small intestinal epithelium were found in piglets fed high Zn concentrations post weaning (Li et al., 2001). Consequently, as the secretory cells are situated in the crypts, the reduced secretion in epithelium from piglets fed high dietary Zn concentrations may be due to relatively less secretory cells rather than an effect of increased intracellular mucosal Zn concentrations. 5. Conclusion The presented data suggest that high concentrations of dietary Zn post weaning reduce the intestinal sensitivity to diarrhoea inducing challenges directly through a regulatory role of serosal Zn on Cl− secretion and indirectly by improving the nutritional status, which may stabilize the epithelial function. References Barrett, K.E., Keely, S.J., 2000. Chloride secretion by the intestinal epithelium: molecular basis and regulatory aspects. Annu. Rev. Physiol. 62, 535–572. Carlson, D., Poulsen, H.D., Sehested, J., 2004. Influence of weaning and effect of post weaning dietary zinc and copper on electrophysiological response to glucose, theophylline and 5-HT in piglet small intestinal mucosa. Comp. Biochem. Physiol. A 137, 757–765. Carlson, D., Sehested, J., Poulsen, H.D., 2006. Zinc reduces the electrophysiological responses in vitro to basolateral receptor mediated secretagogues in piglet small intestinal epithelium. Comp. Biochem. Physiol. 144, 514–519. Feng, Z., Carlson, D., Poulsen, H.D., 2006. Zinc attenuates forskolinstimulated electrolyte secretion without involvement of the enteric nervous system in small intestinal epithelium from weaned piglets. Comp. Biochem. Physiol. A 145, 328–333.
48
D. Carlson et al. / Livestock Science 108 (2007) 45–48
Hoque, K.M., Rajendran, V.M., Binder, H.J., 2005. Zinc inhibits cAMP-stimulated Cl secretion via basolateral K-channel blockade in rat ileum. Am. J. Physiol.: Gasterointest. Liver Physiol. 288, G956–G963. Li, B.T., Van Kessel, A.G., Caine, W.R., Huang, S.X., Kirkwood, R.N., 2001. Small intestinal morphology and bacterial populations in ileal digesta and feces of newly weaned pigs receiving a high dietary level of zinc oxide. Can. J. Anim. Sci. 81, 511–516. Littel, R.C., Milliken, G.A., Stroup, W.W., Wolfinger, R.D., 1996. SAS Systems for Mixed Models. SAS Institute Inc, North Carolina, USA.
Magistretti, J., Castelli, L., Taglietti, V., Tanzi, F., 2003. Dual effect of Zn2+ on multiple types of voltage-dependent Ca2+ currents in rat palaeocortical neurons. Neuroscience 117, 249–264. Poulsen, H.D., 1995. Zinc oxide for weanling piglets. Acta Agric. Scand. 45, 159–167. Skadhauge, E., Grøndahl, M.L., Hansen, M.B., 1997. Pathophysiology and symptomatic treatment of secretory and osmotic diarrhoea. In: Laplace, J.P., Février, C., Barbeau, A. (Eds.), EAAP publications, Saint Malo, France, pp. 241–254.