Download Effects of fatty acid chain length and saturation on gastric inhibitory

Bioscience Reports 5, 701-705 (1985)
Printed in Great Britain
701
E I I e c t s of I a t t y acid chain length and saturation
on g a s t r i c inhibitory polypeptide release in o b e s e
hyperglycaemic
(oh/oh) mice
Piotr KWASOWSKI 1, Peter R. FLATT I,
Clifford 3. BAILEY2 and Vincent MARKS 1
IDepartment of Biochemistry, Divisions of Clinical
Biochemistry and Nutrition & Food Science, University of
Surrey, Guildford, U.K.; and 2Department of Molecular
Sciences, Division of Biology, Aston University,
Birmingham, U.K.
(Received 12 August 1985)
Plasma gastric inhibitory polypeptide (GIP) responses to
e q u i m o l a r i n t r a g a s t r i c a l l y administered emulsions of
f a t t y acids (2.62 mmol/7.5 ml/kg) were examined in 18
h fasted obese hyperglycaemic (ob/ob) mice. Propionic
acid (C3:0), a saturated short-chain f a t t y acid, and
capric acid (C10:0), a saturated medium chain f a t t y
acid, did not s i g n i l i c a n t l y s t i m u l a t e GIP release.
H o w e v e r , the saturated long-chain f a t t y acid stearic
acid (C18"0), and especially the unsaturated long-chain
f a t t y acids oleic (C18:1), linoleic (C18:2) and linolenic
(C18:3) acids produced a marked GIP response.
The
results show that chain length and to a lesser extent
the degree of saturation are important determinants of
f a t t y a c i d - s t i m u l a t e d GIP release.
The GIP-release
action of long-chain, but not short-chain, fatty acids
m a y be r e l a t e d to differences in their intracellular
handling.
Gastric inhibitory polypeptide (GIP) is secreted by the K-cells of the
intestinal mucosa during the alimentary processing of food (Brown,
1982; Creutzfeldt, 1982; Marks & Morgan, 1983).
In addition to its
possible role in the control of gastric acid secretion (Brown, 1982),
GIP e x e r t s a g l u c o s e d e p e n d e n t i n s u l i n - r e l e a s i n g e f f e c t on the
pancreatic islet B-cells, and constitutes a physiological component of
the enteroinsular axis (Brown, 1982; Creutzfeldt, 1982; Marks &
Morgan, 1983).
Studies in many species, including man, have shown
that GIP secretion is stimulated by carbohydrates, proteins and fats
(Brown, 1982).
Dietary fats provide an especially potent stimulus for GIP release
(Brown et al., 1975; Falko et al., 1973; O'Dorisio et al., 1976), but
the mechanism is not established. Thus, in contrast to the prominent
effect of triglycerides, variable GIP responses have been observed to
f a t t y acids and mono- and di-glycerides (Ross & Shaffer, 1981;
Williams et al., 19gl).
Recent studies have identified the genetically
702
KWASOWSKI ET AL.
obese hyperglycaemic (ob/ob) mouse as a valuable model to investigate GIP release. This model exhibits intestinal hypertrophy (Flatt et
al., 1983) and enteroendocrine hyperplasia (Polak et al., 1975), with
enhanced basal and nutrient-stimulated GIP concentrations (Flatt et
al., 1983, 198#). The present study investigates the effects of fatty
acid chain length and saturation on GIP release in ob/ob mice.
Materials
and Methods
Groups of Aston obese hyperglycaemic (ob/ob) mice from the
colony maintained at Surrey University were used at 12-18 weeks of
age.
The origin and characteristics of Aston ob/ob mice have been
described elsewhere (Flat & Bailey, 1981; Bailey et al., 1982). Mice
were housed in an air-conditioned room at 22 + 2~ with a lighting
schedule of 12 h light (0700-1900 h) and 12 h darkness. A standard
pellet diet (Spratts Laboratory Diet 1, Lillico Ltd., Reigate, U.K.) and
tap water were supplied ad libitum.
