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2
,§,§,
*
Institute of Animal Nutrition (450), Hohenheim University, D-70593 Stuttgart, Germany;
Orffa Germany GmbH, D-46483 Wesel, Germany;
**
The Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences, 05–110 Jablonna, Poland;
Department of Cell and Molecular Biology, Lund University, S-223 62 Lund, Sweden;
Department of Animal Physiology, Lund University, S-223 62 Lund, Sweden;
Gramineer Int. AB, Ideon beta, S-223 62 Lund, Sweden; and
§
Institute of Biochemistry and Biophysics, Polish Academy of Sciences, 02-106 Warsaw, Poland
2To whom correspondence should be addressed.
 |
ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: • pigs • pancreatic secretion • fat • cholecystokinin • peptide YY
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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).
Enzyme secretion is highly dependent on diet composition, age and
feeding regimen (Corring et al. 1989
). This has been
well described for different species including rats (Bucko and Kopec 1968
, Gidez 1973
), dogs (Behrmann and Kare 1969
) and pigs (Corring 1980
,
Makkink and Verstegen 1990
, Ozimek et al. 1995
). For example, Mourot and Corring (1979)
observed higher lipase contents in porcine pancreatic tissue with
increasing levels of fat in the diet. Deschodt Lanckman et al. (1971)
and Ricketts and Brannon (1994)
showed
increased lipase contents in rats when polyunsaturated fatty acids
(PUFA)3
were included in the diet. Simoes Nunes (1986)
fed diets
to pigs containing either 21 g/100 g sunflower oil or lard and showed
that sunflower oil evoked a higher (P < 0.05) lipase content than
lard. In studies by Gabert et al. (1996)
, pigs were
prepared with a pancreatic duct catheter and adapted to diets
containing either coconut oil, rapeseed oil or fish oil. The authors
found a higher (P < 0.05) chymotrypsin secretion in pancreatic
juice of pigs fed a diet supplemented with coconut oil, and higher (P
< 0.05) secretion of carboxylester hydrolase in pigs fed a diet
containing fish oil. The gastrointestinal hormones
Peptide YY (PYY) and cholecystokinin (CCK) are considered to be
major regulative hormones of the exocrine pancreas. Several authors
showed that fat stimulated the release of PYY in dogs (Aponte et al. 1985
, Lluis et al. 1989
, Pappas et al. 1985
) and the release of CCK in dogs (Shiratori et al. 1989
) and cats (Backus et al. 1995
) as well.
The effect of dietary fat on plasma CCK levels in pigs is discussed
equivocally because Corring and Chayvialle (1987)
could
not observe any effect, whereas Cuber et al. (1990)
reported a stimulatory effect of fats. Moreover, Yago et al. (1997a)
demonstrated in humans that not only the quantity of
fat consumed but also the composition of dietary fat influenced plasma
CCK and PYY levels. A diet based on olive oil with a higher degree of
saturation than sunflower oil evoked higher hormone levels compared
with the diet supplemented with sunflower oil.
In most studies, dietary changes elicited a fast response in enzyme
adaptation and the secretion of gastrointestinal hormones, which took
place completed within 1 wk (Bucko and Kopec 1968
,
Corring 1980
, Deschodt Lanckman et al. 1971
). There is evidence for the existence of such a mechanism
in rats (Bucko and Kopec 1968
, Deschodt Lanckman et al. 1971
), pigs (Corring and Chayvialle 1987
,
Hee et al. 1988
) and dogs (Yago et al. 1997b
).
However, there is still a scarcity of information on the existence of a spontaneous adaptation of the exocrine pancreas when fully saturated fatty acids different in chain length are fed to pigs. The objectives of this study were to examine the effect of purified fat sources, namely, glycerol tricaprylate (8:0) and glycerol tristearate (18:0), on the spontaneous exocrine pancreatic secretion in pigs and on plasma levels of the gastrointestinal hormones CCK and PYY.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The studies were carried out with six piglets [Swedish Landrace x (Yorkshire x Hampshire)] obtained from a production herd (Odarslöv’s Research Farm, Swedish University of Agricultural Sciences, Lund) with an average body weight of 13.6 kg at the beginning of the experiment. The pigs were housed individually; they had free movement in pens (1 x 2 m), free access to water and were kept under a 12-h light:dark cycle (light from 0800 to 2000h). Treatments and experiments were conducted according to the European Community regulations concerning the protection of experimental animals and Lunds University Ethical Committee Allowance.
