Mechanism of motilin-induced contractions in isolated perfused canine stomach

1993;105:425-432

GASTROENTEROLOGY

Mechanism of Motilin-Induced Contractions in Isolated Perfused Canine Stomach AKIYOSHI MIZUMOTO,* ISAMU and KIHACHI OHSHIMA* *Gastrointestinal

Laboratories,

SANO,*

Institute of Endocrinology,

YUGO

MATSUNAGA,*

and *First Department

OSAMU

examined

It

accordingly,

is well known

in initiating

fasted humans nism

that motilin

phase III contractions and dogs; however,

of the action

of motilin

because of conflicting in vitro experiments, example,

plays an important

motilin

role

in the stomach the detailed

is not yet clear

of

mechamainly

results obtained in in vivo and including species difference. For

contracts

human

and rabbit

muscle

strips in vitro by acting directly on motilin receptors located on smooth muscle cells but has no effect on canine muscle strips. l-3 On the other hand, motilin’s action in vivo is inhibited by anticholinergic agents in humans and dogs,4,5 indicating that motilin acts through cholinergic neural pathways. To examine the mechanism of action of peptides or drugs, experiments on isolated perfused intestine are an extremely useful method. Several investigators have

the mechanism

of this system. canine

Hirning

intestine,

creased

ITOH,*

injection

pressure,

which and

On the other hand,

that motilin-induced

lated canine atropine.’ isolated tractions

jejunum

through

of mucosal activity

tetrodotoxin,

in the isobut not that in

motilin

initiates

phasic

mediated (5-HT)8

receptors

but et al.

by naloxone,

the cholinergically

that 5-HT,

in-

was antagonized

et al. reported

5-hydroxytryptamine

suggested

that in the

of motilin

contractions

Kellum

by means

Fox-Threlkeld

ileum were inhibited Furthermore,

canine

action

and Burks reported

hexamethonium,

not naloxone.6 showed

of motilin’s

intra-arterial

intraluminal

by atropine,

mediate

conrelease

and further

the contractile

of motilin.”

However,

it is considered

that

originate

duodenum Namely,

in

lin antiserum phase

III

are

inhibits

motilin

the phase

and

the

independent. are closely

peak,“,”

and moti-

III contractions

only

but does not affect the occurrence originating

Therefore,

the main

site of action

mans

dogs

is considered

in the stomach

seems

the properties

ing

effect

in the

Cook et all3 and Green

of

in the jejunum.12 of motilin

in hu-

to be in the stomach;

to clarify the mechanism

understanding motilin’s

III contrac-

in dogs

motilin

contractions

and

phase

phase III contractions

with the plasma

in the stomach

that

in the jejunum

humans

only gastric

associated

tilin

ZEN

of Internal Medicine, Gunma University, Maebashi, Japan

Back&ound: Motilin is known to induce gastric phase III contractions via neural pathways in vivo, but the local mechanism of action is not clearly determined. Methods: An isolated perfused canine stomach was used to demonstrate the mechanism of motilin. Synthetic canine motilin at doses of 0.1,0.3, 1.O, and 3.0 pg/h was infused intra-arterially, and effects of several receptor antagonists on motilin-induced contractions were examined. Results: The immunoreactive motilin concentration of venous effluent showed that motilin at doses of 0.1 and 0.3 yg/h was within the physiological range. Each dose of motilin induced phasic contractions in the isolated stomach, and a doserelated increase in frequency was observed, but not their mean amplitude. Atropine, hexamethonium, ICS205-930, BRL43694, phentolamine, yohimbine, and propranolol significantly inhibited motilin-induced contractions. Naloxone, methysergide, and timolol did not affect the response of motilin. Prazosin significantly increased the mean amplitude of motilin-induced contractions. Conclusions: Physiological dose of motilin can initiate phasic contractions in the stomach independently of the presence of the extrinsic nerves. The results suggest that cholinergic pathway, 5hydroxytryptamine (HT), receptors, and a receptors are involved in the motilin-induced contractions.

