Comparison of the Kinetics of Pancreatic Secretion and Gut Regulatory Peptides in the Plasma of Preruminant Calves Fed Milk or Soybean Protein

Comparison of the Kinetics of Pancreatic Secretion and Gut Regulatory Peptides in the Plasma of Preruminant Calves Fed Milk or Soybean Protein G. LE DREAN,* I. LE HUEROU-LURON,*,1 M. GESTIN,* V. ROME,* M. PLODARI,* C. BERNARD,† J. A. CHAYVIALLE,† and P. GUILLOTEAU* *Institut National de Recherche Agronomique, Laboratoire du Jeune Ruminant, 65, rue de Saint-Brieuc, 35042 Rennes, France †Institut National de la Sante ´ et de la Recherche Me´dicale, Unite´ de Recherches de Physiopathologie Digestive, Hoˆpital E. Herriot, 69374 Lyon, Cedex, France

ABSTRACT Exocrine secretion from the pancreas and concentrations of cholecystokinin, gastrin, secretin, and somatostatin in plasma were measured in relation to feeding in 70- to 120-d-old preruminant calves fed either a milk diet or a soybean diet. Pancreatic fluid was continuously collected, measured, and reintroduced in catheterized calves. Blood samples were withdrawn for measurements of gut regulatory peptide concentrations in plasma. A slight increase in outflow of pancreatic fluid was observed 30 min before the milk diet was introduced but not before the soybean diet was fed. In contrast, concentrations and outflows of protein and trypsin immediately after feeding were higher when calves were fed the soybean diet. Overall, during the first 5 h postfeeding, the outflow of pancreatic fluid was 40% higher when the milk diet was fed than when the soybean diet was fed. No difference in outflow of protein was observed, but that of trypsin was 82% higher when the soybean diet was fed. This enhanced enzyme secretion could have been related to the increased plasma concentrations of gastrin and cholecystokinin after the soybean diet was fed. Secretin release was less in calves fed the milk diet that in calves fed the soybean diet during the first 2 h postfeeding, suggesting that this gut peptide along with gastrin and cholecystokinin, contributed to the stimulation of enzyme secretion. Plasma gut regulatory peptides could be influenced by the soybean diet, which does not coagulate in the stomach, inducing faster gastric emptying of protein and fat, and by the chemical form of protein from the soybean diet and the lower susceptibility of these proteins to protease compared with casein. However,

Received March 18, 1997. Accepted December 9, 1997. 1Reprint requests. 1998 J Dairy Sci 81:1313–1321

the resulting enhancement of pancreatic trypsin secretion and activity seemed to be insufficient to increase the digestibility of soybean protein up to a level similar to that of milk. ( Key words: pancreatic exocrine secretion, gut regulatory peptides, calf, dietary protein) Abbreviation key: CCK = cholecystokinin, MD = milk diet, SBD = soybean diet. INTRODUCTION Soybean protein is commonly substituted for part of the milk protein in milk replacers fed to preruminant calves. However, the replacement of a large part of protein from milk with soybean concentrates depresses nutrient digestibility and calf performance (13, 31). These results could be partially due to a faster gastric emptying rate for noncasein protein and fat because of the absence of coagulation (30). Moreover, modifications in the plasma concentration of several regulatory peptides of the gut were observed ( 6 ) . Prefeeding concentrations of secretin were lower when a soybean diet ( SBD) was fed than when a milk diet ( MD) was fed, and, 1 h after feeding, the concentration of cholecystokinin ( CCK) was higher. Similar and simultaneous patterns of exocrine secretion from the pancreas and some concentrations of gut regulatory peptides in plasma have been established in calves fed a MD (15). Parallel profiles for the outflow of fluid from the pancreas and plasma secretin, as well as concentrations of protein, trypsin, gastrin, and CCK, suggest that these gut peptides are important in the regulation of pancreatic secretion in the calf. However, involvement of these peptides in pancreatic adaptation to dietary protein is still unclear, and the kinetics of pancreatic outflow and concentration of gut regulatory peptides in plasma postfeeding have not yet been studied.

1313

1314

LE DREAN ET AL.