Surgical procedures.
The pigs were sedated with azaperone (Stresnil, Janssen Pharmaceutica,
Beerse, Belgium; 2 mg/kg body) and anesthetized with Halothane (ISC
Chemicals, Tarrytown, NY; 3% air). Surgery was performed under
aseptic conditions. The pigs were surgically fitted with a chronic
pancreatic duct catheter and a T-shaped duodenal cannula for
collection and subsequent return of pancreatic juice into the duodenum
according to Pierzynowski et al. (1988)
and modified as
described by Thaela et al. (1995)
. This method allows
for the quantitative sampling of 100% pure, nonactivated pancreatic
juice and therefore for a quantitative measurement of the volume of
secretion of pancreatic juice. Additionally, a catheter for blood
sampling was implanted into the vena jugularis according to
Pierzynowski et al. (1988)
.
Experimental procedures.
The piglets were fed twice daily (1000 and 1600 h) a
barley-based starter diet with 17.7% crude protein and 5.2% crude
fat (Växfor, Lantmännen, Stockholm, Sweden) at a rate of 2
g/100 g body. After a postsurgical recuperation period of 7 d,
beginning with the morning feeding (1000 h), a medium-chain
triglyceride (MCT: glycerol tricaprylate, Fluka, Deisenhofen, Germany)
or a long-chain triglyceride (LCT: glycerol tristearate, Fluka) or
saline as a control was infused directly into the duodenum of the
piglets via the duodenal T-cannula. The daily amount of fat infused
into the duodenum amounted to 0.1 g/100 g body, which corresponds to
5% fat supplementation to the diet. Syringes were filled with the fats
and saline was added to a final volume of 36 mL. They were kept under
heating lamps at body temperature and were emulsified by means of
vigorous shaking just before the infusions started. The fat treatments
and the control infusion with saline (36 mL) were administered in small
boluses of 3 mL per bolus every 5 min over a period of 1 h (1000
to 1100 h). The fats were provided according to a 3 x 2
Latin square design; the fatty acid composition of the fats infused is
shown in Table 1
.
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Additionally, blood samples of 5 mL were obtained 15 min preprandially and 15, 45, 90 and 150 min postprandially. The samples were taken with syringes containing 4 mmol EDTA and 1000 KIU (Kallikrein Inhibitor Unit) Trasylol (Bayer, Leverkusen, Germany) as a proteinase-inhibitor. The blood samples were immediately ice-chilled and centrifuged at 3434 x g. The plasma obtained was stored at -20°C until analyses.
Analytical procedures.
The fats infused were analyzed for their fatty acid composition by
means of a gas liquid chromatography procedure according to
Naumann et al. (1976)
. Pancreatic juice samples were
analyzed for protein using the Lowry method (Lowry et al. 1951
), performed on 96-well microwell plates, with bovine serum
albumin (Sigma, St. Louis, MO) as a standard. Intra- and interassay CV
for the protein determination were 3.1 and 3.6%, respectively. Trypsin
(EC 3.4.21.4) activities were estimated after enterokinase (Sigma)
activation using
N-
-benzoyl-DL-arginine-p-nitroanilide
(Sigma) as a substrate (Pierzynowski et al. 1990
).
Intra- and interassay CV for the trypsin determination were 2.8 and
3.2%, respectively. Lipase (EC 3.1.1.3) activities were determined by
a pH-stat titration method using tributyrin as a substrate, as
described by Borgström and Hildebrand (1975)
.
Interassay CV for the lipase activity was 4.2%. One unit (U) of enzyme
activity is defined as the amount of enzyme hydrolyzing 1 µmol
substrate per minute. A competitive ELISA was used for measuring
pancreatic colipase. The estimation was adapted to a procedure
described for measuring enterostatin (Mei et al. 1993
).