tions

YAMAMOTO,*

of action

to be very

important

of this peptide. canine

isolated

et a1.14 reported

of moin

Concernstomach,

that intra-arte-

rial bolus injection of motilin stimulated isolated canine stomach motility and that motilin-induced contractions

were inhibited

by atropine,

hexamethonium,

and tetrodotoxin. However, a pharmacological dose of motilin was used in these studies, and it is not clear whether a physiological dose of motilin can stimulate gastric motor activity in an isolated stomach. The aim of the present study was to examine the relationship between the effects of motilin on the isoAbbreviations used in this paper: 5-HT, 5-hydroxytryptamine. 0 1993 by the American Gastroenterological Association 0016-5085/93/$3.00

426

MIZUMOTO

lated perfused

ET AL.

GASTROENTEROLOGY

stomach

and the motilin

and to show the mechanism detail

by using

several

of the action

concentration of motilin

in

antagonists.

Materials and Methods Preparation Stomach

of the isolated Perfused

Twenty-five mongrel dogs of either sex weighing 6.5-9 kg were anesthetized with sodium pentobarbital (30 mg/kg intravenously). The procedure for isolation of the stomach was as follows. After laparotomy, the continuity of the stomach with the esophagus and duodenum was interrupted at positions 1 cm proximal to the lower esophageal sphincter and 1 cm distal to the pyloric ring, respectively. When splenectomy was performed, the short gastric vessels were preserved. The great and lesser omentum were ligated and resected. The splenic vein was isolated from the pancreas, the celiac trunk was exposed, and the common hepatic artery was ligated and resected. After the complete isolation of the stomach, the celiac artery and splenogastric vein were cannulated (Atom Intravenous Catheter, 5F, Atom Co. Ltd., Tokyo, Japan), and the stomach was perfused through the celiac artery with a peristaltic pump (Harvard Apparatus, MA) at a speed of 20 mL/min. A gastric tube was inserted into the stomach to drain out gastric juice during the experiments. The perfusate was composed of Krebs-Henseleit bicarbonate buffer containing 3% bovine serum albumin (Fraction V; Boehringer Mannheim Yamanouchi Co. Ltd., Tokyo, Japan), 20% thoroughly washed human erythrocytes, and glucose at a concentration of 100 mg/dL, as reported by Chan and Dehaye. l5 The perfusate was maintained at 37’C in a water bath and gassed with 95% 0, and 5% CO,.

Measurement

of Gastric Contractions

To record and measure gastric contractions, two strain gauge force transducers were sutured onto the serosal surface of the gastric body (4 cm distal to the lower esophageal sphincter) and the gastric antrum (4 cm proximal to the pyloric ring) to detect circular muscle contractions. The lead wires of these transducers were connected to an amplifier (UG-5; Nihon Kohden Kohgyo Co., Tokyo, Japan), and the signals from the amplifier were recorded on a multichannel pen-writing recorder (WI-681G; Nihon Kohden Kohgyo) and data recorder (RCM Data Recorder; TEAK Corp., Tokyo, Japan) for further analysis of the data.

Experimental

Procedures

After a 60-minute equilibration period, synthetic canine motilin (Peptide Institute Inc., Osaka, Japan) at a dose of 0.1,0.3, 1.O, or 3.0 pg/h was infused continuously for 10 minutes into the arterial cannula with an infusion pump (STC-521; Terumo, Tokyo, Japan). Each dose of motilin was tested eight times. Blood samples (0.9 mL) were collected from the venous cannula at 2-minute intervals in a

