Bioscience Reports 2, 391-395 (1982)
Printed in Great Britain
391
O x y n t o m o d u l i n ( g l u c a g o n - 3 7 or b i o a c t i v e e n t e r o g l u c a g o n ) :
A p o t e n t i n h i b i t o r of p e n t a g a s t r i n - s t i m u l a t e d a c i d
s e c r e t i o n in r a t s
M. DUBRASQUET, D. BATAILLE* & C. GESPACH**
INSERM UIO, H6pital Bichat, 75877 Paris Cedex 18, France;
*Centre CNRS-INSERM de Pharmacologie-Endocrinologie,
B.P. 5055, 34033 Montpellier; and **INSERM U55, H~pital
St. Antoine, 75571 Paris Cedex 12, France
(Received 25 May 1982)
The action of oxyntomodulin and glucagon on pentagastrin-stimulated gastric secretion from the perfused
r a t s t o m a c h h a v e been c o m p a r e d :
both hormones
inhibit secretion in a dose-dependent manner.
In the last decade, it has been suggested that glucagon and/or 'gut
glucagon-like immunoreactive peptides' may play a physiological role in
t h e r e g u l a t i o n of gastric acid secretion (1,2).
We have recent l y
JLsolated from the distal small bowel a 37-amino-acid glucagon-related
peptide r e f e r r e d to as 'bioactive enteroglucagon' or glucagon-37 (3,4)
th at displayed a tissue specificity at the gastric level.
Indeed, in
co n tr as t to its lower potency versus glucagon in liver, this peptide was
about 20 times more potent than glucagon in stimulating cyclic AMP
in isolated rat fundic glands (5).
Accordingly, we proposed to call
this peptide 'oxyntomodulin' (5).
The purpose of the present work was to compare the action of
oxyntomodulin and glucagon on the stimulated gastric acid secretion in
the rat. We used the perfused stomach in the anest het i zed rat, which
seems suitable to study the inhibition caused by drugs of stimulated
acid secretion (6).
M a t e r i a l s and M e t h o d s
Operative technique
Male Wistar rats weighing 300 +- 25 g were fasted for Ig h before
experiments but were allowed access to water.
The technical aspects
of the operation have been described by Ghosh and Schild and modified
by Lai (7). The rats were anesthetized with urethane (0.6 to 0.7 ml
of a 25% solution per 100 g) given by intramuscular injection.
A polyethylene c a t h e t e r , introduced into the oesophagus and passed
to t h e l e v e l of the cardia, was connected to a peristaltic pump
(Desaga) set to deliver a solution of 0.9% NaCI at a constant rat e of
0.8 to 1.0 m l / m i n.
The perfusate was collected through another
c a t h e t e r p l a c e d t h r o u g h the pylorus and secured with a ligature.
Whenever necessary, the t e m p e r a t u r e of the rats was maintained at
34~ with the aid of el ect r i c lamps.
01982
The Biochemical Society
392
DUBRASQUET
ET
AL.
A 0.5-mm butterfly c a t h e t e r was introduced into the dorsal vein of
the penis in order to infuse the stimulants. A 0.45-mm needle joined
to a 602-105 silastic tube was introduced into a fundic branch of the
coeliac ar t er y, thus permitting direct injection of the substances to be
t e s t e d into the fundic area.
Pharmacological agents and doses used
Pentagastrin (Peptavlon ICI) 0.125 iJg.kg-t-h-l; histamine (Sigma)
1.5 m g . k g - t ' h - t ; glucagon (Novo, Copenhagen) 0.3 to # nmol.kg-t;
o x y n t o m o d u l i n ( B a t a i l l e et al., submitted) 0.01 to 0.2 nmol-kg-t;
somatostatin (Clin Midy, France) 1.2 nmol.kg-l. The last t hree agents
were dissolved in 0.1 ml of saline.
Experimental protocol
The tests were begun a f t e r stabilization of the gastric perfusion,
usually within 30 to 60 rain a f t e r completion of the surgical preparation. The gastric secretion, diluted with the perfusate of 0.9% NaC%
was collected every 20 rain and the acidity was measured by titrating
the entire sample with 0.01 N NaOH to the phenolphthalein end-point.
Pentagastrin and histamine were infused at a rat e of 2.4 ml.h-t. The
plateau stimulation was obtained 1.5 h aft er the beginning of infusion.
Glucagon and oxyntomodulin were carefully administered as a 0.1-ml
bolus and the c a t h e t e r rinsed with 0.1 ml of saline9 The injections,
p er f o r med in random order, were separated by an interval of 2 h.
Each experimental group consisted of 5 or 6 rats, and 98 rats were
used for the present study 9
Expression of results
C h a n g e s in gas t r i c secretion were evaluated during the 40-min
period following injection and expressed as % of inhibition, the plateau
value being taken as the r e f e r e n c e .
Results
Gastric-acid secretion induced by pentagastrin was readily inhibited
by both glucagon and oxyntomodulin.
A linear log-dose e f f e c t was
obtained for both (see Fig. I)
The apparent ID 0 were 1 26 and
0.096 nmol'kg -1 body wt. for glucagon and oxyntomoduhn, respectively.
