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Submitted on 1 Jan 1977
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EFFECTS OF DIET ON THE MOTILITY OF THE
SMALL INTESTINE AND PLASMA INSULIN
LEVELS IN SHEEP
Lionel Bueno, T.E.C. Weekes, Y. Ruckebusch
To cite this version:
EFFECTS
OF
DIET
ON THE
MOTILITY
OF THE
SMALL
INTESTINE
AND PLASMA INSULIN LEVELS IN SHEEP
L.
BUENO
T.E.C. WEEKES
Y. RUCKEBUSCH*
*
Laboratoire de Physiologie-Pharmacadynamie, Ecole Nationale Vétérinaire,
31076 Toulouse Cedex, France
*
&dquo; Rowett Research
lnstitute,
Bucksburn, Aberdeen AB2 9SB, ScotiandRésumé
INFLUENCE DE L’ALIMENTATION SUR LA MOTRICITE INTESTINALE ET L’INSULINEMIE CHEZ LE MOUTON. - L’influence de la nature des aliments sur la motricité
iéjuno-iléale
a
été
envisagée
surcinq
moutons en stabulation recevant au cours depériodes
successives de 21jours :
foin, herbe ou concentrés à base de céréales offerts ad lib. 8 h parjour.
L’activité
électrique
de l’intestingrêle
a étéenregistrée
de façon continuependant
toute la durée des essais àpartir
d’électrodesimplantées
chroniquement.
La teneurplasmatique
englucose
et insuline a été évaluée àpartir
deprélèvements sanguins
effectués avant etpendant
lespériodes
d’essai.Le nombre de
complexes myoélectriques
(14
± 3/24h)
n’est pas modifiésignificativement
(P 5
0,05)
par la nature de l’aliment ;cependant,
la durée totale d’activitérapide
estsupérieure
(13
et 18%) lorsque
l’animal reçoit de l’herbe et des concentrés au lieu de foinlong.
La durée de l’activitérapide
de lapériode
d’accès aux aliments est accrue dans le cas desconcentrés ;
l’insulinémie, qui
n’est pas modifiée parl’ingestion
de foin oud’herbe,
est, pourles concentrés,
augmentée
de 36,8 °!.En
définitive, quel
que soit lerégime
alimentaire,
lescomplexes
myoélectriques
(MMC)
migrant
lelong
de l’intestin sont permanents chez le mouton. Une alimentation riche en éléments directement assimilables parl’organisme
dans le cas où elle est distribuée sous la forme d’un seul repasjournalier
estcapable
dedésorganiser
de façon transitoire leprofil
moteur de l’intestingrêle.
Cephénomène s’accompagne
d’unehyperinsulinémie
ana-logue
à celle observée chez lesmonogastriques.
Introduction
In adult
sheep
amajor
pattern of electrical activity of the small intestine is themigrating
myoelectric complex (MMC) (Grivel
andRuckebusch,
1972).
This comprises aphase
of
irregular spiking activity (ISA)
followedby
a briefperiod
ofregular spiking
(RSA)
which in turn is followed
by
aperiod
ofquiescence
during
whichonly
slow waves aredetected
(Ruckebusch
and Bueno,1975). The
complexes
arepropagated along
the intestineand recur at intervals of about 85 min
(Bueno,
the MMC
pattern
occursduring fasting,
but it isdisrupted
by feeding ;
during feeding
and for up to 8 hafterwards
irregular
spiking
is continuous
(Code
and Marlett,1975)
andis associated with an increased flow of
digesta
(Bueno
et al.,1975).
The MMCpattern
is notdisrupted by
a meal ofhay
insheep (Grivel
andRuckebusch,
1972)
orruminant calves
(Ruckebusch
and Bueno,1973).
Recently,
Bueno and Ruckebusch(1976)
have shown that
injections
of insulin orinsulin
secretagogues
into fasteddogs
resultin a pattern of electrical
activity
similar tothat seen after
feeding.
Continuousirregular
spiking
is also elicited insheep by
ahigher
dose of insulin or
by
an intravenous infusionof volatile
fatty
acids into normal, but not into alloxan-induced diabeticsheep (Bueno
and Ruckebusch,
1976).