Vol. 105,

No. 2

heparinized syringe containing 0.1 mL of aprotinin (Trasy101, 10,000 kallikrein U/mL; Bayer Japan, Tokyo, Japan) and were immediately centrifuged at 3000 rpm for 15 minutes. The supernatants were separated and stored at -30°C until the radioimmunoassay for motilin. Details of the assay procedure were reported previously.‘6 To examine the mechanism of action of motilin, the following drugs were used: atropine (muscarinic-receptor antagonist); hexamethonium (nicotinic-receptor antagonist); naloxone (opiate-receptor antagonist); methysergide (5HT,- and 5-HT,-receptor antagonist); ICS 205-930 (5HT,- and 5-HT,-receptor antagonist); BRL43694 (5-HT, receptor antagonist); phentolamine (a-receptor antagonist); prazosin ((&-receptor antagonist); yohimbine (a,-receptor antagonist); and propranolol and timolol (P-receptor antagonists). Each drug except for atropine was tested at a dose of 10 mg/h, and atropine was used at a dose of 1 mg/h. Ten minutes after the infusion of the antagonist, motilin at a dose of 0.3 l.tg/h was infused for 10 minutes, and the contractile activity with or without pretreatment with antagonists was compared. Each drug was tested six times.

Analysis of Data The contractile activity of motilin was assessed by its frequency and mean amplitude. The number of contractions induced by motilin for 10 minutes was counted, and the frequency was expressed as contractions per minute. From when the contractile wave increased from the basal tone to when it returned to the basal line was defined as one contraction. The mean amplitude was determined by dividing the sum of the amplitude of each contraction by the number of contractions and expressing the result in grams. Each force transducer was calibrated before the experiment.

Drugs Atropine sulfate, hexamethonium bromide, naloxone hydrochloride, phentolamine mesylate, prazosin hydrochloride, yohimbine hydrochloride, propranolol hydrochloride, and timolol maleate were obtained from commercial sources. Methysergide and ICS205-930 were kindly donated by Sandoz Pharmaceuticals (Basel, Switzerland). BRL43694 was a gift from Beecham Pharmaceuticals (Harlow, Essex, England). Prazosin and yohimbine were dissolved in dimethyl sulfoxide, and the others were dissolved in normal saline.

Statistics Results were expressed as mean + SE. The data for the dose response experiment on motilin were assessed by one-way analysis of variance (ANOVA) following the Scheffe F test. In the case of the antagonist study, the paired t test was used. A P value < 0.05 was considered significant.

Results Both the gastric body and antrum showed phasic contractions in the resting state. The frequency of

MECHANISMOF MOTILIN-INDUCEDCONTRACTIONS 427

August 1993

spontaneously

occurring

contractions

in the

3

-

*z 2 _

-

gastric

body (0.52 & O.Ob/min) was significantly greater than that in the gastric antrum (0.27 rf: O.O4/min). Motilin at a dose of 0.1 lug/h of 8 occasions;

induced

they were clearly

spontaneously

occurring

lin 20.3

always

l.rg/h

the perfused tilin

stomach

shortened

motilin

(Figure

(Figure

Doses of moti-

phasic

contractions

1). Graded

in

doses of moof the

and the onset of motilin-induced

con-

2). Figure

tions.

In the gastric

body,

the effect

E ._ I-

1

-

contrac-

of motilin

was

the basal level was observed

1.0

0.3

3.0

Dose of motilin, pg/hr

at doses of

Figure 2. Time lag between the initiation of motilin infusion and the onset of contractions. Graded doses of motilin shorten the time lag in a dose-dependent manner (n = 8).

I

I

0.1

and a significant

Motilin, 0.3 pg/hr Gastric

9

3 shows the dose response

of motilin-induced

from 0.1 to 1 .O pg/h,

from

from

initiation

for the frequency

dose dependent

on 5

distinguishable

contractions. induced

curve

increase

contractions

the time lag between

infusion

tractions

phasic

Body

motilin Gastric Antrum

20.3

pendent

yg/h.

increase

In the gastric in frequency

antrum,

0.1 to 3.0 l.~g/h, and all doses of motilin

Motilin, 1.Opg/hr Gastric Body

I

1

at from

increased

the

frequency

significantly

compared

with that in the rest-

ing state.