In the present experiment, the kinetics of exocrine secretion from the pancreas were analyzed in calves fed diets based exclusively on milk protein or soybean and whey protein. The soybean concentrate was extracted with alcohol to denature its antinutritional factors and to limit digestive problems. The concentrations of four plasma gut regulatory peptides (i.e., gastrin, CCK, secretin, and somatostatin) involved in digestive processes ( 3 3 ) were simultaneously measured at short intervals around the time that meals were fed. MATERIALS AND METHODS Calves and Diets Treatments and experiments were conducted according to European Union regulations concerning the protection of experimental animals. The experiment was carried out on 10 Holstein-Friesian male calves between 70 and 120 d of age. All calves were given colostrum (25 g/kg of live weight per meal) during the first 2 d of life and then received a milk substitute diet based on skim milk, whey powders, and tallow ( M D ) until 65 d of age (Table 1). From d 66, calves were fed either the MD or a milk substitute diet, the protein of which was provided by an alcoholextracted soybean concentrate (73.6%) and whey powder (SBD). Antitryptic activity measured in the concentrate by the method of Liu and Markakis ( 2 1 ) was only 7.4 trypsin units inhibited/mg of protein. As determined by the method of Tukur et al. (32), antigenic activity was very low, and other antinutritional factors, such as lectins, were not detected. During the entire experimental period, each calf received each diet successively and randomly during two 10-d periods ( 4 d of transition, 3 d of adaptation, and 3 d of measurements). Calves were fed twice daily at 0830 and 1630 h. The DMI was 66 g/kg of live weight0.75 per d. Collection of Pancreatic Fluid Two weeks prior to the experiment, 4 calves were fitted with two permanent cannulas (pancreatic duct and duodenum) under halothane anesthesia as previously described (15). Throughout each experiment, pancreatic fluid was continuously collected, measured, and reintroduced (92%) into the duodenum by means of a pump that extracted a constant proportion ( 8 % ) of juice at 15-min intervals during 8.5 h (from 1.5 h before to 7.0 h after the 0830-h meal) and one sample for the remaining 15.5 h of the day. Samples were immediately transferred into a fraction collector at 4°C, and aliquots were stored at –20°C. The fluid was analyzed to determine protein concentration Journal of Dairy Science Vol. 81, No. 5, 1998

( 2 2 ) and trypsin activity (12). Units of trypsin activity were expressed as nanomoles of p-nitroaniline released per minute at 20°C. For the MD, each calf underwent one experiment; for the SBD, each calf underwent three experiments, except for 1 calf that underwent only two experiments. Therefore, 4 and 11 sets of data were analyzed when calves were fed the MD and SBD, respectively. Mean live weights of calves during the experiment were 110 ± 15 and 119 ± 16 kg when the calves were fed the MD and SBD, respectively ( X ± SE; n = 4). Gut Regulatory Peptides in Plasma Six Holstein-Friesian male calves were divided in two groups of 3 calves each that received the MD or

TABLE 1. Composition of milk replacers. Milk diet

Soybean diet (%)

Ingredient Fat1 Skim milk powder Whey powder Whey protein concentrate Pregelatinized starch Soybean concentrate2 Lactose Minerals, trace elements, vitamins, and synthetic AA3 Composition Protein ( N × 6.25) Fat N-Free extract Ash Ca P 1Tallow

21.2 57.0 13.6 ... 3.7 ... ...

19.4 ... 38.8 2.3 2.0 24.5 9.0

4.5

4.0 ( % of DM)

22.2 20.6 49.9 7.3 0.91 0.78

21.1 21.1 49.4 8.4 1.05 1.18

(78%) and coconut oil (22%). 70 g of protein/100 g of DM and was prepared from dehulled soybeans by hexane extraction of oil and hot aqueous ethanol extraction of sucrose and a-galactosides. 3Composition (per 100 g of milk substitute) in the milk diet: 0.36 mg of retinol, 7.5 mg of cholecalciferol, 5 mg of a-tocopheryl acetate, 0.25 mg of menadione, 0.7 mg of thiamin, 0.7 mg of riboflavin, 0.6 mg of pyridoxine, 0.12 mg of nicotinic acid, 10 mg of ascorbic acid, 0.6 mg of folic acid, 6 mg of cyanocobalamin, 60 mg of biotin, 0.6 mg of pantothenic acid, 0.12 g of choline, 0.24 g of Ca, 0.6 mg of Cu, 9.5 mg of Fe, 20 mg of I, 3.1 mg of K, 66.4 mg of Mg, 5.2 mg of Mn, 0.121 g of Na, 0.18 g of P, 8 mg of Zn, 8 mg of bacitracin, 1 g of sorbitol, 0.124 g of L-lysine·HCl, and 0.167 g of DL-methionine. Composition (per 100 g of milk substitute) in the soybean diet: 0.39 mg of retinol, 7.2 mg of cholecalciferol, 4.76 mg of a-tocopheryl acetate, 0.24 mg of menadione, 0.66 mg of thiamin, 0.66 mg of riboflavin, 0.57 mg of pyridoxine, 1.14 mg of nicotinic acid, 9.5 mg of ascorbic acid, 60 mg of folic acid, 6 mg of cyanocobalamin, 6 mg of biotin, 0.57 mg of pantothenic acid, 0.129 g of choline, 0.7 g of Ca, 0.33 mg of Cu, 14 mg of I, 4.6 mg of K, 7 mg of Mg, 3.2 mg of Mn, 0.43 g of P, 8 mg of Zn, 0.28 g of Cl, 8 mg of bacitracin, 0.476 g of sorbitol, 0.398 g of L-lysine·HCl, and 0.227 g of DL-methionine. 2Contained