Although
apost-prandial
elevation inplasma
immunoreactive insulin(IRI)
levels has been described inadult ruminants
(see
Bassett,1975),
thechanges
are most consistent when cerealsare fed
(Lofgreen
and Warner, 1972 ;Jenny
and
Polan, 1975).
Thepresent study
there-foreinvestigated
therelationship
betweenplasma
insulin and the MMC insheep
fed oneither fresh cut grass,
hay,
or cerealpellets.
Materials and methods
Animal and
surgical preparation
Five adult
Lacaune ewesweighing
35 to50
kg
were used. All animals had beenkept
at pasture and were
thoroughly
accustomedto
handling.
Underthiopental
sodium(20
mg/
kg)
anaesthesia a 10 cmlong laparotomy
performed
on theright
sideabout
4 cmposterior
to thelast
rib allowed access tothe
proximal jejunum.
Electrodes made ofinsulated stainless-steel wires 120 pm in diameter and 1.5 m in
length (Grivel
and Ruckebusch,1972)
wereimplanted
on thesmall intestine
(Ruckebusch,
1970)
in groupsof
three,
2 mm apart.Groups
wereimplanted
at 1 m intervals from 3 to 7 m from the ileo-caecal
junction.
The free ends of the elec-trodes were exteriorized on theright
side.Animals
were alsoequipped
at surgery withan
indwelling jugular
catheter.Diets
Four animals received each of the
following
diets for successiveperiods
of 20-22days :
1)
fresh grass, cutdaily,
of mediumquality,
2) long hay
ofpoor
quality,
3)
cerealpellets (12.5 mm)
comprising
(g/kg
freshweight) ground
maize 400,sharps
240, rolled
barley
184,ground
lucerne 90, molasses50,
urea 16, mineralsand
vitamins20
(Magda pellets :
Les Fils d’Henri Vialars,Toulouse)
together
with 0.1kg/day
long hay.
The chemical
composition
of the diets isgiven
in Table 1.One animal failed to consume the cereal
pellets
and the electricalrecordings
fromanother ewe were
disrupted
by
agastro-intestinal nematode infestation. Thus results
were
only obtained
from three of theoriginal
ewes for the
hay
diet and two for the cerealpellets.
An additional animaltherefore
re-ceived
only
the cereal ration.Experimental procedure
Sheep
were housed in metabolism cagesand fed ad libitum at 09.00 hours
(Zero
time)
each
day.
Uneaten food was removed at 17.00. Fresh water was available at all times.Following
the recovery from surgery andadaptation
to the fresh grass diet(5-7
days),
the electrodes werepermanently
connectedto an e.e.g.
machine
(Reega
VIII, Alvar, 93107Montreuil, RC
coupling,
time constant 0.3sec).
Electricalactivity
from each site wasdirectly
recorded for several consecutivehours on 2 or 3
days
each week. Summationof the electrical
activity
from two groups of electrodes for eachsubject
wascontinuously
plotted
at 20 sec intervalsthroughout
theexperiment, using
a double linearintegrator
circuit
(Latour, 1973)
connected to apoten-tiometric recorder
(PM
8010,Philips.
93002Bobigny).
Thisprocedure
allowed andietary
period
wereseparated
intoperiods
of ISA,
RSA
andquiescence.
Results werediscarded when an accurate
separation
ofMMC components was not
possible
through-out a24
hperiod (09.00-09.00 hours).
During
the final week of eachdietary
period jugular
bloodsamples
were taken ontwo non-consecutive
days
at 30 min intervals from 1 h beforefeeding
until 9 h afterfee-ding,
with additionalsamples
10 and 11 hafter
feeding
commenced.Samples
(6 ml)
were
placed
in tubescontaining heparin.
Plasma was removed
by
centrifugation
at 4° and stored at -20° untilanalysed.
Analytical
Plasma
glucose
concentrations wereme-sured
using
a TechniconAuto-Analyser
(Technicon
InstrumentsCorp.,
Tarrytown,
NewYork)
and a modification of the method describedby
Hoffmann(1937).