This diet comprised 3.5% fat,
21.5% protein and #g% carbohydrate (digestible energy 1#.2 MJ/kg)
with added fibre, vitamins and minerals.
F a t t y acids (Sigma Chemical Company Ltd., Poole, U.K.) were
administered intragastrically as an aqueous emulsion (2.62 mmol/7.5
ml/kg) to conscious 18 h fasted mice.
The dose corresponded with
the overall composition of the fat emulsion (Intralipid, Kabi Vitrum
L t d . , Ealing, U.K.) previously tested in ob/ob mice (Flair et al.,
1984).
The f a t t y acids (with numbers of carbon atoms: unsaturated
carbon-carbon bonds, and dose in mg/kg) were: propionic acid (C3:0,
19# mg/kg), capric acid (Cl0:0, #51 mg/kg), stearic acid (Clg:0, 7#6
mg/kg), oleic acid (C18:I, 741 mg/kg), linoleic acid (cIg:2, 735
mg/kg) and linolenic acid (cIg:3, 730 mg/kg).
Blood samples (60 lal)
were taken from the tail-tip of conscious mice immediately before and
at 30, 60, 90 and 120 min after fatty acid administration.
Plasma GIP was measured by radioimmunoassay (Morgan et al.,
197g) using donkey anti-rabbit g a m m a globulin antiserum (Guildhay
Antisera, University of Surrey, Guildford, U.K.) for separation of free
from bound antigen. Porcine GIP (Professor 3.C. Brown, University of
British Columbia, Canada) was used to prepare 1251-GIP and as
standard. Immunoadsorbed GIP-free human plasma was added to the
tubes of the standard curve used to minimize non-specific interference,
and parallelism was demonstrated between the standard curve and
serially diluted ob/ob mouse plasma.
The GIP antiserum (RIC 34/11I;
Guildhay Antisera) recognizes both 5000 and g000 molecular forms of
GIP. It exhibits negligible cross reactivity (less than i % ) with other
e n t e r o - p a n c r e a t i c hormones, including cholecystokinin, glucagon, gut
g l u c a g o n - l i k e immunoreactivity (enteroglucagon), insulin, pancreatic
p o l y p e p t i d e , proinsulin C-peptide, secretin and vasoactive intestinal
polypeptide.
Groups of data were compared by analysis of variance
(ANOVA). Differences were considered to be significant if P < 0.05,
and these were confirmed using Student's paired and unpaired t-tests
as appropriate.
Results
Mean basal plasma GIP concentrations in the experimental groups
of 18 h f a s t e d ob/ob mice were 526-614 pg/ml (Fig. 1).
Oral
administration of propionic acid, a saturated short-chain (C3:0) f a t t y
FATTY
ACIDS
I
7000
t
AND
GASTRIC INHIBITORY PEPTIDE
Propionic acid
(C3:0)
a691 + 350
(c18:o)
I
-/+---T
i
;
m-__
kinoleic acid
(C18:2)
A2550 • 691
(c]8:])
A2389 • 382 [
~I
A1348+ 436 ,
+
Oleic acid
3000
Stearic acid
Capric acid
(el0:0)
5216 i 281
oooI , / §-
703
l
I
|
L ~ _ _ ' ,
I
Lino]enic acid
(d8:3)
z~]508 + 665
|
-
t-+
K
I000
0
O/~
--,
J
0
30
I
I
60
90
.~
120
I
I
I
I
0
30
60
90
I
]20
I
0
I
30
I
I
I
60
90
120
--
Minutes
Fig. i.
Effects of fatty acid chain length and
s a t u r a t i o n on plasma GIP concentrations in 18 h
fasted ob/ob mice.
Fatty acids were administered
intragastrically as an aqueous emulsion at a dose of
2.62 mmol/7.5 ml/kg.
Numbers of carbon atoms and
unsaturated
carbon-carbon
bonds are s h o w n in
parentheses.
A values represent the increment above
basal for the GIP response expressed as pg.ml-l.h,
calculated as described in the Results.