1315

SOYBEAN PROTEIN AND PANCREATIC SECRETION

the SBD successively as described previously. Calves were fitted with a jugular vein catheter. Blood samples were collected into a tube containing heparin (500 IU/ml) and aprotinin (10,000 IU/ml) at 90, 60, 45, 30, and 15 min before the meal and at 5, 15, 30, 60, and 90 min after the meal. Afterward, blood samples were taken every hour until 7.5 h after the 0830-h meal. Plasma samples were stored at –20°C. Blood was collected twice on each calf for each diet, and data were pooled across days (e.g., at 76 and 78 d of age and at 90 and 92 d of age). During this experimental period, calves weighed 107 ± 5 and 105 ± 5 kg when fed the MD and SBD, respectively. Plasma peptide concentrations were measured by radioimmunoassay. Details of the analytical methods have been previously reported ( 1 5 ) except that in the present study the carbon dextran extraction method was used instead of the double-antibody technique. Results were expressed as femtomoles of equivalent of standard per milliliter of plasma.

time was made by contrast to the basal value in a model including day and calf as factors. The general linear model procedure of SAS ( 2 6 ) was applied to the statistical evaluation of the data, using analysis of variance on repeated measures. RESULTS Results of pancreatic secretion were expressed as absolute values (Table 2 ) and as percentages of the basal value represented by the mean of the first three collected samples (Figures 1 and 2). This expression made it possible to analyze the effect of the meal itself on pancreatic secretion between the two diets. For concentrations of gut regulatory peptides in plasma, absolute values are reported in the Table 3, and the relative data (Figure 3 ) refer to the mean of the first two collected samples (from –1.5 to –1.0 h before the 0830-h meal), which was considered to be the basal value. Two groups of calves were voluntarily used separately for analysis to avoid disturbances in pancreatic secretion during blood collection.

Statistical Analysis For comparison between diets, a split-plot design, including diet, calf, and day as factors, was used in all analyses. The interaction of calf and diet was the error term used in post hoc t tests to separate differences between means. For comparison within a group (response to the meal), analyses were made by diet. For the MD, time was the single factor of the model, and differences between means were separated by contrast to the basal value. For the SBD, analysis of

Kinetics of the Secretion of Pancreatic Fluid Total daily secretion of pancreatic fluid was not affected by source of dietary protein (Table 2). In contrast, prefeeding (–1.5 to 0 h ) and postfeeding ( 0 to 5.0 h ) outflows of fluid were 40% lower when the SBD was fed than when the MD was fed. When the MD was fed, the outflow of pancreatic fluid slightly increased during the 30 min preceding

TABLE 2. Effect of dietary protein source on outflow of pancreatic fluid, protein, and trypsin at different periods relative to time of feeding. Outflow Time relative to feeding1 (h) –1.5 –1.5 –1.5 0 to 0 to 0 to

Pancreatic fluid MD2 X

to 22.5 to 7 to 0 0.5 2.0 5.0

Protein

SBD3

MD

(ml/h per kg of LW4) SE X SE

0.51 0.52 0.93a 0.49 0.32 0.44a

0.08 0.12 0.26 0.06 0.03 0.04

0.49 0.41 0.52b 0.55 0.29 0.26b

0.07 0.06 0.14 0.09 0.04 0.03

X 3.13 2.37 2.84 2.39 1.96 1.94

Trypsin

SBD

MD

(mg/h per kg of LW) SE X SE 0.54 0.33 0.26 0.70 0.41 0.43

2.74 2.98 2.75 4.66 3.00 2.70

0.36 0.49 0.87 0.84 0.28 0.27

X 1150 973d 1062 709d 645b 817b

SBD (U/h per kg of LW) SE X SE 303 61 58 127 110 55

1219 1477c 1196 2093c 1571a 1485a

253 266 353 529 220 230

a,bMeans

within a row within a category with different superscripts differ ( P < 0.05). within a row within a category with different superscripts differ ( P < 0.01). 1The meal was fed at 0 h. 2Milk diet. 3Soybean diet. 4Live weight. c,dMeans

Journal of Dairy Science Vol. 81, No. 5, 1998

1316

LE DREAN ET AL.

the meal (Figure 1). Then, outflow sharply decreased by 80% during the first 30 min, remained low during the next 4 h, and increased thereafter to the basal

value that was reached 5 h after the meal. When the SBD was fed, outflow of the pancreatic fluid did not change before feeding, increased by 47% during the

Figure 1. Mean values ( n = 4 ) for outflow of pancreatic fluid, protein concentration, and outflow of protein expressed as percentages of the basal value (mean of the first three values). The basal values for outflow of pancreatic fluid, protein concentration, and outflow of protein were 22.8 ml/15 min, 3.2 mg/ml, and 4.9 mg/min when the milk diet ( M D ) was fed and 15.0 ml/15 min, 5.3 mg/ml, and 5.3 mg/min when the soybean diet (SBD) was fed, respectively. Legend: measurements when the MD was fed ( o) ; measurements when the SBD was fed ( ⁄) . *Differences between measurements when calves were fed the MD and SBD at the same hour ( P < 0.05). aDifference from basal values when calves were fed the MD ( P < 0.05); bdifference from basal values when calves were fed the SBD ( P < 0.05).