Antiserum was obtained by immunizing a rabbit (3BI-16) with porcine
procolipase [purified from porcine pancreas according to the method of
Erlanson et al. (1973)
]. Microtiter plates (96-well)
were coated overnight with 0.2 mg/L purified procolipase
(Erlanson et al. 1973
). The antibody against procolipase
was diluted 1:5000, the secondary biotin conjugated antibody (Sigma)
was diluted 1:6000 and the streptavidin-alkaline phosphatase
(Sigma) was diluted 1:6000. The plate was developed by the addition of
p-nitrophenyl phosphate (Sigma), and a standard curve
(r2 = 0.99) ranging from 500 mg/L to
0.7 mg/L was used in this assay [50% inhibitory dose
(ID50) = 34 mg/L]. A RIA kit was used for the
determination of plasma CCK levels (Eurodiagnostica, Malmö,
Sweden; crossreactivity with gastrin sulfated < 0.5%, with
gastrin nonsulfated < 0.01%; assay C-terminally oriented)
and for plasma PYY levels (Peninsula, St. Helens, UK; crossreactivity
with pancreatic polypeptide < 0.01%; assay C-terminally
oriented). The methods recommended by the manufacturers were used
except for minor modifications for the PYY estimation, i.e., before
extracting the peptides out of the sample solutions, the recommended
Sep-Pak C18 (Sep-Pak Vac 3cc, Waters, Milford, MA)
cartridges were pretreated with 100% acetonitrile (Merck, Darmstadt,
Germany). After the columns were conditioned, they were loaded with 2
mL sample solution. Intra-assay CV and recovery were 16 and 80%
for CCK and 14 and 67% for PYY, respectively.
Protein contents in pancreatic juice were expressed as g/L; protein outputs were expressed as mg/(h · kg). Enzyme contents in pancreatic juice were expressed as kU/L; enzyme outputs were expressed as U/(h · kg body). Colipase contents in pancreatic juice were expressed as µg/L, and colipase outputs were expressed as µg/(h · kg body). Plasma CCK levels were expressed as pmol/L, and plasma PYY levels were expressed as ng/L.
Statistical analyses.
Data were analyzed with StatView software (version 4.57, Abacus Concepts, Berkeley, CA) using repeated-measures ANOVA with time, treatment and time x treatment interaction in the model. Scheffé’s post-test was performed to compare treatment means of the pooled data. The results were expressed as means ± SEM The level of significant difference was set at 5% (P < 0.05).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The infusion of MCT evoked a postprandial decrease in the volume of
secretion from 2.6 mL/(h · kg) (30 min postprandially) to a value of
0.25 mL/(h · kg) (2 h postprandially) (Fig. 1
). There was a minor increase 4 h postprandially, which amounted to
1.3 mL/(h · kg). As a result, for the volume of secretion, the trend
of the curve for the MCT treatment changed (P < 0.01), whereas no
changes (P > 0.2) for the LCT and saline infusions were obtained.
A difference (P < 0.02) between the diurnal patterns of the
curves for the MCT and saline treatment was observed, whereas the
curves for MCT and LCT treatment tended to (P < 0.10) different
trends of the curves. No difference (P > 0.3) between the trends
of the curves for saline and LCT infusions was obtained.
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The diurnal patterns of trypsin contents did not change (P > 0.1) for the saline and MCT infusions, whereas the LCT infusions evoked a change in the trend of the curve (P < 0.01). However, no differences (P > 0.05) between the trends of the curves were observed. A prandial increase in the outputs of trypsin was obtained for all three treatments. However, the trend of the curve for the MCT treatment decreased to below preprandial values [from 3.78 to 0.99 U/(h · kg)] 90 min postrandially and recovered to preprandial values 4 h postprandially. The diurnal patterns of the MCT (P < 0.01) and LCT (P < 0.03) infusions changed, whereas the control infusion with saline had no effect (P > 0.4) on trypsin output. Moreover, the trends of the curves for the trypsin outputs differed between LCT and MCT treatments as well as between the saline and the MCT treatments (P < 0.01). No difference (P > 0.2) between the diurnal patterns of the saline and LCT infusion was obtained.
