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ANIMAL NUTRITION |
Department of Animal Sciences, University of Kentucky, Lexington 40546-0215
Abstract
Eight Angus steers (290 ± 8 kg), surgically prepared with pancreatic pouch-duodenal reentrant cannulas and abomasal infusion catheters were used in a replicated 4 x 4 Latin square experiment to investigate the effects of abomasal infusion of starch hydrolyzate (SH) and/or casein on pancreatic exocrine secretion and plasma concentration of hormones. Steers were fed a basal diet of alfalfa (1.2 x NEm) in 12 equal portions daily. Abomasal infusion treatments (6-L total volume infused per day) were water (control), SH [2.7 g/(kg BW•d)], casein [0.6 g/(kg BW•d)], and SH + casein. Periods were 3 d for adaptation and 8 d of full infusion. Pancreatic juice and jugular blood samples were collected over 30-min intervals for 6 h on d 11. Weight and pH of pancreatic samples were measured, and a 10% subsample was composited and frozen until analysis of total protein and pancreatic enzyme activities. The remaining sample was returned to the duodenum. Plasma was harvested and frozen until analyzed. Pancreatic juice (67 mL/h) and protein (1.8 g/h) secretion rates were not affected by nutrient infusion. There were SH x casein interactions for all pancreatic enzyme secretions (U/h; 
-amylase, P < 0.03; trypsin, P < 0.08; and chymotrypsin, P < 0.03) and plasma insulin concentration (P < 0.10). Secretion of pancreatic enzymes was increased by SH (trypsin) and casein (-amylase, trypsin, and chymotrypsin) but not when SH + casein were infused together. Glucose (P < 0.10) and cholecystokinin octapeptide concentrations (CCK-8; P < 0.05) were increased by SH, but glucagon was decreased (P < 0.10). Casein decreased (P < 0.10) plasma CCK-8 concentrations. These data indicate that positive effects of postruminal casein on enzyme secretion were inhibited by SH, emphasizing the complexity of the regulatory mechanisms involved in dietary adaptation of pancreatic exocrine secretion. Changes in hormone concentration may not relate directly to changes in enzyme secretion.
Key Words: -Amylase • Hormones • Pancreatic Secretion • Protein • Ruminants • Starch
Introduction
Beef production in the United States utilizes large quantities of cereal grains. Although the majority of starch contained in grains is fermented in the rumen, significant amounts may reach the small intestine in cattle fed high-concentrate diets (Theurer, 1986
). It has been estimated that starch digestion in the small intestine is 42% more energetically efficient than ruminal fermentation (Owens et al., 1986). Therefore, the potential to improve the energetic efficiency of starch utilization for beef production exists. However, concomitant increases in large intestinal starch fermentation suggest that there are limits to small intestinal starch digestion in ruminants (Kreikemeier et al., 1991). Research has shown that abomasal infusion of partially hydrolyzed starch (SH) or glucose results in decreases in secretion of -amylase activity in steers (Walker and Harmon, 1995; Swanson et al., 2002b). Decreased secretion in response to increased substrate is not typical of the response of nonruminants (Brannon, 1990). However, increasing the postruminal supply of protein may have beneficial effects on -amylase secretion and starch digestion (Richards et al., 2003). It is not known how the presence of both starch and protein together at the small intestine might interact to affect -amylase secretion and starch digestion. The pancreatic response of ruminants is difficult to predict, and literature suggests complex interactions exist with nutrients and hormones in ruminants (Swanson and Harmon, 2002). It was hypothesized that increasing postruminal protein may be a way to increase -amylase secretion and improve postruminal starch digestion in beef steers. Therefore, the objectives of the following experiment were to evaluate how increased small intestinal carbohydrate and protein interact to influence pancreatic enzyme secretion and plasma concentrations of some gastrointestinal hormones.
Materials and Methods
Animals and Diet.