Figure 2. Mean values ( n = 4 ) for the concentration of pancreatic trypsin, specific activity of trypsin, and outflow of trypsin expressed as percentages of the basal value (mean of the first three values). The basal values for concentration of trypsin, specific activity of trypsin, and outflow of trypsin were 1084 U/ml, 342 U/ mg of protein, and 1645 U/min when the milk diet ( M D ) was fed and 2390 U/ml, 459 U/mg of protein, and 2397 U/min when the SBD was fed, respectively. Legend: measurements when the MD was fed ( o) ; measurements when the SBD was fed ( ⁄) . *Differences between measurements when calves were fed the MD and SBD at the same hour ( P < 0.05). aDifference from basal values when calves were fed the MD ( P < 0.05); bdifference from basal values when calves were fed the SBD ( P < 0.05).

Journal of Dairy Science Vol. 81, No. 5, 1998

1317

SOYBEAN PROTEIN AND PANCREATIC SECRETION

first 15 min after the meal, and decreased rapidly to 43% of the basal value. This level remained low for 4 h after the meal and then increased slowly to a value that was 105% higher than the basal value at 7 h after the meal. Pancreatic Protein and Trypsin Secretion Total daily outflows of protein and trypsin were not affected by change in dietary protein (Table 2). However, during the –1.5- to 7.0-h period, trypsin outflow was higher when the SBD was fed because of the high postfeeding secretion than when the MD was fed. Such a high increase was not observed for the outflow of protein during the same period (Table 2). When the MD was fed, protein concentration increased immediately after the meal by 45% (Figure 1), was 190% higher than the basal value at 1 h postfeeding, and remained higher during the 7 h postfeeding. When the SBD was fed, a similar pattern was observed but at a higher level. Protein concentration sharply increased after the meal and was 280% higher than the basal value at 1 h postfeeding. The basal value was reached at 6 h after the meal. When the MD was fed, the outflow of protein from the pancreas behaved as did the outflow of pancreatic fluid. The outflow of pancreatic protein slightly increased during the last 30 min before the meal, decreased by 70% during the 30 min postfeeding, and increased to the basal value at 3 h after the meal. When the SBD was fed, as was true for the outflow of pancreatic fluid, protein secretion immediately increased by 210% after the meal and then decreased to the basal value that was reached 1 h after the meal. Trypsin concentration and outflow (Figure 2 ) fol-

lowed patterns similar to those of protein concentration and outflow. Postfeeding differences observed between the two diets were greater for trypsin than for protein. Trypsin concentration increased by 140 and 280%, respectively, at 1 h after the MD and SBD were fed (Figure 2). During the first 2 h postfeeding, trypsin outflow was 143% higher when the SBD was fed than when the MD was fed; protein outflow was only 53% higher (Table 2). The pattern of the specific activity of trypsin was not affected by the nature of the diet except during the 1st h postfeeding. Kinetics of Gut Regulatory Peptides in Plasma In plasma, the gut regulatory peptide concentrations of gastrin, CCK, secretin, and somatostatin were not affected by dietary protein (Table 3). Postfeeding secretin was not depressed when the SBD was fed in contrast to secretin depression when the MD was fed. For both groups of calves, the meal induced significant changes in concentrations of gut regulatory peptides in plasma except for the concentration of somatostatin (Figure 3). When the MD was fed, gastrin and CCK concentrations in plasma increased immediately after feeding up to 177 and 193% of the basal value, respectively. At the end of the experimental period, the gastrin concentrations were still higher than the basal value. In contrast, the secretin concentrations were 45% lower than the basal value between 0.5 and 1.0 h postfeeding. When the SBD was fed, postfeeding patterns of gastrin and CCK concentration were similar but more emphasized than those recorded when the MD was fed. The highest variations were 275 and 250% of the basal

TABLE 3. Gut regulatory peptide concentrations (femtomoles per milliliter) in plasma at different periods relative to time of feeding. CCK1

Gastrin

Time relative to feeding2

MD3

(h) –1.5 to –1.0 –0.75 to –0.25 0.08 to 0.5 1.0 to 4.5 5.5 to 7.5

X 21.0 17.6b 35.2c 37.4c 29.4a

SBD4 SE 3.6 2.7 5.6 5.3 5.1

X 18.2 19.3 34.3c 43.6c 23.8

MD SE 1.9 2.6 2.9 3.2 3.8

X 6.45 5.55a 10.6c 9.83c 6.57

Secretin

SBD SE 0.9 0.7 1.9 1.3 0.7

X 4.45 4.94 8.13c 10.3c 7.47c

MD SE 0.6 0.9 0.8 1.9 1.2

X 4.90 4.60 3.54a 5.29 5.13

SE 0.7 0.7 0.6 1.6 1.2

Somatostatin

SBD

MD

X SE 5.37 1.0 5.27 1.4 4.40 1.1 5.96 0.6 5.45 0.2

X 14.6 14.0 13.6 15.1 20.9a

SBD SE 3.8 4.2 4.4 2.8 1.6

X 11.5 13.5 12.6 16.6b 18.6c

SE 1.5 1.6 2.4 1.0 2.0

aMeans

within a category with this superscript differ ( P < 0.1) from the basal value (–1.5 to –1.0 h). within a category with this superscript differ ( P < 0.05) from the basal value (–1.5 to –1.0 h). cMeans within a category with this superscript differ ( P < 0.01) from the basal value (–1.5 to –1.0 h). 1Cholecystokinin. 2The meal was fed at 0 h. 3Milk diet. 4Soybean diet. bMeans