Lipase contents showed a nondirectional trend of the curves for saline
and MCT infusions (P > 0.2), whereas the LCT infusions evoked a
change (P < 0.05) of the trend of the curve; a prandial peak
(2.5-fold increase compared with preprandial value) 30 min
postprandially was observed (Fig. 2A
). The diurnal patterns of LCT and MCT infusions differed (P < 0.02) from each other, whereas no difference (P > 0.1) was found
between the saline and LCT or between the saline and MCT treatment. The
trend of the curve for lipase outputs did not change (P > 0.4)
for the saline treatment, whereas there was a tendency toward a change
(P < 0.06) in the trend of the curve for the MCT treatment and a
significant (P < 0.01) change in the diurnal pattern of the LCT
infusion (Fig. 2B
). Lipase outputs increased twofold and
1.6-fold for the LCT and MCT treatments, respectively, 30 min
postprandially compared with preprandial values. Although lipase
outputs decreased to below preprandial values for the MCT infusion,
lipase outputs for the LCT treatment remained high, ranging from 1.5-
to 2-fold over preprandial values. The trends of the curves between MCT
and LCT treatments were different (P < 0.03), whereas no
difference between saline and MCT (P > 0.2) or between saline and
LCT treatments (P > 0.3) was observed.
|
). A postprandial increase of the colipase content was observed for both
the MCT and LCT treatments, peaking 1 h postprandially at 56.3 and
58.7 mg/L, respectively. No differences (P < 0.2) between the
trends of the curves were obtained. The diurnal patterns of the
colipase output changed with respect to time (P < 0.01) for the
MCT infusion, whereas the infusion of saline and LCT had no effect (P
> 0.1). Colipase output increased fourfold after infusion of LCT
compared with preprandial values and remained at this elevated level
for 2.5 h. The trends of the curves differed (P < 0.01)
between the saline and MCT treatment as well as between the MCT and LCT
treatment, whereas no difference (P > 0.7) between saline and LCT
infusions was found (Fig. 3B
).
|
). Although the curves do not differ (P > 0.2) from each other,
the comparison of treatment means of the pooled data showed that the
MCT treatment resulted in 35 and 40% lower (P < 0.01) plasma CCK
levels compared with the saline and LCT treatment, respectively.
|
25 ng/L (Fig. 5
).
|
|
DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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and Thaela et al. (1995)
. Protein and
trypsin outputs showed very similar diurnal patterns, which might be
related to the fact that in the pancreatic juice of pigs, the ratio
between trypsin and protein is fourfold higher than the values obtained
in the pancreatic juice of rats. This suggests that trypsin is a major
component of the protein fraction in the pancreatic juice of pigs
(Harada et al. 1982
). Pancreatic lipase is most
important for fat digestion in the small intestine. However, on the
basis of the lipase contents in pancreatic juice, the results for the
different infusion treatments are equivocal and no clear evidence
exists for the influence of fats differing in chain length on
pancreatic lipase secretion. On the basis of lipase outputs,
representing the lipase content in relation to its corresponding value
in volume of secretion, however, three different trends of the curves
for the three different infusion treatments were obtained. Lipase
outputs did not change in the diurnal pattern after saline infusion,
whereas the MCT treatment evoked a prandial peak and a postprandial
decrease to below preprandial values. On the other hand, after LCT
infusions, the lipase outputs remained at the prandial elevated level.
Moreover, this pattern for each of the infusion treatments is also
similar for colipase contents and outputs.
The different infusion treatments had only minor effects on plasma PYY
levels, which confirms observations by Aponte et al. (1985)
who showed that infusion of either lauric (12:0) or
oleic (18:1) acid into the proximal duodenum did not evoke a PYY
release. In contrast, ileal and combined duodenal and ileal infusions
of lauric or oleic acid produced similar significant increases in
plasma PYY levels. The authors concluded that plasma PYY levels are not
influenced by the chain length of fatty acids. It cannot be excluded
that in the present study, the absolute amounts of triglycerides
infused intraduodenally were not sufficient to stimulate the PYY
release at the ileal level. Moreover, Serrano et al. (1997)
pointed out that the degree of saturation of fatty acid
must be considered as an important stimulus for PYY release. In humans,
the consumption of a diet containing olive oil with high levels of
monounsaturated fatty acids evoked higher plasma PYY levels than the
consumption of a diet containing sunflower oil with high levels of PUFA
(Serrano et al. 1997
). This may explain why no
differences in plasma PYY levels were observed in this study because
the fats infused were both fully saturated.