Plasma IRIlevels were estimated
by
a modification of the method of Bassett and Thorburn(1971),
using
human insulin(24.6
i.u./mg ;
Radio-chemical Centre, Amersham)
as standardand
guinea pig
anti-bovine insulin serum(Lot
GP3; Miles
Research Products,Slough)
at a final dilution of 1:80.00. Antiserum and
samples
or standards were incubated at roomtemperature
for 4 hbefore
addition of 180 pg’ 25
1-labelled insulin
(C.E.A&dquo;
91190 Gif surYvette).
After further incubation for 20 h, free andantibody-bound
hormone were se-parateusing
talc(Bassett
andThorburn,
1971).
).
Calculations
Plasma IRI concentrations were converted
to
logarithms
before calculation of meansand statistical
computations (Bassett
and Thorburn,1971).
Results
Electrical
spiking
activityThe ewes consumed
significantly
lessdry
matter when
fresh
cut grass wasgiven
than with the other two diets. The overall MMCfrequency
was, however, unaffectedby
diet(Table
2)
and was not correlated withdry
matter intake for any diet. The duration of the individual components of the MMC, ISA and RSA, were also unaffected
by
diet
whenvalues were
averaged
over 24 h(Table 2).
The MMC recurred at intervals of 80-120 min
during
thepre-feeding period (-8-0 h)
andmigrated along
the ileum at a mean rate of178 ± 57 mm/min
(n
=80), regardless
ofdiet.
Eating
continuedintermittently
throughout
the
period
of access to food,although
itfresh grass or
hay
weregiven, feeding
hadno effect on the
MMC pattern (Fig. 1)
or theduration
of electricalspiking
activity during
the
8 hfeeding period (Table 3). When
cerealpellets
weregiven,
electricalspiking activity
was
significantly
increasedduring
thefee-ding period compared
to thepre
-
feeding
andpost-feeding
periods (Table 3).
Thischange
resulted from both shorter MMCcycles, particularly
early
in thefeeding
period,
andlonger
periods
of ISA(Fig. 1).
The duration of
spiking activity during
thefeeding
period
was similar for all diets,but
in the
pre-feeding period
lessactivity
was recorded when cerealpellets
weregiven
thanwith grass
(P
<0.01)
orhay (P
<0.001).
Spiking
activity
was also less in thepost-feeding
period
when thesheep
received cerealpellets
compared
tohay (P
<0.05).
Spiking
activity
during
thefeeding period
was not correlated with
dry
matter intake forany diet.
Plasma
glucose
concentrationPlasma glucose
concentration beforefee-ding
was similar for all diets(Fig. 2).
When food was offeredplasma
glucose
concentra-tions tended to rise ; levels weresignificantly
higher
than the meanpre-feeding
value at0.5, 1.0 and 1:5 h when
hay
wasgiven
and at0.5 and 1.0 h when fresh grass was
supplied
(P <
0.05 in allcases).
Plasma insulin concentration
The
pre-feeding
plasma
IRI concentrationconcentrations
displayed
considerablevaria-bility
during feeding (Fig. 2),
but differences from the meanpre-feeding level
were notsignificant
when the ewes received fresh grass orhay
(Fig.
2).
When cerealpellets
were
given,
IRI concentrations werehigher
at 2.5, 3.0, 4.0, 4.5, 5.0 and 5.5 h than before
feeding
(P
< 0.05 in allcases)
and the meanIRI concentration was also elevated
during
feeding (Table 4).
The net insulin responseto
feeding
wassignificantly
greater
when thesheep
received cerealpellets
than forhay
(Table
4).
Plasma IRI concentrationsduring
thefeeding
period (IRI,
p.U/ml)
wereposi-tively
correlated(P
<0.001)
withplasma
glucose
concentrations(PG,
mmol/I)
when cerealpellets
weregiven.
Therelationship,
based oneighty
observations, was :log
lo
IRI = 0.902 ± 0.156 PG
(SE
ofregression
coefficient
0.033,
residual SD0.207, R
2
0.225).
There was no
relationship
between IRI and PG when grass orhay
was fed.When
hay
wasgiven,
the meanplasma
IRIconcentration
(IRI, ¡
L
U/ml)
waslinearly
rela-ted(P
<0.05)
to thedry
matter intake(DMI,
kg/day).