Journal of Dairy Science Vol. 81, No. 5, 1998

1318

LE DREAN ET AL.

Figure 3. Mean values ( n = 6 ) for plasma gastrin, cholecystokinin (CCK), secretin, and somatostatin expressed as percentages of the basal value (mean of the first two values). Legend: measurements when the milk diet ( M D ) was fed ( o) ; measurements when the soybean diet (SBD) was fed ( ⁄) . *Differences between measurements when calves were fed the MD and SBD at the same hour ( P < 0.05). aDifference from basal values when calves were fed the MD ( P < 0.05); bdifference from basal values when calves were fed the SBD ( P < 0.05).

value for gastrin and CCK, respectively. At 5.5 h after the meal, gastrin concentration in plasma decreased to the same concentration (higher than the basal value) that was observed when the MD was fed. During the entire postfeeding period, the CCK concentration in plasma remained higher than the basal value. Contrary to the concentration when the MD was fed, the concentration of secretin significantly increased 30 min after the meal up to 140% of the basal value at 1.5 h postfeeding. DISCUSSION Dietary Protein and Pancreatic Secretion When the MD was fed, daily pancreatic fluid and secretions of protein and trypsin were similar to our previous results ( 1 5 ) and results reported in the Journal of Dairy Science Vol. 81, No. 5, 1998

literature (1, 11, 25). In contrast, pancreatic enzyme response to dietary protein was more controversial. A reduction in the secreted trypsin activity and low variations in protein outflow have been reported for calves fed diets containing soybean products (4, 28). In the present study, trypsin activity and outflow were higher when calves were fed the SBD. However, methods used in the previous experiments to collect pancreatic fluid did not respect physiological conditions. Pancreatic fluid was not simultaneously reintroduced in contrast with the present study. Diversion of the pancreatic fluid could account for modifying digestive events (e.g., the pH of intestinal contents). Variations in pancreatic response observed between studies could have also been due to the use of differently processed soybean products and their level of incorporation in milk substitutes (17). In the present study, we clearly demonstrated that a nonantigenic soybean concentrate that is free from antinutritional factors can modify pancreatic secretion patterns, especially that of trypsin. The pancreas seemed to adapt its secretion to the presence of soybean protein in the diet by increasing trypsin activity and outflow. Efird et al. ( 3 ) also reported a greater secretion of trypsin and chymotrypsin by pigs fed soybeans than by pigs fed milk. Those researchers ( 3 ) clearly established a relationship between a decrease in the activities in the pancreatic tissue and an increase in the intestinal contents when a SBD was fed. Gastric emptying of protein is faster when a SBD is fed than when a MD is fed (3, 30), and soybean has a greater buffering effect on gastric and duodenal pH than does casein (23). These effects may result in less proteolytic activity in the stomach and the release of more intact protein into the small intestine, which may transiently affect pancreatic protease secretion as we observed for trypsin in the present experiment. In a previous work ( 7 ) , we showed that duodenal trypsin activity in relationship to the protein that enters the duodenum is lower when a SBD is fed than when a MD is fed. Thus, the low activity of trypsin in duodenal contents when a SBD was fed ( 7 ) was not related to the decrease in the outflow of pancreatic trypsin. The enzyme seemed to be inactivated in the digesta, probably by the formation of complexes with trypsin-resistant soybean protein. Despite the greater proteolytic activity in the pancreatic fluid of calves fed SBD, the digestibility of total N (77%) was not as high as that obtained when the MD was fed (93%) [(7); I. Le Hue¨rou-Luron and P. Guilloteau, 1998, personal communication]. Estimated true digestibility is low for some AA, such as Leu, Ala, Asp, and Gly, suggesting that polypeptides that are rich in these AA from soybean protein could