Surgical procedures, postsurgical care, and the experimental protocol were approved by the University of Kentucky Institutional Animal Care and Use Committee. Eight Angus steers (mean initial body weight 290 ± 8 kg) were used in the experiment. Under general anesthesia, animals were surgically prepared with a pancreatic pouch into which the main pancreatic duct drains (St. Jean et al., 1992), and fitted with cannulas in the pancreatic pouch and duodenum for quantitative collection of pancreatic juice as described by Swanson et al. (2002b). Catheters for infusion were made and placed in the abomasum as described previously (Richards et al., 2003). Animals were housed individually in 3- x 3.2-m pens with concrete floors in a temperature- and light-controlled (respectively, 23°C and 16 h of light/8 h of dark) room with water available at all times. Steers were weighed before each treatment period. The basal forage diet (Table 1), chosen to minimize dietary starch flow to the small intestine (Branco et al., 1999), was fed at 17.5 g/kg of BW. This was supplemented with a mineral mix at 0.15 g/kg of BW. The diet was formulated to supply 1.2 x NEm requirements of a steer gaining 0.2 kg/d (NRC, 1996), and intakes were adjusted each period. Daily feed allowances were divided into 12 equal portions and fed every 2 h using automatic feeders (SS100; Ankom, Fairport, NY).
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-amylase (Takatherm L-340; Solvay Enzymes, Elkhart, IN) and was used because its digestion characteristics are similar to native starch passing through the small intestine (Bauer et al., 1995; Walker and Harmon, 1995). The amounts of SH infused were similar to starch flow in the small intestine when moderate- to high-starch diets are fed to beef cattle (Theurer, 1986). In previous experiments, similar amounts of SH have elicited negative effects on -amylase secretion (Swanson et al., 2002b) and similar amounts of casein have elicited positive effects on -amylase secretion (Richards et al., 2003). Abomasal infusion periods were 11 d, the first 3 d being a period of adaptation in which 25, 50, and 75% of the total amount calculated for each animal were infused. A rest period of at least 10 d separated the infusion periods.
Sample Collection.
Samples of pancreatic juice and jugular blood were collected from the steers at 30-min intervals for a period of 6 h on the last day of the abomasal infusion. Steers were fitted with jugular catheters (Abbocath-T, 14 gauge catheter; Abbott Laboratories, Abbott Park, IL) the day before sampling for blood collection. Pancreatic juice was collected under continuous vacuum (Walker et al., 1994) into ice-cooled flasks. At the start of the sampling period, the reentrant cannula was interrupted and rinsed out with water. Pancreatic juice was collected for 1 h, after which it was returned to the duodenum. This was necessary to eliminate any contamination of the pancreatic juice with feed particles. Thereafter, the weight and pH of each 30 min sample was recorded and a 10% subsample was composited and frozen at –30°C until analysis. The remaining sample was returned to the duodenum. Jugular blood samples (10 mL) were collected into heparinized syringes and immediately centrifuged to obtain plasma. Aliquots of plasma were placed in separate tubes for each analysis to be performed and frozen (–80°C) until analyzed. To limit breakdown of the hormones during storage, aprotinin (0.5 IU/mL; Fisher Scientific, Pittsburgh, PA) was added to the plasma.
Laboratory Analyses.
All analyses of pooled pancreatic juice samples were carried out within a week of their collection. Samples were analyzed for total protein and concentration of -amylase, trypsin, and chymotrypsin activities. Protein concentration was measured using the method of Lowry et al. (1951). Trypsin and chymotrypsin activities were measured colorimetrically using N-benzoyl-DL-arginine-4-nitroanilide (Geiger and Fritz, 1986) and N-succinyl-L-phenylalanine-p-nitroanilide (Wirnt, 1986) as substrates, respectively. These assays were adapted for use on a Cobas Fara II (Roche Diagnostics F; Hoffmann-La Roche, Basel, Switzerland). Concentration of -amylase activity in pancreatic juice was measured according to the method of Walker and Harmon (1996), which uses potato amylopectin as substrate. One unit of enzyme activity was defined as 1 µmol of product released per minute at 39°C.
Plasma samples were analyzed for glucose concentration using the hexokinase method (Slein, 1963; Sigma Chemical, St Louis, MO). Plasma concentrations of insulin, pancreatic glucagon and cholecystokinin octapeptide (CCK-8) were measured as described in Benson and Reynolds (2001). Pancreatic polypeptide (PP) concentration was measured using a commercial kit (American Laboratory Products Co., Windham, NH) validated for bovine plasma. The plasma concentration of insulin and glucagon was measured in individual samples. Plasma samples were pooled by steer and treatment within period for PP and CCK-8 analyses.