Concerning

the mean

amplitude,

dose of 0.3 l.~g/h did motilin

Smin

a dose-de-

was observed

tude

above

body

and antrum.

induced tions.

strong This

amplitude, the gastric

increase

the basal contractions contractions

dose therefore and a significant antrum (Figures

followed tended

at a

the mean ampli-

in both

A dose of 3 &/h

only

the gastric

motilin

initially

by weak contrac-

to reduce

the mean

decrease was observed 1 and 4).

in

Ga

I

h

19

5 mln

2.0 -0-

Gastric Body

+

Gastric Antrum

Motilin, 3.0 Fglhr Gastric Body

r

I

Gastric Antrum 0.5(I

J

I

5mln Figure 1. Effect of intra-arterial infusion of synthetic canine motilin on isolated perfused stomach. Each dose of motilin induced phasic contractions both in the gastric body and antrum.

II

I

0.1

0.3

1.0

3.0

Dose of Motilin, pg/hr Figure 3. Frequency of motilin-induced contractions. *P < 0.05 compared with the frequency of spontaneously occurring contractions in the resting state (n = 8).

428

MIZUMOTO ET AL.

GASTROENTEROLOGY Vol. 105, No. 2

10 -

*

-0-

Gastric Body

however,

--O-

Gastric Antrum

chol-induced

8-

g

$ . 3 .t=

and

8-

$4-

did not inhibit

timolol

significantly.

duced

transient

affect

the mean amplitude

tractions

(Figure

6; Table

contrac-

with

contractions

increased

between

methysergide,

motilin-induced

Pretreatment phasic

of bethane-

Naloxone,

prazosin

in-

and significantly

of motilin-induced 2). There

con-

was no regional

the gastric body and gastric

antrum

in the effect of each antagonist.

s

2-

*

basal

0.1

0.3

1.0

Discussion Controversies

3.0

ously,

Figure 4. Mean amplitude of motilin-induced contractions. *P < 0.05 compared with the mean amplitude of spontaneously occurring contractions in the resting state (n = 8).

nerve

duced

phase

concluded

motilin

The

concentration

the basal condition administration

motilin

increased

162 f

33 pg/mL,

pg/h

to 1746 f

pg/mL.

Because

the plasma

the normal

and 3 l.rg/h

cal range.

was confirmed

III

Atropine, yohimbine, occurring

studies

induced

resting

state and significantly

transient

plitude

of the spontaneously

thegastricbody(8.9+1.1~~.

used in

BRL43694,

spontaneously

but phentolamine,

Administration phasic

ti-

of prazosin

contractions

increased occurring

such

al. showed

stomach.” vagal

of motilin perfused

initiates

in the am-

contractions

in

11.7+1.2g,P
phasic

stomach

denervated

pouch”,‘”

et

diaphragmatic

of gastric

phase

a physiological

contractions that

or a

Gleysteen

at the

that

suggests

On the

III dose

in the isolated

the presence

of the

vagus nerve is not essential for the occurrence of motilin’s action and supports the concept that motilin acts as a physiological

hormone. stomach

dent effect on frequency. spontaneously conscious

occurring

dogs (about

cally treated normal

had a dose-depenfor each dose

isolated

curve

phase

III

stomach

between to motilin.

amplitude

was bell shaped.

in

The reathe surgi-

and the stomach

in reactivity

for the mean

contractions

contractions

2 contractions/min).

on the difference

conditions

response duced

motilin

The frequency

used in this study was lower than that of the

son may depend

the mean

extrinsic

cooling

and

phase III-like

Furthermore,

finding

motilin-in-

integrity.” initiates

level did not affect the occurrence ” Our

of the

in the stomach

as an autotransplanted

that

contractions.

cooling and

III contractions motilin

the Previ-

in the stomach

a chronically

isolated

of motilin

did not affect the

spontaneous

vagosympathetic

In the isolated

abolished

and naloxone

always

0.3 pg/

was, therefore,

contractions,

significantly.

in

the physiologi-

ICS205-930,

and propranolol phasic

moti-

antagonists.

hexamethonium,

methysergide,

contractions

with

1

contractions

to be within

This dose of motilin

the following

to

to >3200

range of the plasma phase

totally

concerning

of motilin.