SOYBEAN PROTEIN AND PANCREATIC SECRETION

be harder to digest by preruminant calves, even in a partially hydrolyzed soybean isolate (29). Moreover, the chemical form (folding) of protein in soybean products may be an important factor in their digestibility because it would lead to a higher resistance to proteolysis (10). Dietary Protein and Gut Regulatory Peptides in Plasma Basal values of CCK and gastrin were similar when MD or SBD was fed, and variations in CCK and gastrin responses to the meal were higher when the SBD was fed. A previous study ( 6 ) also reported higher concentrations of plasma CCK in calves receiving a soybean concentrate than in calves receiving a MD. The concentration of gastrin postfeeding was also higher with whey protein than with milk protein ( 8 ) . In preruminant calves, postfeeding changes in plasma CCK and gastrin could be related to the ability of dietary protein to coagulate in the abomasum and, consequently, the pattern of gastric emptying. In a previous study on preruminant calves ( 9 ) , we showed that when a SBD was fed, gastric emptying of fat was fourfold higher than when a MD was fed; this effect was observed as soon as 30 min after the meal and persisted over 7 h postfeeding. Intestinal fat is a strong stimulant for CCK release (27). A higher rate of gastric emptying of fat when the SBD was fed could explain the immediately higher increase in plasma CCK postfeeding compared with that occurring after the MD was fed. Protein, peptides, AA, and amines are strong stimulants for gastrin release ( 2 ) . During the first 2 h after the meal, plasma gastrin concentration was similar when either the MD or the SBD was fed, as was the rate of gastric emptying of total N measured in our previous work ( 9 ) . Between 2 and 4 h postfeeding, a peak in gastrin concentration occurred when the SBD was fed; the rate of gastric emptying of total N was reported to increase during the same period ( 9 ) . Thus, patterns of gastric emptying of fat and protein in noncoagulating diets, measured previously ( 9 ) , seemed to be in accordance with the postfeeding variations in plasma CCK and gastrin observed here. The decrease in plasma gastrin concentration was probably due to the feedback control of gastric acid secretion on gastrin release. Secretin release is considered to be stimulated when the duodenal pH is <4.5 (18). The higher secretin release observed when the SBD was fed might have been related to a higher duodenal acidification because of faster gastric emptying ( 9 ) . No marked effect of feeding was noticed for somatostatin, regardless of the

1319

dietary protein, as has previously been reported for fish, whey, and soybean proteins ( 8 ) . Moreover, somatostatin probably acts as a paracrine regulator of CCK secretion via a mechanism similar to the interaction between gastric D (somatostatin) and G (gastrin) cells (20). Therefore, a physiological action of this peptide may not be entirely detected via a peripheral plasma assay. Dietary Protein, Pancreatic Secretion, and Gut Regulatory Peptides For calves fed milk, parallel patterns have been established for the outflow of pancreatic fluid and secretin and for protein, trypsin, CCK, and gastrin concentrations (15). In the present experiment, similar patterns were produced by the two diets, except for secretin. Plasma secretin postfeeding was initially less depressed and then increased when the outflow of fluid was decreased when the SBD was fed. Lack of the cephalic phase when the SBD was fed was noteworthy because this phase has been previously described in calves fed milk (15). No simultaneous variation of the gut peptides assayed was observed. This result was in agreement with the results of Pierzynowski et al. (24), who suggested that the cephalic phase in preruminant calves was vagally dependent. The present study showed that changes in dietary composition and, therefore, in sensory aspects of the meal may have different effects on pancreatic secretion. When the SBD was fed, protein concentration and outflow, especially those of trypsin, were higher than when the MD was fed. Infusion of CCK or gastrin strongly stimulated protein and trypsin secretions (16), and higher variations in plasma concentration of these two peptides when the SBD was fed could explain the enhanced response in enzyme secretion. As observed with trypsin inhibitors in rats ( 5 ) , undigested soybean protein may form a complex with duodenal trypsin that stimulates CCK release by activation of a CCK-releasing factor that is sensitive to trypsin. The CCK would in turn stimulate trypsin secretion. Gastrin and CCK share a common pancreatic receptor, the CCK-B/gastrin receptor, which is the predominant receptor over the CCK-A receptor in preruminant calves from 28 d of age (19). In addition to the higher increase in plasma CCK and gastrin concentrations after the SBD was fed, pancreatic CCK-A and CCK-B/gastrin receptors may be directly influenced by dietary protein. Expression of those receptors in calves that are receiving different diets might be studied to correlate with the release of gut regulatory peptides. Secretin also appeared to be Journal of Dairy Science Vol. 81, No. 5, 1998

1320

LE DREAN ET AL.