Statistical Analyses.
Mean values for each animal for each abomasal infusion period were calculated for each variable and subsequently used in the statistical analysis. Data were analyzed as a replicated 4 x 4 Latin square with a 2 x 2 factorial arrangement of treatments using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC). The statistical model included effects of square, period within square, animal within square, SH, casein, and the SH x casein interaction. Differences were considered significant when P < 0.10.
Results
Feed intakes were restricted to ensure rapid and complete consumption of meals yet to maintain a modest rate of growth and a positive energy balance. Feed intakes were complete and were unaffected by infusion treatment. Although we did not measure digestibility, there was no effect of infusion treatment on fecal quality indicative of poor intestinal digestion of infused nutrients.
There were no effects of SH, casein, or their interaction on the rate of secretion (67.0 g/h) or pH (8.31) of pancreatic juice (Table 2). Protein concentration of pancreatic juice (28.6 mg/mL) and rate of protein secretion (1.75 g/h) were also unaffected by the infusions or their interaction (Table 2).
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-amylase activity (units per milliliter) was decreased (P = 0.02) by SH infusion and increased (P = 0.03) by casein infusion. There was a trend (P = 0.11) for decreased -amylase-specific activity with SH infusion and -amylase-specific activity was increased (P = 0.09) by casein infusion (Table 2
). There was a SH x casein interaction (P = 0.03) for -amylase secretion (units per hour). Casein infusion increased -amylase secretion when infused alone, but not when infused with SH. Concentration of trypsin activity (units per liter) was unaffected by abomasal infusions; however, there was a SH x casein interaction (P < 0.10) for both specific activity and secretion of trypsin activity. Trypsin-specific activity was increased in response to SH infusion alone but not when SH + casein were infused together. Trypsin secretion was increased by SH and casein when they were infused individually, but not when they were infused in combination. Chymotrypsin concentration, specific activity, and secretion all exhibited SH x casein interactions (P < 0.05). Chymotrypsin concentration increased with SH but not with SH + casein. Infusion of SH and casein each increased chymotrypsin-specific activity and secretion compared with control or SH + casein treatments.
Plasma insulin concentration (picomoles per liter) exhibited a SH x casein interaction (P < 0.10). Insulin concentration was increased by infusions of SH and casein alone, but no additional increase was observed when SH + casein were infused together (Table 3). Abomasal SH infusion resulted in decreased plasma glucagon concentrations (P < 0.09), whereas casein did not influence glucagon. Plasma PP concentrations were not affected (74.5 pmol/L) by SH, casein, or their interaction. Plasma CCK-8 concentration was increased (P < 0.02) by abomasal SH infusion and decreased by casein infusion (P < 0.07; Table 3). Plasma glucose concentration was increased (P < 0.07) by SH infusion.
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Previous work has shown that postruminal starch infusion has a negative effect on secretion of -amylase activity in beef steers and this may be a major factor limiting the efficiency of digestion in the small intestine (Walker and Harmon, 1995). Postruminal casein infusion has been shown to increase -amylase secretion (Richards et al., 2003), and it was hypothesized that infusing casein with SH may have a positive effect on -amylase secretion and therefore improve starch digestion postruminally. In addition, regulatory signals coordinating these events are poorly understood. Gastrointestinal hormones are likely candidates but information describing their role is lacking.