Values are
presented as means • SEM of 5-6 mice.
acid, and capric acid, a saturated medium-chain (C10:0) fatty acid,
did not significantly alter plasma GIP concentrations.
However, the
saturated and unsaturated long-chain fatty acids stearic acid (Clg:0),
oleic acid ( C l g : l ) , linoJeic acid (CIg:2) and linolenic acid (CIg:3)
produced a 3-#-fold elevation (P < 0.0l) of plasma GIP concentrations
between 60 and 120 rain. Mean increments above basal areas for the
GIP responses were calculated as the sum of values at 30-120 min
minus # times the basal value, and divided by 2 to give final expression as pg.ml-l-h.
The increments above basal were: propionic acid
691 -+ 350 (mean • SEM), capric acid 216 • 2gl, stearic acid 13#g •
#36, oleic acid 2399 • 392, linoleic acid 2550 +- 691, and linolenic acid
150g • 665. The GIP response to oleic acid was significantly greater
(P < 0.05-0.01) than the responses to prop•177 capric and stearic
acids, but not significantly greater than to linoleic and linolenic acids.
Discussion
Fat-stimulated GIP release is dependent on
of triglycerides and absorption of the digestion
GIP release is compromised in conditions of
such as cystic fibrosis and chronic pancreatitis
Ebert & Creutzfeldt, 19g0), and in the latter
pancreatic enzymes partially restore the GIP
intraluminaI hydrolysis
products. Accordingly,
impaired fat digestion
(Ross & Shaffer, 19gl;
condition extracts of
responses to oral fat
704
KWASOWSKI ET AL.
(Ebert & Creutzfeldt, lgg0).
In contrast, retardation of fat absorption with cholestyramine impairs GIP release (Ebert & Creutzfeldt,
t980).
Previous studies on the relative importance of triglyceride
d i g e s t i o n p r o d u c t s in f a t - s t i m u l a t e d GIP r e l e a s e have produced
equivocal results.
Thus, medium-chain triglycerides, monoglycerides,
glycerol and both saturated and unsaturated long-chain f a t t y acids such
as palmitic, oleic and linoleic acids have all been reported to lack
stimulatory e f f e c t s on GIP release (Ross & Shaffer, 19gl; Williams et
al., 1991).
In the present study, oral administration of the short-chain and
medium-chain fatty acids, propionic (C3:0) and capric (CI0:0) acids,
failed to produce a significant GIP response. However, equimolar
a d m i n i s t r a t i o n of a long-chain saturated f a t t y acid (stearic acid,
CIg:0) and especially the long-chain unsaturated f a t t y acids (oleic
CI8:I, linoleic Clg:2, and linolenic C18.3 acids) produced a marked
GIP response.
Short-chain and medium-chain f a t t y acids are absorbed
m o r e r a p i d l y t h a n l o n g - c h a i n f a t t y acids, and the more potent
GIP-releasing unsaturated long-chain f a t t y acids are absorbed faster
than their saturated counterparts (Cl&ment, 1980; Thomson & Dietschy,
1981). This indicates that GIP release is not related only to the rate
of cellular uptake of f a t t y acids, an event which does not demand
energy expenditure (Cl6ment, 1980; Thomson & Dietschy, 198I). It is
t h e r e f o r e likely t h a t the stimulus for fat-induced GIP release is
generated during the intracellular handling and metabolism of f a t t y
acids. Short- and medium-chain f a t t y acids are transferred across the
intestinal epithelium without esterification. However, long-chain f a t t y
acids are conveyed to the smooth endoplasmic reticulum for esterification prior to incorporation into chylomicrons and exocytosis into the
intercellular compartment (Clement, 1980; Thomson & Dietschy, 19gl).
The GIP-releasing action of f a t t y acids may be coupled therefore to
the extent of esterification, an energy-consuming metabolic process
c o n f i n e d to l o n g - c h a i n f a t t y acids ( C l e m e n t , 1980; Thomson &
Dietschy, 19gl).
Previous studies on the mechanism of carbohydrates t i m u l a t e d GIP r e l e a s e have shown that only actively transported
sugars, such as glucose and galactose, stimulate GIP secretion (Sykes
et al., 19g0).