sensitive to change in dietary protein because postfeeding variations were reversed between the two diets; however, the mechanisms involved remain difficult to explain. The decreased secretion of pancreatic fluid postfeeding that was observed when the MD and the SBD were fed cannot be related to plasma secretin as previously proposed (15). A significant fluctuation of secretin with duodenal migrating myoelectric complex and periodic pancreatic secretion has been observed (35). However, postfeeding disruption of migrating myoelectric complex, which results in a long period of irregular spiking activity, has been found to be similar ( 1 to 1.5 h ) for calves fed milk and calves fed soybeans (14). Secretin has been shown to stimulate the output of protein and trypsin in the preruminant calf (34). Thus, secretin could contribute with gastrin and CCK to the higher outflow of trypsin postfeeding that was observed when SBD was fed compared with that when the MD was fed. To conclude, the postfeeding release of CCK, gastrin, and secretin is probably sensitive to dietary protein of preruminant calves and could be responsible for changes in protein and trypsin concentrations in pancreatic fluid observed between diets after the meal. These variations in concentrations of gut regulatory peptides were affected by the lack of coagulation in the calf abomasum, which induces a faster gastric emptying, and by the chemical form of the noncasein protein and the lower susceptibility of these proteins than of casein to protease. However, the resulting stimulation of pancreatic trypsin concentration and activity appeared to be insufficient to increase the digestibility of soybean N to a level similar to that of milk. ACKNOWLEDGMENTS The authors thank J. Quillet for collecting the bibliographical information; L. Delaby for statistical support; G. Savary, S. Boussion, M. Lesne´, and S. Ten for their technical assistance; and the team of translators from Rennes 2 University (Rennes, France) for the English revision of the manuscript. REFERENCES 1 Davicco, M. J., J. Lefaivre, P. Thivend, and J. P. Barlet. 1979. Exocrine pancreatic secretion in preruminant milk-fed calves. Ann. Rech. Vet. 10:428–430. 2 Del Valle, J., and T. Yamada. 1990. Amino-acids and amines stimulate gastrin release from canine antral G-cells via different pathways. J. Clin. Invest. 85:139–143. 3 Efird, R. C., W. D. Armstrong, and D. L. Herman. 1982. The development of digestive capacity in young pigs: effects of weaning and dietary treatment. J. Anim. Sci. 55:1370–1379. Journal of Dairy Science Vol. 81, No. 5, 1998

4 Gorrill, A.D.L., J. W. Thomas, W. E. Stewart, and J. L. Morrill. 1967. Exocrine pancreatic secretion by calves fed soybean and milk protein diets. J. Nutr. 92:86–92. 5 Green, G. M., V. H. Levan, and R. A. Liddle. 1986. Interaction of dietary protein and trypsin inhibitor on plasma cholecystokinin and pancreatic growth in rats. Pages 123–132 in Nutritional and Toxicological Significance of Enzyme Inhibitors in Foods. M. Friedman, ed. Plenum, New York, NY. 6 Guilloteau, P., T. Corring, J. A. Chayvialle, C. Bernard, J. W. Sissons, and R. Toullec. 1986. Effect of soya protein on digestive enzymes, gut hormone and anti-soya antibody plasma levels in the preruminant calf. Reprod. Nutr. Dev. 26:717–728. 7 Guilloteau, P., and I. Le Hue¨rou-Luron. 1996. Exocrine pancreatic secretions and their regulations in the preruminant calf. Pages 169–189 in Veal Perspectives to the Year 2000. Fe´de´ration de la Vitellerie Franc¸aise, Paris, France. 8 Guilloteau, P., I. Le Hue¨rou-Luron, J. A. Chayvialle, R. Toullec, R. Zabielski, and J. W. Blum. 1997. Gut regulatory peptides in young cattle and sheep. J. Vet. Med. Ser. A 44:1–23. 9 Guilloteau, P., R. Toullec, D. Sauvant, and J. L. Paruelle. 1979. Utilisation des prote´ines par le veau pre´ruminant a` l’engrais. VII. Influence du remplacement des prote´ines du lait par celles du soja ou de la fe´verole sur l’e´vacuation gastrique. Ann. Zootech. (Paris) 28:1–17. 10 Ikeda, K., Y. Matsuda, A. Katsumaru, M. Teranishi, T. Yamamoto, and M. Kishida. 1995. Factors affecting protein digestibility in soybean foods. Cereal Chem. 72:401–405. 11 Khorasani, G. R., L. Ozimek, W. C. Sauer, and J. J. Kennelly. 1989. Substitution of milk protein with isolated soy protein in calf milk replacers. J. Anim. Sci. 67:1634–1641. 12 Laine´, J., M. Beattie, and D. Lebel. 1993. Simultaneous kinetic determinations of lipase, chymotrypsin, trypsin, elastase, and amylase on the same microtiter plate. Pancreas 8:383–386. 13 Lalle`s, J. P. 1993. Nutritional and antinutritional aspects of soybean and field pea proteins used in veal calf production. A review. Livest. Sci. Prod. 34:181–202. 14 Lalle`s, J. P., D. Benkredda, and R. Toullec. 1995. Influence of soya antigen levels in milk replacers on the disruption of intestinal motility patterns in calves sensitive to soya. J. Vet. Med. Ser. A 42:467–478. 15 Le Dre´an, G., I. Le Hue¨rou-Luron, J. A. Chayvialle, V. PhilouzeRome´, M. Gestin, C. Bernard, R. Toullec, and P. Guilloteau. 1997. Kinetics of pancreatic exocrine secretion and plasma gut regulatory peptide release in response to feeding in preruminant and ruminant calves. Comp. Biochem. Physiol. Ser. A 117:245–255. 16 Le Dre´an, G., I. Le Hue¨rou-Luron, M. Gestin, D. Fourmy, and P. Guilloteau. 1997. Effects of CCK and gastrin on pancreatic secretion in vivo in the calf. Reprod. Nutr. Dev. 37:354–355. 17 Le Dre´an, G., I. Le Hue¨rou-Luron, V. Philouze-Rome´, R. Toullec, and P. Guilloteau. 1995. Response of the calf pancreas to differently processed soybean and pea diets. Ann. Nutr. Metab. 39:164–176. 18 Leiter, A. B., W. Y. Chey, and A. S. Kopin. 1994. Secretin. Pages 147–173 in Gut Peptides. J. H. Walsh and G. J. Dockray, ed. Raven Press, New York, NY. 19 Le Meuth, V., V. Philouze-Rome´, I. Le Hue¨rou-Luron, M. Formal, N. Vaysse, C. Gespach, P. Guilloteau, and D. Fourmy. 1993. Differential expression of A-subtype and B-subtype of cholecystokinin gastrin receptors in the developing calf pancreas. Endocrinology 133:1182–1191. 20 Lewis, L. D., and J. A. Williams. 1990. Regulation of cholecystokinin secretion by food, hormones, and neural pathways in the rat. Am. J. Physiol. 258:G512–G518. 21 Liu, K., and P. Markakis. 1989. An improved colorimetric method for determining antitryptic activity in soybean products. Cereal Chem. 66:415–422. 22 Lowry, O. H., N. J. Rosebrough, A. L. Farr, and R. J. Randall. 1951. Protein measurement with the folin phenol reagent. J. Biol. Chem. 193:265–275. 23 Maner, J. H., W. G. Pond, J. K. Loosli, and R. S. Lowrey. 1962. Effect of isolated soybean protein and casein on the gastric pH