Pancreatic Secretion
The results of the present study differed from those reported previously (Walker and Harmon, 1995; Swanson et al., 2002a,b; Swanson and Harmon, 2002) in that SH infusion did not decrease -amylase secretion. There was no negative effect of carbohydrate infusion on -amylase secretion; however, there was a decrease in -amylase concentration but this was overcome by a numerical increase in pancreatic juice secretion such that total -amylase secretion was unchanged. The decrease in -amylase concentration is consistent with our previous research (Walker and Harmon, 1995; Swanson et al., 2002b) as was an increase in secretion of pancreatic juice (numerical in the present study) with SH infusion (Walker and Harmon, 1995; Swanson et al., 2002b). The reason for the numerical increase in total secretion is unclear. Increases in pancreatic juice flow with abomasal SH infusion have been noted. Walker and Harmon (1995) observed that 34.4 g/h abomasal starch infusion increased pancreatic secretion from 117 g/d to 135 g/h in beef steers, and Swanson et al. (2002b) found that abomasal infusion of 20 to 40 g/h of SH or glucose resulted in linear increases in secretion of pancreatic juice in beef steers. This increase has been suggested to be a result of a possible decrease in intestinal pH due to intestinal fermentation of infused carbohydrate (Walker and Harmon, 1995). The gastrointestinal tract is the site of numerous luminal receptors, which receive signals from luminal materials to respond to digestive events, such as gastric distension and duodenal volume and osmolality (Dooley and Valenzuela, 1984). These luminal signals have been shown to contribute up to 50% of postprandial pancreatic secretion in rats (Li et al., 2000). In this experiment, the osmolality of the solutions differed, with solutions containing partially digested SH (SH and SH + casein) expected to be of greater osmolality than casein and water infusions. Whether infusion of these solutions directly into the abomasum influences the pancreatic secretory response is not known. In adult ruminants, the abomasum, which most nearly resembles the monogastric stomach, is generally thought to propel digesta into the duodenum because digesta outflow is more constant and less dependent on meals than in nonruminants (Merchen, 1988). However, the rate of abomasal emptying has been shown to be modulated by i.v. infusions of glucose and glucagon (Holtenius et al., 1998), and, therefore, the possibility of the infusions affecting abomasal outflow into the duodenum, duodenal volume, and osmolality cannot be overlooked.
The role of luminal nutrients reaching the ileum has also been shown to influence intestinal nutrient delivery. The release of the peptide hormone Peptide YY from the ileum has been shown to inhibit stomach emptying and pancreatic secretion (Van Citters and Lin, 1999). This phenomenon, termed the ileal brake, is thought to fine-tune nutrient delivery and digestion in the intestine. Onaga et al. (2000) studied the distribution and function of Peptide YY in sheep. Mucosal concentrations of Peptide YY were much less in the sheep compared with those in the rat, and the sheep showed little fluctuation in plasma concentrations of Peptide YY over a 48-h period. In addition, ileal infusion of nutrients or intravenous infusion of CCK also were ineffective in altering plasma Peptide YY concentrations, leaving these authors to conclude that Peptide YY is unlikely to play a role as an ileal brake in sheep. How peptide hormones such as these played a role in the current study remains unclear. There are undoubtedly mechanisms such as this that act in ruminants and using a model with intestinal nutrient infusions is likely to invoke a response from ileal regulatory signals. However, these types of regulatory events tend to govern secretory and digestive events, not the more long-term regulation of digestive enzyme synthesis and secretion.
In this experiment, abomasal casein infusion increased -amylase concentration, as previously observed (Richards et al., 2003). Casein infusion had a very pronounced effect on total -amylase secretion when infused alone; however, when SH + casein were infused together, -amylase secretion was similar to control and SH infusions. Infusing casein with SH also failed to elicit a positive effect on -amylase secretion. These results are similar to those in sheep conducted by Wang and Taniguchi (1998), who found that -amylase secretion (units per milliliter or units per day) was not increased with abomasal infusion of starch + casein compared with control; however, -amylase secretion was decreased with the infusion of starch alone, which is similar to our previous studies (Walker and Harmon, 1995; Swanson et al., 2002b). The results also follow a pattern similar to those obtained by Swanson et al. (2002a) in a similarly designed study. In their experiment, the total -amylase activity (units per pancreas and units per kilogram of BW) and the -amylase mRNA increased in response to 0.6 g/kg of BW–1•d–1 casein infusion alone, but not when casein was infused with 4 g/kg of BW–1•d–1 SH. How casein increases pancreatic -amylase is unclear. How SH interacts to prevent this increase is even more puzzling. Casein did increase plasma insulin concentration but so did SH (Table 3). Other changes in hormonal signals must occur to coordinate these events.