As l i t t l e as 10 p m o l . k g -I oxyntomodulin was able to produce a
significant e f f e c t (see Fig. l ) .
Table 1 displays the comparative e f f e c t of oxyntomodulin, glucagon,
and s o m a t o s t a t i n on p e n t a g a s t r i n - and h i s t a m i n e - s t i m u l a t e d acid
secretion.
A t doses where the t hr e e peptides were able to produce a
50% inhibition when pentagastrin was the stimulant, the decrease in
histamine-induced secretion was less than 10% for the peptides of the
glucagon family and not significant for somatostatin.
9
5
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9
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O X Y N T O M O D U L I N AND ACID S E C R E T I O N
393
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Fig. i.
Dose-effect of oxyntomodulin (G-37) and
pancreatic
glucagon
(G-29) on pentagastrinstimulated gastric acid secretion in anesthetized
rat.
Data (means +_ S.E.M.) are expressed as % of
inhibition as a function of the amount (in nmol/kg
body wt.) of peptide injected
(see 'Materials and
Methods'); the plateau value obtained with the
perfusion of pentagastrin was taken as the reference
(0%).
The dotted line represents the observed 50%
inhibition used for estimating the ID50 for both
peptides (see results).
The number of experiments
performed with each dose of peptide is indicated
near each experimental point.
Table i. Comparative effects of oxyntomodulin~ glucagon~
and somatostatin~ at dosage levels inhibiting by 50%
the pentagastrin-stimulated secretion~ on histaminestimulated secretion
]Means + S.E.M., n = 7.
Inhibition (%) of
pentagastrinstimulated secretion
Inhibition (%) of
histaminestimulated secretion
Oxyntomodulin
0.086
50
9.6 _+ 0.6
Glucagon
1.26
50
6.2 + 2.2
Somatostatin
1.2
50
Drug and dose
(nmol/kg)
5
39/4-
DUBRASQUET
ET
AL.
Discussion
The p r e s e n t d a t a c l e a r l y show that, in anesthetized rat, both
p a n c r e a t i c g l u c a g o n and a newly isolated glucagon-like intestinal
peptide, oxyntomodulin, are able to inhibit pentagastrin-stimulated acid
secretion in a dose-dependent manner.
On a molar basis, oxyntomodulin is, in our experimental conditions, 10-20 times more potent
than glucagon.
It is noteworthy that a similar ratio between the
potencies of the two peptides has been previously observed in gastric
glands isolated from the rat oxyntic area (5), which suggested the
presence in those glands of a specific oxyntomodulin-sensitive system
(5,8).
The p r e s e n t data strongly support the idea (3) that the
g l u c a g o n - r e l a t e d p e p t i d e s are o p e r a t i v e t h r o u g h this system on
p e n t a g a s t r i n - s t i m u l a t e d acid secretion.
The existence of a direct
e f f e c t of these peptides on the oxyntic glands is further supported by
the fact that 5-10 times lower doses oi either glucagon or oxyntomodulin are necessary when injected in situ (fundic branch of the
coeliac artery) than when injected in systemic blood (data not shown).
The quantitative ultrastructural changes and the increase in gastric
potential difference induced by glucagon (9) could be facilitated by
this local administration.
Our d a t a on histamine-stimulated gastric acid secretion are in
a g r e e m e n t with the results obtained by Wilson (10); they should,
however, be examined in light of the poor e f f e c t of peptides on this
secretion, which is well documented in the case of somatostatin (6).
It has been suggested that 'enteroglucagon' released during the
intestinal phase of digestion plays a role in the regulation of gastric
secretion (l 1).
The glucagon-like intestinal peptide involved could
well be oxyntomodulin.
Indeed, the e f f e c t of low doses of oxyntomodulin on g a s t r i c - a c i d s e c r e t i o n evidenced by the present data
t o g e t h e r with with t h e predominance of this peptide among the
glucagon-like bioactive peptides in porcine (4) and human (12) gut
argue in favor of this regulatory function.
A l t h o u g h the p r e c i s e mechanisms involved in the inhibition of
gastric secretion by oxyntomodulin have to be explored more deeply
both from a physiological and a biochemical point of view, our data
suggest that this intestinal peptide plays a key role in the regulation
of the intestinal phase of gastric secretion.
References
i. Christiansen J, Hoist JJ, Kalaja E (1976) Inhibition of
gastric acid secretion in man by exogenous and endogenous
pancreatic glucagon. Gastroenterology 70, 688-692.
2. Konturek SJ, Biernat J, Kwiecie6 N & Oleksy J (1975) Effect of
glucagon on meal-induced gastric secretion in man.
Gastroenterology 68, 448-454.
3. Bataille D, Gespach C, Tatemoto K, Marie J-C, Coudray A-M,
Rosselin G & Mutt V (1981) Bioactive enteroglucagon (oxyntomodulin): Present knowledge on its chemical structure and its
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O X Y N T O M O D U L I N AND ACID SECRETION
395
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Mutt V (1982) Isolation and chemical characterization of
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