Therelationship,
based on sixobservations, was :
log
io
IRI = 0.974 ± 0.359 DMI(SE
ofregression
coefficient 0.112,resi-dual SD 0.051,
R
2
0.70).
A similar trend was apparent when cerealpellets
weregiven,
but this was notstatistically
significant (0.1
> P >0.05).
The net IRI response to
feeding
on cerealpellets
was not related to either the duration ofspiking
activity
during
thefeeding period
or the difference in the duration of
spiking
between thefeeding
andpre-feeding
periods.
Discussion
The MMC has been termed the
interdiges-tive
myoelectric complex
(Code
andMarlett,
1975),
since in thedog
it isonly
seenduring
fasting.
However, it is clear from our results that the MMCpattern
is notdisrupted
in ruminantsby eating roughage
diets,
inagree-ment with
previous
studiesusing
adultsheep
(Grivel
andRuckebusch, 1972)
and ruminant calves(Ruckebusch
andBueno,
1973).
Even when thesheep
received cerealpellets,
changes
in electricalactivity
wererelatively
small, in
comparison
to the effects of a mealin
dogs (Bueno
et at.,1975 ;
Code andMar-lett,
1975).
The
relatively
poor food intake of the ewesand the
long
period
of access to food mayhave minimised the responses observed. Thus Ruckebusch and Bueno
(1976)
foundthat the intestinal MMC
pattern
wasdisrupted
for 6 h
postprandially
whenpigs
were fedonce
daily,
but it wasscarcely
modified atall when the animals ate ad libitum,
consu-ming
small butfrequent
meals. However,even at the
highest
levels ofdry
matterintake achieved with the
roughage
diets,0.8
kg/day
for grass and 1.2kg/day
forhay,
there was no indication of any diurnal
varia-tion in electrical
activity.
When
compared
to the other diets, intes-tinalspiking
activity
for the cerealpellet
ration was decreasedduring
the pre- andpost-feeding period.
This suggests thatfee-ding
relieved an inhibition ofspiking activity.
Apossible
inhibitory
factor isenteroglucagon,
since a
patient
with a tumourproducing
this materialdisplayed
marked intestinalhypo-motility.
Thepostprandial
release of this hormone occurs later than the release of otherpancreatic
and intestinal hormones in both man andpre-ruminant
calves(Bloom
et
al., 1975).
Thisglucagon-like
immuno-reactive material is veryheterogeneous
(Val-verde,
Dobbs andUnger,
1975)
and it is notknown whether the fraction
affecting
intes-tinal
motility
is present in ruminants,although plasma
levels of total intestinalglucagon-like
immunoreactivity
arehigher
when cattle are fed onbarley
compared
tohay.
The passage of
digesta along
the smallintestine of
sheep
mainly
occurs inassocia-tion with ISA,
particularly immediately
prior
to a
period
of RSA(Bueno
et al.,1975).
The increasedspiking
activity
andchanges
inMMC
frequency. during
thefeeding
period
when the ewes received cereal
pellets
maytherefore indicate an increased flow of
di-gesta,
inagreement
with thefindings
ofThompson
andLamming
(1972).
Theseau-thors
reported
that the flow ofdigesta,
dry
matter and starch to the duodenum of
sheep
was
greatest
4-8 h afterfeeding
adaily
meal ofground pelleted
maize andchopped
orground barley
straw, but diurnal variations inflow were much less when
long
straw wasfed.
The constancy of
plasma
IRI concentra-tions when fresh grass orhay
was fed and thehyperinsulinaemic
response to cerealpellets
are inagreement
withprevious
positively
related to theproportions
of cerealin the ration
(Lofgreen
and Warner, 1972 ;Bhattacharya
and Alulu,1975).
Thedegree
of
hyperinsulinaemia
is howevergenerally
less than that found in
monogastric species
(Mutter
et al., 1970 ; Bueno and Ruckebusch,1976).
Several factors may have contributed to the increased insulin secretion when cereal
pellets
were fed(Bassett, 1975).