Comparatively little is known about gastrointestinal hormones in ruminants. Aside from insulin and glucagon, probably the most studied has been CCK. Interdigestive pancreatic secretion has been tightly linked to CCK in sheep (Tachibana et al., 1995), and both intraduodenal and intravenous infusions of CCK-8 caused marked increases in pancreatic juice secretion in the calf (Zabielski et al., 1995). Intravenous administration of CCK-8 in sheep has also been shown to increase insulin secretion along with pancreatic secretion of pancreatic juice and -amylase without affecting glucagon secretion (Mineo et al., 1995, 1997). Thus, the increased plasma CCK concentrations seen with SH may be related to the increased plasma insulin concentrations, to the small changes in plasma glucagon, and to the increased pancreatic juice secretion; however, alternative mechanisms must act to reduce the concentration of -amylase seen in this, and our previous studies. Studies in rats have sought to characterize the relationship between CCK and -amylase (Hara et al., 2001). Rats with chronic pancreatic and bile diversion have been shown to hypersecrete CCK, and this is accompanied by decreased pancreatic -amylase. When these rats were given devazepide, a potent CCK(A)-receptor antagonist, the pancreatic -amylase was restored demonstrating that CCK was responsible for the decrease. In the same report, they also determined that feeding a high-carbohydrate diet would increase pancreatic -amylase, demonstrating that dietary mechanisms and CCK act independently and that CCK decreased translational efficiency. Whereas the CCK response helps explain the decreased -amylase seen in ruminants, the results do not explain why cattle do not increase -amylase in response to dietary carbohydrate.
The presence of a CCK-releasing peptide has been well characterized in the intestinal lumen of nonruminants (Wang et al., 2002). This CCK-releasing peptide is secreted into the small intestine, where in the presence of dietary proteins it is spared degradation from intestinal proteases and thereby stimulates secretion of CCK, which in turn stimulates additional pancreatic secretion. This CCK-releasing peptide provides negative feedback for CCK regulation of pancreatic secretion. If such a system functioned in ruminants, it was hypothesized that we would see elevated CCK concentrations in animals receiving casein infusion. However, this was not the case because plasma CCK concentrations were decreased (Table 3). We have previously shown that pancreatic tissue was more responsive to CCK when calves were infused with casein (Swanson et al., 2003), suggesting that receptor numbers or sensitivity to CCK was altered by casein infusion. We found no other examples of lowered plasma CCK concentrations resulting from increased intestinal protein.
Insulin is an important component of pancreatic -amylase regulation in nonruminants (Brannon, 1990). Pancreatic enzyme secretion is decreased in diabetic rats but returns to "normal" with insulin infusion (Otsuki and Williams, 1982). In diabetic sheep, -amylase and lipase secretion decreased and when treated with insulin, lipase secretion returned to normal, but -amylase secretion did not (Pierzynowski and Barej, 1984). The role of insulin in ruminants in regulating -amylase secretion, therefore, is unknown. Both SH and casein infusion increased plasma insulin concentrations in this experiment. Similar trends were not evident for -amylase secretion, suggesting that plasma insulin concentrations may not be directly related to -amylase secretion.
Plasma concentrations of glucagon and PP were examined in this experiment because both are thought to play inhibitory roles in regulating pancreatic secretion in nonruminants (Solomon, 1994) and, therefore, may be involved in the inhibition of pancreatic -amylase secretion observed with increasing postruminal starch flow in ruminants. Although the mechanisms by which glucagon and PP inhibit pancreatic exocrine secretion in nonruminants are not clearly understood, it is known that none of the known peptide inhibitors of pancreatic secretion inhibit secretion from isolated acinar cells in vitro (Debas et al., 1990), suggesting that glucagon and PP do not act directly on the acinar cell to mediate inhibition. It is thought that pancreatic polypeptide acts preferentially to inhibit pancreatic enzyme secretion stimulated by the vagal cholinergic pathway (Owyang, 1994) and that glucagon acts to inhibit secretion stimulated by both hormonal and neural mechanisms (Chey, 1986). Our data suggest, however, that plasma concentrations of PP and glucagon are not increased by SH infusion, which questions their role in inhibiting pancreatic exocrine secretion due to increased postruminal starch flow. In fact, plasma glucagon concentrations were slightly lower in calves receiving SH infusion probably because of increased peripheral glucose concentrations. Knowlton et al. (1998) also reported decreased glucagon concentrations in cows receiving postruminal starch infusion.