SOYBEAN PROTEIN AND PANCREATIC SECRETION and the rate of passage of food residues in baby pigs. J. Anim. Sci. 21:49–51. 24 Pierzynowski, S. G., R. Zabielski, P. Podgurniak, P. Kiela, P. Sharma, B. Westro¨m, S. Kato, and J. W. Barej. 1992. Effects of reversible cold vagal blockade and atropinization on exocrine pancreatic function during liquid food consumption in calves. J. Anim. Physiol. Anim. Nutr. 67:268–273. 25 Pierzynowski, S. G., R. Zabielski, B. R. Westro ¨ m, M. Mikolajczyk, and J. W. Barej. 1991. Development of the exocrine pancreatic function in chronically cannulated calves from the preweaning period up to early rumination. J. Anim. Physiol. Anim. Nutr. 65:165–172. 26 SAS/STAT® User’s Guide: Statistics, Version 6, 4th Edition. 1990. SAS Inst., Inc., Cary, NC. 27 Singer, M. V. 1987. Pancreatic secretory response to intestinal stimulants: a review. Scand. J. Gastroenterol. 22(Suppl. 139): 1–13. 28 Ternouth, J. H., J.H.B. Roy, S. Y. Thompson, J. Toothill, C. M. Gillies, and J. D. Edwards-Webb. 1975. Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion of calves. Br. J. Nutr. 33:181–196. 29 Tolman, G. H., and G. M. Beelen. 1996. Endogenous nitrogen and amino acid flow in the terminal ileum of veal calves and true digestibility of skim milk, soluble wheat and soya isolate

1321

proteins. Pages 191–207 in Veal Perspectives to the Year 2000. Fe´de´ration de la Vitellerie Franc¸aise, Paris, France. 30 Toullec, R., and P. Guilloteau. 1989. Research into the digestive physiology of the milk-fed calf. Pages 37–55 in Nutrition and Digestive Physiology of Monogastric Farm Animals. E. J. Van Weerden and J. Huisman, ed. Pudoc, Wageningen, The Netherlands. 31 Toullec, R., J. P. Lalle`s, and P. Bouchez. 1994. Replacement of skim milk with soya bean protein concentrates and whey in milk replacers for veal calves. Anim. Feed Sci. Technol. 50: 101–112. 32 Tukur, H. M., J. P. Lalle`s, C. Mathis, I. Caugant, and R. Toullec. 1993. Digestion of soybean globulins, glycinin, aconglycinin and b-conglycinin in the preruminant and the ruminant calf. Can. J. Anim. Sci. 73:891–905. 33 Walsh, J. H., and G. J. Dockray. 1994. Gut Peptides: Biochemistry and Physiology. Raven Press, New York, NY. 34 Zabielski, R., T. Onaga, H. Mineo, S. G. Pierzynowski, and S. Kato. 1994. Local versus peripheral blood administration of cholecystokinin-8 and secretin on pancreatic secretion in calves. Exp. Physiol. 79:301–311. 35 Zabielski, R., Y. Terui, T. Onaga, H. Mineo, and S. Kato. 1994. Plasma secretin fluctuates in phase with periodic pancreatic secretion and the duodenal migrating myoelectric complex in calves. Res. Vet. Sci. 56:332–337.

Journal of Dairy Science Vol. 81, No. 5, 1998