that cervical

contractions

exogenous in

stomach,

to 338 * 29 pg/mL,

223 pg/mL,

require

hand,

contractions

canine

concentration

dogs was from 200 to 1000 pg/mL,

h of motilin

molol,

of synthetic

motilin

0.3 yg/h

during

effluent

was only 0.5 +- 0.2 pg/mL.

of 0.1 pg/h

concentration

conscious

in the venous

inhibited III-like

that phase

normally The

in the action

Hall et al. reported

vagus

other during

have been raised

role of the vagus nerve

Dose of Motilin, pg/hr

lin

did not

tions

difference

5

the occurrence

contractions.

under

The dose

of motilin-in-

This may explain

The effects of each antagonist on the frequency and mean amplitude of motilin-induced contractions are shown in Tables 1 and 2, respectively. Atropine, hexamethonium, ICS205-930, BRL43694, yohimbine, and

the observation reported by Otterson and Sarna in which high doses of erythromycin, a motilin receptor agonist,** prolonged the cycle length of phase III con-

propranolol significantly decreased both the frequency and mean amplitude of motilin-induced contractions. In the case of phentolamine, the mean amplitude was significantly inhibited, but the frequency was not. A typical example of the effect of BRL43694 is shown in Figure 5. The administration of BRL43694 instantly inhibited spontaneously occurring phasic contractions and abolished motilin-induced contractions. BRL43694,

sia.23 Why motilin has no effect on canine gastric muscle strips in vitro is unknown. The differences between isolated stomach and muscle strips in vitro are whether motilin is given by an intra-arterial route and whether complete muscle and myenteric neural conHowever, motilin receptors nections are preserved. must exist in the stomach, and activation of motilin

tractions

and produced

amyogenesia

and dysmyogene-

MECHANISM OF MOTILIN-INDUCED

August 1993

Table 1. Effect of Antagonist on the Frequency of Motilin-induced

Atropine Hexamethonium Naloxone Methysergide ICS205-930 BRL43694 Prazosin Yohimbine Propranolol Timolol

Without (contractions/min)

1.23 + 0.26 0.84 1.12 1.58 1.20 1.32 0.90 0.95

f + + f + f f

Gastric antrum

With (contractions/min)

0.23 0.14 0.97 1.52 0.30 0.20 0.85 0.53

+ 0.1 5b f 0.06” + 0.27 f 0.31 x!z0.17= + 0.13* f 0.29 f 0.10 Ob 0” 1.23 + 0.14

0.14 0.20 0.29 0.34 0.22 0.14 0.13

1.10 Ii 0.12 1.55 + 0.40 1.2OkO.17

429

Contractions

Gastric body Motilin (0.3 pg/h)

CONTRACTIONS

Without (contractions/min)

With (contractions/min) Ob

0.92 + 0.22 0.68 f 0.10 0.65 T!Z 0.18 1.OO f 0.25 0.50 ir 0.11 0.62 + 0.05 0.83 +- 0.19 0.48 + 0.08 0.78 + 0.22 l.lOzkO.23 0.62 + 0.48

0.20 0.58 0.80 0.25 0.17 0.68

* 0.2oa f 0.2 1 f 0.23 + 0.14 f 0.1 lb + 0.43 0.30 Oa 0” 0.62 + 0.48

NOTE. Results are expressed as mean + SE; n = 6. Atropine was used at a dose of 1 mg/h and the others at 10 mg/h. aP < 0.05, bP < 0.01 compared with the value without antagonist.