Although concentrations of the hormones measured did not mirror the secretion of -amylase, it does not mean that they are not involved in regulating pancreatic secretion. Differences in receptor number and binding or how these hormones interact with other factors may be important in mediating the responses we observed. Swanson et al. (2003) collected pancreatic tissue from calves receiving the same infusion treatments as the present study. The pancreatic tissue was then used in an in vitro model to determine tissue responsiveness to various secretagogues. Tissue from calves receiving casein alone were much more responsive to caerulein (a CCK mimic) than calves receiving SH or SH + casein, suggesting that tissue sensitivity was altered by infusion treatment. Thus, lower plasma concentrations of CCK seen in the present study are not necessarily indicative of a minor role for CCK. Thus, it seems that hormonal regulation occurs at several levels and the apparent relationship between plasma CCK and -amylase secretion observed in the present experiment may not be indicative of the role of CCK in the regulation of -amylase production and secretion. It emphasizes, once again, the complexity of the regulatory mechanisms involved in dietary adaptation of pancreatic exocrine secretion.
Implications
Because postruminal protein infusion did not increase -amylase excretion in the presence of hydrolyzed starch, feeding diets that increase the amount of protein flowing to the small intestine may not be a viable method for increasing pancreatic -amylase secretion and small intestinal starch digestion in calves. Responses observed were not solely the result of changing peripheral plasma concentrations of cholecystokinin, insulin, glucagon, or pancreatic polypeptide. Regulation of digestive enzyme secretion likely involves the coordinated events of hormone secretion and tissue responsiveness to bring about changes in enzyme synthesis and secretion.
Footnotes
1 Published as Publ. No. 03-07-105 of the Kentucky Agric. Exp. Stn. 
2 Current address: Dept. of Animal and Poultry Science, University of Guelph, Guelph Ontario, Canada N1G 2W1.
3 Correspondence: 814 W. P. Garrigus Bldg. (phone: 859-257-7516; fax: 859-257-3412; e-mail: dharmon{at}uky.edu).
Received for publication August 27, 2003. Accepted for publication February 2, 2004.
Literature Cited
Bauer, M. L., D. L. Harmon, K. R. McLeod, and G. B. Huntington. 1995. Adaptation to small intestinal starch assimilation and glucose transport in ruminants. J. Anim. Sci. 73:1828–1838.[Abstract]
Benson, J. A., and C. K. Reynolds. 2001. Effects of abomasal infusion of long-chain fatty acids on splanchnic metabolism of pancreatic and gut hormones in lactating dairy cows. J. Dairy Sci. 84:1488–1500.[Abstract]
Branco, A. F., D. L. Harmon, D. W. Bohnert, B. T. Larson, and M. L. Bauer. 1999. Estimating true digestibility of nonstructural carbohydrates in the small intestine of steers. J. Anim. Sci. 77:1889–1895.
Brannon, P. M. 1990. Adaptation of the exocrine pancreas to diet. Annu. Rev. Nutr. 10:85–105.[Medline]
Chey, W. Y. 1986. Hormonal control of pancreatic exocrine secretion. Page 301 in The Exocrine Pancreas: Biology, Pathobiology, and Diseases. V. L. W. Go, J. D. Gardner, F. P. Brooks, E. Lebenthal, E. P. DiMagno, and G. A. Scheele, ed. Raven Press, New York.
Debas, H. T., S. J. Mulvihill, Y. Goto, and N. W. Bunnett. 1990. Inhibitory mechanisms of the exocrine pancreas. Page 445 in Gastrointestinal Endocrinology: Receptors and Post-Receptor Mechanisms. J. C. Thompson, C. W. Cooper, P. L. Rayford, G. H. Greeley, Jr., P. Singh, and C. M. Townsend, Jr., ed. Academic Press Inc., New York.