Thus there may be a common link between metabolic
and secretory events responsible for nutrient-regulation of GIP release
from the intestinal K-cells.
References
Bailey CJ, Flatt PR & Atkins TW (1982) Influence of genetic
background and age on the expression of the obese hyperglycaemic syndrome in Aston ob/ob mice. Int. J. Obes. 6,
11-21.
Brown JC (1982) Gastric Inhibitory Polypeptide. Monographs on
Endocrinology, vol. 24, pp 1-88, Springer-Verlag, Berlin.
Brown JC, Dryburgh JR, Ross SE & Dupre J (1975) Identification
and actions of gastric inhibitory polypeptide. Recent Prog.
Horm. Res. 31, 487-532.
Cl6ment J (1980) Intestinal absorption of triglycerols. Reprod.
Nutr. Develop. 20, 1285-1307.
FATTY
ACIDS
AND
GASTRIC
INHIBITORY P E P T I D E
705
Creutzfeldt W (1982) Gastrointestinal peptides - role in
pathophysiology and disease. Scand. J. Gastroenterol. 17,
suppl. 77, 7-20.
Ebert R & Creutzfeldt W (1980) Decreased GIP secretion through
impairment of absorption. In: Frontiers in Hormone Research,
vol 7, pp 192-201 (Creutzfeldt W, ed), Karger, Basel.
Falko JM, Crockett SE, Cataland S & Mazzaferri EL (1976) Gastric
inhibitory polypeptide (GIP). Intestinal distribution and
stimulation by amino acids and medium chain triglycerides. J.
Clin. Endocrinol. Metab. 41, 260-265.
Flatt PR & Bailey CJ (1981) Abnormal plasma glucose and insulin
responses in heterozygous lean (ob/+) mice. Diabetologia 20,
573-577.
Flatt PR, Bailey CJ, Kwasowski P, Swanston-Flatt SK & Marks V
(1983) Abnormalities of GIP in spontaneous syndromes of
diabetes and obesity in mice. Diabetes 32, 433-435.
Flatt PR, Bailey CJ, Kwasowski P, Page T & Marks V (1984) Plasma
immunoreactive gastric inhibitory polypeptide in obese
hyperglycaemic (ob/ob) mice. J. Endocrinol. IO1, 249-256.
Marks V & Morgan LM (1984) The enteroinsular axis. In: Recent
Advances in Diabetes, vol I, pp 55-71 (Nattrass M & Santiago
JV, eds), Churchill Livingstone, Edinburgh.
Morgan LM, Morris BA & Marks V (1978) Radioimmunoassay of gastric
inhibitory polypeptide. Ann. Clin. Biochem. 15, 172-177.
O'Dorisio TM, Cataland S, Stevenson M & Mazzaferri EL (1976)
Gastric inhibitory polypeptide (GIP). Intestinal distribution
and stimulation by amino acids and medium chain triglycerides.
Am. J. Dig. Dis. 21, 761-765.
Polak JM, Pearce AGE, Grimelius L & Marks V (1975)
Gastrointestinal apudosis in obese hyperglycaemic mice.
Virchows Arch. (Cell. Pathol.) 19, 135-150.
Ross SA & Shaffer EA (1981) The importance of triglyceride
hydrolysis for the release of gastric inhibitory polypeptide.
Gastroenterology 80, 108-111.
Sykes S, Morgan LM, English J & Marks V (1980) Evidence for
preferential secretion of gastric inhibitory polypeptide in the
rat by actively transported carbohydrates and their analogues.
J. Endocrinol. 85, 201-207.
Thomson ABR & Dietschy JM (1981) Intestinal lipid absorption:
major extracellular and intracellular events. In Physiology of
the Gastrointestinal Tract, vol 2, pp 1147-1220 (Johnson LR,
ed), Raven Press, New York.
Williams RJ, May, JM & Biebroeck JB (1981) Determinants of
gastric inhibitory polypeptide and insulin secretion.
Metabolism 30, 36-40.