ceptor antagonist on motilin-induced contractions was also reported by Kuemmerle et al. in the isolated perfused canine jejunum.” We have already reported that 5-HT,-receptor antagonists strongly inhibited spontaneous and motilininduced phase III-like contractions in the vagaily innervated stomach but not in the chronically denervated stomach, suggesting that the vagus nerve plays an important role in an inhibitory effect of 5HTs-receptor antagonists on motilin-induced contractions.25 However, the p resent study showed that 5-HT, receptors in the stomach also play an important role in the occurrence of motilin-induced contractions. The conflict between the results of the previous and present studies may be caused by the different experimental designs; one possibility is that in a chronically denervated pouch, motilin becomes able to induce gastric contractions via other pathways that are independent

receptors results in the excitation of myenteric cholinergic neurons, because atropine and hexamethonium almost completely inhibited the motilin-induced contractions. Besides the anticholinergic agents, two different 5HT, receptor antagonists used in the present study also abolished the motilin-induced contractions. Although ICS205-930 has been reported to have an antagonistic activity on not only 5-HT, but also 5-HT, receptors at high concentrations, 24BRL43694 alone completely inhibited motilin-induced contractions. This finding suggests that 5-HT, receptors are mainly involved in the occurrence of motilin-induced gastric contractions. Because 5-HT,-receptor antagonists did not affect bethanechol-induced contractions, it is suggested that these drugs have no effect on muscarinic receptors and have no nonspecific inhibitory effects on smooth muscle cells. Such an inhibitory effect of 5-HT,re-

Table 2. Effect of

Antagonist

on the Mean

Amplitude of Motilin-Induced

Contractions

Gastric body Motilin (0.3 ug/h) Atropine Hexamethonium Naloxone Methysergide ICS205-930 BRL43694 Phentolamine Prazosin Yohimbine Propranoiol Timolol

Without (g) 4.4 + 1.4 4.3 f 1.6 8.3 6.2 9.6 9.7 14.4 8.1 13.2 13.8 8.8

f f + ” k f -t + +

1.5 2.1 1.4 1.8 3.7 1.4 4.2 4.4 0.6

Gastric antrum With (g) 0.2 1.9 8.2 4.6 0.7 0.5 3.2 14.2

* 0. la k 1.V + 1.7 f 1.2 f o.4a + o.3b f 0.7’ + 2.2a 0” oa 6.8 + 1.o

Without (g)

1.1 + 0.6 f 1.7 f 1.1 + 2.4 Ik 1.3 f 3.2 f 1.8 f 3.0 + 3.3 + 0.6

4.0 f

5.6 6.7 3.2 8.1 5.9 9.8 9.1 7.6 6.2 11.6

NOTE. Results are expressed as mean + SE; n = 6. Atropine was used at a dose of 1 mg/h and the others at 10 mg/h. aP < 0.05, bP < 0.01 compared with the value without antagonist.

With (g) Oa 0.2 + 0.2b 7.1 + 1.2 3.1 f 1.1

0.8 0.5 0.9 16.6

rf. 0.5a f 0.3= f 0.5a f 4.4a Oa O8 8.5 k 1.3

430

MZUMOTO

ET AL.

GASTROENTEROLOGY

Motilin, 0.3 Cls/hr

Be4hanechol, 0.5 mg

I*

r BRL 43694,lO mglhr

1g

influence

the response

be caused

by the different

organs

However,

it is considered

that opiate

responsible

site of action

gastrointestinal

5 mln

creased

Figure 5. Effect of pretreatment with BRL43694 on motilin-induced contractions. BRL43694 abolished not only spontaneous but also motilin-induced contractions, but it did not inhibit the occurrence of bethanechol-induced contractions.

the duration

spite of the increase Furthermore,

of 5-HT,

receptors.

that novel renergic

Andrews

alterations

in cholinergic

function,

systems,

and sympathetic

have

been

long-term

vagotomy.

shown

study

HT,

receptors

times

were

that

antagonists

not enough

completely. BRL43694

like contractions Therefore,

to block

inhibit

isolated

vated pouch

peripheral

vagal denervation lin’s action

ticipates

tractions.