Dooley, C. P., and J. E. Valenzuela. 1984. Duodenal volume and osmoreceptors in the stimulation of human pancreatic secretion. Gastroenterology 86:23–27.[Medline]
Geiger, R., and H. Fritz. 1986. Trypsin. Page 119 in Methods of Enzymatic Analysis. H. Bergmeyer, ed. Academic Press, New York.
Hara, H., S. Ohyama, and T. Hira. 2001. Endogenous cholecystokinin plays a role in down-regulation of pancreatic amylase independent of dietary carbohydrate in rats. Regul. Pept. 99:103–110.[Medline]
Holtenius, K., S. O. Jacobsson, and P. Holtenius. 1998. Effects of intravenous infusion of glucose and pancreatic glucagon on abomasal function in dairy cows. Acta Vet. Scand. 39:291–300.[Medline]
Knowlton, K. F., T. E. Dawson, B. P. Glenn, G. B. Huntington, and R. A. Erdman. 1998. Glucose metabolism and milk yield of cows infused abomasally or ruminally with starch. J. Dairy Sci. 81:3248–3258.[Abstract]
Kreikemeier, K. K., D. L. Harmon, R. T. Brandt, Jr., T. B. Avery, and D. E. Johnson. 1991. Small intestinal starch digestion in steers: effect of various levels of abomasal glucose, corn starch and corn dextrin infusion on small intestinal disappearance and net glucose absorption. J. Anim. Sci. 69:328–338.[Abstract]
Li, Y., Y. Hao, J. Zhu, and C. Owyang. 2000. Serotonin released from intestinal enterochromaffin cells mediates luminal non-cholecystokinin-stimulated pancreatic secretion in rats. Gastroenterology 118:1197–1207.[Medline]
Lowry, O. H., N. J. Rosenbrough, A. L. Farr, and R. J. Randall. 1951. Protein measurement with the folin phenol reagent. J. Biol. Chem. 193:265–275.
Merchen, N. R. 1988. Digestion, absorption and excretion in ruminants. Page 172 in The Ruminant Animal: Digestive Physiology and Nutrition. D. C. Church, ed. Prentice-Hall, Englewood Cliffs, NJ.
Mineo, H., N. Iwaki, K. Kogishi, R. Zabielski, T. Onaga, and S. Kato. 1995. Effects of intravenous infusions of cholecystokinin (CCK)-8 on exocrine and endocrine pancreatic secretion in conscious sheep. Comp Biochem. Physiol. Part A Physiol. 111:133–138.
Mineo, H., N. Iwaki, K. Kogishi, T. Onaga, S. Kato, and R. Zabielski. 1997. Effects of proglumide on cholecystokinin-8-induced exocrine and endocrine pancreatic responses in conscious sheep. Comp Biochem. Physiol. Part A Physiol. 118:759–764.
NRC. 1996. Nutrient Requirements of Beef Cattle. 7th ed. National Academy Press, Washington, DC.
Onaga, T., M. Yoshida, H. Inoue, and H. Yokota. 2000. Regional distribution and plasma concentration of peptide YY in sheep. Peptides 21:655–667.[Medline]
Otsuki, M., and J. A. Williams. 1982. Effect of diabetes mellitus on the regulation of enzyme secretion by isolated rat pancreatic acini. J. Clin. Investig. 70:148–156.
Owens, F. N., R. A. Zinn, and Y. K. Kim. 1986. Limits to starch digestion in the ruminant small intestine. J. Anim. Sci. 63:1634–1648.
Owyang, C. 1994. Negative feedback control of exocrine pancreatic secretion: Role of cholecystokinin and cholinergic pathway. J. Nutr. 124:1321S–1326S.
Pierzynowski, S., and W. Barej. 1984. The dependence of exocrine pancreatic secretion on insulin in sheep. Q. J. Exp. Phys. 69:35–39.
Richards, C. J., K. C. Swanson, S. J. Paton, D. L. Harmon, and G. B. Huntington. 2003. Pancreatic exocrine secretion in steers infused post-ruminally with casein and corn starch. J. Anim. Sci. 81:1051–1056.