Although
thequantities
ofpropionate
andbutyrate
produced
in the rumen wereprobably
grea-test when the
sheep
received cerealpellets
(Bauman,
Davis and Bucholtz, 1971 ; Orskov,Fraser and Gordon,
1974),
these metabolitesare
relatively
unimportant
regulators
ofin-sulin secretion
(Bassett,
1975; Weekes,Bueno and Garcia-Villar,
1976).
A conside-rablequantity
of theground
maize starch in the cerealpellets probably
escaped
ruminaldigestion
(Orskov,
Fraser andKay,
1969).
The relation betweenplasma
concentrationsof
glucose
and IRIduring
thefeeding period
when the
sheep
received cerealpellets
sug-gests that
glucose
maypartially regulate
insulin release insheep
when considerableintestinal starch
digestion
occurs. A strongrelationship
betweenplasma
glucose
and IRIconcentrations was also
reported by Jenny,
Polan andThye (1974)
in bloodsamples
taken 3-4 h afterfeeding
ahigh grain
ration tolactating
dairy
cows. The mean intake ofcrude
protein
when cerealpellets
were fed(0.15
kg/day)
was almost twice that achievedon the other two diets and Bassett, Weston and
Hogan (1971)
found a close relationbet-ween the amount of crude
protein
digested
in the small intestine and insulin levels in
sheep
receiving
avariety
of diets. Thisasso-ciation may have been mediated
by
the release ofgastrointestinal
hormones (Bassett,1975).
Theidentity
of thegastrointestinal
hormone(s)
responsible
for insulin release isuncertain
(see
Grossman,1974),
butgastric
inhibitory polypeptide
appears to be astrong
candidate, at least in man
(Brown
et al.,1975).
High
doses of exogenous insulin orintra-venous infusions of volatile
fatty
acids pro-duce continuousirregular spiking activity
inthe intestine of
sheep (Bueno
andRucke-busch,
1976).
The moderatehyperinsuli-naemia
resulting
fromfeeding
cerealpellets
may therefore have removed the inhibition
of
spiking
activity
and mediated thechanges
in MMC
frequency during feeding.
However,other
postprandial
responses may also havecontributed to the
changes
in electricalspi-king
activity,
since there was noquantitative
relationship
between the effects offeeding
cereal
pellets
onspiking
activity
and the netinsulin response to
feeding.
Sincevagotomy
reduces the duration of ISA in
sheep
(Bueno
and Ruckebusch,
1976),
avagal
reflexme-chanism may be involved, similar to that
producing
arapid
hyperinsulinaemic
responseto
eating
insheep
(Bassett, 1975).
Gastrinrelease has been
suggested
as apartial
me-diator of the
postprandial changes
ofintes-tinal electrical
activity
in thedog
(Weisbrodt
et al.,
1974)
and Bruce and Huber(1973)
reported that
a hormone releasedby
duo-denal modification stimulated intestinalmoti-lity
insheep.
This hormone was notiden-tified, but
cholecystokinin
increases duodenalmotility
in cats(Fara,
Rubinstein andSon-nenschein,
1972).
Thusgastrointestinal
hor-mones may both
participate
in the hyper-insulinaemic response tofeeding sheep
oncereal diets and,
together
with insulin, mayregulate
intestinalmyoelectric activity
when such diets are fed.Summary
1. To determine the effects of diet on intestinal electrical
activity
and insulin secretion, fivesheep
weregiven
diets of fresh cut grass,hay,
and cerealpellets
for successiveperiods
of 20-22days.
Food was available for 8 hdaily.
Continuouselectromyographical
recordings
were made from electrodesplaced
chronically
on thejejuno-ileon.
Plasmaimmunoreactive insulin
(IRI)
andglucose
concentrations were measured before andduring
feeding.
2. The duration of electrical
spiking
activity
was increasedduring
theperiod
ofaccess
tofood when cereal
pellets
were fed, but not when thesheep
received grass orhay.
Thedaily frequency
of themigrating
myoelectric
complex
was unaffectedby
diet.not
change during feeding
when fresh grass orhay
weregiven.
4. It is concluded that
postprandial changes
in intestinal electricalactivity
in thesheep
depend
on the nature of the diet, but are less marked than inmonogastric
species.
Plasma IRI concentrations maypartially regulate
the pattern of electricalactivity.
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