On

the

other

antagonist, in

report)

phase III-

denervated

5-HTs-receptor

pouch.

antagonists

in the acutely

but not in chronically

in forming

et al. have suggested

de-

dener-

increased duced

the

lin’s action

the We

force

CY. blockers

a,-receptor

a selective

of

results

phasic

significantly motilin-in-

indicate

that

for the occurrence

of the

an-

act as a factor gastric

because phentolamine

con-

transient and

amplitude These

a

inhibited

prazosin, state

III

contractions.

motilin-induced

hand,

and a, receptors

contractile

However,

of phase

phentolamine,

a selective

induced

are responsible

in

that phentol-

significantly

resting

mean

contractions.

receptors the

the

the

guanethidine

a2

of motiinhibiting

smooth

muscle.

and yohimbine

are re-

that chronic

pathways

of moti-

new pathways

that

Motllin, I

0.3p@hr I

one in the enteroneurons,

of motilin-induced

release of 5-HT from enterochromaffin

did

study,

inhibited

in-

of contractions.29

et al. report

that yohimbine, completely

$-receptor

cells or one in the myenteric

Kellum

and found tagonist,

are

and the

the effects of selective

contractions

affects the neural

in the occurrence

examined

reports

III contractions

of motilin-induced

(five

are independent of 5-HT, receptors. It remains uncertain which 5-HT, chromaffin

therefore

of phase

blocker,

con-

to the first possibility:

and results

5-

a

con-

III.27,28 On that

on the occurrence

we further

However,

contractions

stomach

points

is that the

and motilin-induced

motilin-induced

nervated

after

phase

In the present

amplitude

study

III contractions

in the number

had no effect

nonselective mean

is in the upper

Previous

et al. report

at doses up to 5 mg/kg

in the chronically

the fact that

in-

used in the pre-

as large as that used in the previous

not affect spontaneous

tions.

stomach

26 The other possibility

doses of 5-HT,receptor vious

in ferret

nonad-

be-

show that phentolamine

El-Sharkawy

contractions.30

reported

noncholinergic

nervation

firmed

and Bingham

are not

of motilin,

in the present

during

Ormsbee

the occurrence

amine

receptors

action

of motilin

of phase

amplitude

hand,

inhibits

may

used in these studies.

antagonists.

Some reports

contractile other

finding

the a-receptor

conflicting.

No. 2

tract.

interesting

cerned

The difference

for the physiological

cause the main An

of motilin.

Vol. 105,

par-

contrac-

that intraluminal cells is respon-

sible for the occurrence of motilin’s action in canine isolated jejunum.* In contrast to 5-HT, receptors, 5-HT, and 5-HT, receptors are considered to be independent of motilin’s action, because methysergide had no effect on motilin-induced contractions. Fox-Threlkeld et al. reported that motilin-induced contractions in the canine isolated ileum are atropine insensitive but naloxone sensitive, suggesting that opiate receptors are involved in the occurrence of motilin-induced contractions.’ However, our results and Hirning and Burks’ report6 show that naloxone did not

Figure 6. Motilin-induced contractions with or without pretreatment with prazosin in the same dog. Prazosin induced transient phasic contractions in the basal state and increased the amplitude of motilin-induced contractions.

MECHANISM OF MOTILIN-INDUCED

August 1993

ported

to have an antagonist

5-HT

effect on peripheral

the receptors, 31*32further study is needed to determine role of a2 receptors in motilin-induced contractions. Moreover,

our results

of previous tions

reports

of a-receptor

the dosage

suggest

subtypes,

or methods

Concerning

that

may be caused

including

spontaneous

It has been reported

has a local anesthetic

activity

and ti-

molol

does not.33 Furthermore,

timolol

more

potent

as an antagonist

than

propranolol

by

of muscle

electrical

shown). specific

and

volved

suggested

that

(data

not

the effect

contractions

that

in the occurrence

induced

vitro

considered

on motilin-induced

the con-

stomach

in

at p

concentra-

inhibited

of canine

stimulation

It is therefore

propranolol

at

completely

strips

field

is eight times

propranolol

receptors.% Moreover, tions of >10b6 mol/L tractions

in

proprano-

inhibited

contractions.

that propranolol

ac-

differences

antagonists,

completely

and motilin-induced

results

used in these studies.

the P-receptor

101, but not timolol,

conflicting

by the different

of

was non-

p receptors

are not

of motilin-induced

in-

contrac-

esophageal

The antagonists tions

than

more,

contractile

similar neural

observed

pathway

1986; 128:24 l-248. Daniel EE. Mechanism of noncholinergic excitation of canine ileal circular muscle by motilin. Peptides 199 1; 12: 1047- 1050. 8. Kellum JM, Maxwell RJ, Potter J, Kummerle JF. Motilin’s induction of phasic contractility in canine jejunum is mediated by the luminal release of serotonin. Surgery 1986;100:445-453.