Slein, M. W. 1963. D-Glucose determinations with hexokinase and glucose-6 phosphate dehydrogenase. Page 117 in Methods of Enzymatic Analysis. H. U. Bergmeyer, ed. Academic Press, New York.
Solomon, T. E. 1994. Control of exocrine pancreatic secretion. Page 1499 in Physiology of the Gastrointestinal Tract. L. R. Johnson, ed. Raven Press, New York.
St. Jean, G., D. L. Harmon, J. P. Peters, and N. K. Ames. 1992. Collection of pancreatic exocrine secretions by formation of a duodenal pouch in cattle. Am. J. Vet. Res. 53:2377–2380.[Medline]
Swanson, K. C., and D. L. Harmon. 2002. Dietary influences on pancreatic alpha-amylase expression and secretion in ruminants. Page 515 in Biology of the Intestine in Growing Animals. R. Zabielski, P. C. Gregory, and B. Westrom, ed. Elsevier Science, New York.
Swanson, K. C., J. C. Matthews, C. A. Woods, and D. L. Harmon. 2002a. Post-ruminal administration of partially hydrolyzed starch and casein influences pancreatic -amylase expression in calves. J. Nutr. 132:376–381.
Swanson, K. C., J. C. Matthews, C. A. Woods, and D. L. Harmon. 2003. Influence of substrate and/or neurohormonal mimic on in vitro pancreatic enzyme release from calves postruminally infused with partially hydrolyzed starch and/or casein. J. Anim. Sci. 81:1323–1331.
Swanson, K. C., C. J. Richards, and D. L. Harmon. 2002b. Influence of abomasal infusion of glucose or partially hydrolyzed starch on pancreatic exocrine secretion in beef steers. J. Anim. Sci. 80:1112–1116.
Tachibana, S., T. Onaga, H. Mineo, and S. Kato. 1995. Role of endogenous CCK in regulation of interdigestive pancreatic exocrine secretion in sheep (Ovis aries). Comp. Biochem. Physiol. Part A Physiol. 112:103–109.
Theurer, C. B. 1986. Grain processing effects on starch utilization by ruminants. J. Anim. Sci. 63:1649–1662.
Van Citters, G. W. and H. C. Lin. 1999. The ileal brake: A fifteen-year progress report. Curr. Gastroenterol. Rep. 1:404–409.[Medline]
Walker, J. A., C. R. Krehbiel, D. L. Harmon, G. St. Jean, W. J. Croom, Jr., and W. M. Hagler, Jr. 1994. Effects of slaframine and 4-diphenylacetoxy-N-methylpiperidine methiodide (4DAMP) on pancreatic exocrine secretion in the bovine. Can. J. Physiol. Pharmacol. 72:39–44.[Medline]
Walker, J. A., and D. L. Harmon. 1995. Influence of ruminal or abomasal starch hydrolysate infusion on pancreatic exocrine secretion and blood glucose and insulin concentrations in steers. J. Anim. Sci. 73:3766–3774.[Abstract]
Walker, J. A., and D. L. Harmon. 1996. Technical note: A simple, rapid assay for -amylase in bovine pancreatic juice. J. Anim. Sci. 74:658–662.[Abstract]
Wang, Y., V. Prpic, G. M. Green, J. R. Reeve, Jr., and R. A. Liddle. 2002. Luminal CCK-releasing factor stimulates CCK release from human intestinal endocrine and STC-1 cells. Am. J. Physiol. Gastrointest. Liver Physiol. 282:G16–G22.
Wang, X., and K. Taniguchi. 1998. Activity of pancreatic digestive enzymes in sheep given abomasal infusion of starch and casein. Anim. Sci. Technol. 69:870–874.
Wirnt, R. 1986. Chymotrypsin. Page 1013 in Methods of Enzymatic Analysis. H. Bergmeyer, ed. Academic Press, New York.
Zabielski, R., T. Onaga, H. Mineo, S. Kato, and S. G. Pierzynowski. 1995. Intraduodenal cholecystokinin octapeptide (CCK-8) can stimulate pancreatic secretion in the calf. Int. J. Pancreatol. 17:271–278.[Medline]
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