The plasma CCK levels for the saline and LCT treatments did not differ
from each other, which confirms observations in pigs (Corring and Chayvialle 1987
). These authors did not find a difference
in plasma CCK levels after consumption of either a high fat or high
starch diet compared with a balanced control diet. However, in the
present study, the plasma CCK concentrations decreased after the start
of the MCT infusions. This decrease follows the same diurnal pattern as
was obtained for enzyme outputs during the experimental periods. CCK is
a potent stimulus for pancreatic secretion in pigs (Houe et al. 1997
, Pierzynowski et al. 1995
), and different
CCK-mediated feedback mechanisms, as described recently by
Pierzynowski et al. (1999)
, are responsible for the
close relationship between enzyme secretion and plasma CCK levels.
In addition, there are indications that the CCK release might be
influenced by plasma PYY levels. Fifteen minutes after the infusion of
MCT, the plasma PYY showed a great variation (mean 36.7 ng/L,
SEM 16.0) which suggests that at least in some pigs, PYY
release was highly stimulated. Coincidentally, the plasma CCK level
started to decrease 90 min after the beginning of the MCT infusions. A
possible explanation for this interaction is provided by Lluis et al. (1988)
who showed in adult dogs that a suppression of
CCK release was linked to an increase in plasma PYY levels. They
concluded that the CCK release was inhibited by an increased PYY
release.
The reason for the decrease in volume of secretion after MCT infusions,
resulting in similar decreases in enzyme outputs, remains unclear. One
possible explanation was provided by Layer et al. (1990)
who could show in humans that small quantities of nutrients (e.g., fat)
that were perfused into the ileum decreased pancreatic enzyme secretion
by >80% (P < 0.001) compared with perfusions with saline.
Moreover, Furuse et al. (1992)
demonstrated that MCT are
absorbed via the blood and the lymphatic system, whereas LCT are
absorbed exclusively via the lymphatic system. This difference could
mediate different hormonal feedback mechanisms. Furthermore, MCT might
be absorbed at a higher rate than LCT, resulting in lower quantities
reaching the ileum of pigs.
In conclusion, the infusions of different fats into the duodenum under
prandial conditions evoked different responses. It can be assumed that
the chain length of the fats infused will have an influence on the
release of CCK and therefore on exocrine pancreatic secretions. There
is no clear evidence that PYY is mediating the regulation of exocrine
pancreatic secretions with respect to fat digestion. Furthermore, the
results of this study clearly show that enzyme and protein contents do
not reflect physiologic conditions; therefore, studies based on the
slaughter method must be reviewed critically. This method does not
allow for the measurement of enzyme outputs because long-term
collections of pancreatic juice are not possible. According to
Sauer and Mosenthin (1999)
, only results expressed in
outputs rather than contents are a true reflection of the effect of
dietary treatments on the exocrine pancreas because differences in
contents may simply reflect dilution by pancreatic juice.
Further investigations are warranted to identify the factors that may be responsible for the changes in the volume of secretion, enzyme secretion and the release of gastrointestinal hormones after MCT infusions. Further studies should focus on gastrointestinal hormones involved in the regulation of the exocrine pancreas, such as CCK and PYY, but also neurotensin and secretin. The determination of the diurnal pattern of secretin in plasma is of particular interest because secretin is considered to be the major regulative hormone of the volume of pancreatic secretion.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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3 Abbreviations used: CCK, cholecystokinin; LCT, long-chain triglyceride; MCT, medium-chain triglyceride; PUFA, polyunsaturated fatty acids; PYY, peptide YY.
Manuscript received January 13, 2000. Initial review completed March 20, 2000. Revision accepted July 4, 2000.
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