9. Kuemmerle JF, Kellum JM. Serotonin neural receptors mediate motilin-induced motility in isolated, vascularly perfused canine jejunum. J Surg Res 1988;45:357-362. 10. Poitras P, Steinbach JH, VanDeventer G, Code CF, Walsh JH. Motilin-independent ectopic fronts of the interdigestive myoelectric complex in dogs. Am J Physiol 1980;239:G2 15-G220. 11. Bormans V, Peeters TL, Janssens J, Pearce D, VanDeweerd M, Vantrappen G. In man, only activity fronts that originate in the stomach correlate with motilin peaks. Stand J Gastroenterol 1987;22:781-784. 12. Lee KY, Chang TM, Chey WY. Effect of antimotilin serum on myoelectric activity and plasma motilin concentration in fasting dog. Am J Physiol 1983;245:G547-G553.

13. Cook MA, Kowalewski K, Daniel EE. Electrical and mechanical

contracFurther-

14. Green WER, Ruppin H, Wingate DL, Domschke W, Wonsch E,

by motilin

were quite

contractions

in isolated

In conclusion, stimulate trinsic

gastric

motor

regulated

pathways,

preganglionic

factor

and

inhibiting

spontaneously

independently

studies

ceptors

and the origin

concerning

can are

17.

as excitatory choliner-

are involved;

force, 01, receptors

of 5-HT

15. Chan TM, Dehaye JP. Hormone regulation of glucose metabolism

of ex-

contractions

pathways:

receptors

contractile

Further

doses

and postganglionic

5-HT,

volved.

These

16.

activity

by neural

Demling L, Ritchie HD. Effects of 13-nle-motilin on the electrical and mechanical activity of the isolated perfused canine stomach and duodenum. Gut 1976; 17:362-370.

occurring

at physiological

Motilin-induced

thoroughly

state.

the common

stomach.

motilin

innervation.

gic neurons

may activate

that regulates

1976;

7. Fox-Threlkeld JET, Manaka H, Manaka Y, Cipris S, Woskowska Z,

study had simigastric

in the resting

suggest that motilin

J Gastroenterol

contractions.

occurring

waves induced

to those

findings

Stand

activity recorded from the isolated, perfused canine stomach: the effects of some G.I. polypeptides. In: Daniel EE, ed. Proceedings of the International Symposium of Gastrointestinal Motility. 4th ed. Vancouver, Canada: Mitchell, 1974:233-242.

used in the present

on motilin-induced

pressure.

431

11:75-79. 5. ltoh Z. Effect on GI motility in dogs. In: ltoh Z, ed. Motilin. New York: Academic, 1990: 133- 153. 6. Hirning LD, Burks TF. Neurogenic mechanism of action of motilin in the canine isolated small intestine ex vivo. Eur J Pharmacol

tions. lar effects on spontaneously

sphincter

CONTRACTIONS

as a

18.

are in-

the role of a, re-

are needed.

Ref ecences

19. 20.

in the genetically obese-diabetic mouse (db/db). Diabetes 198 1;30:2 1 l-2 18. ltoh Z, Takeuchi S, Aizawa I, Mori K, Taminato T, Seino Y, lmura H, Yanaihara N. Changes in plasma motilin concentration and gastrointestinal contractile activity in conscious dogs. Am J Dig Dis 1978;23:929-935. Hall KE, Greenberg GR, El-Sharkawy TY, Diamant NE. Relationship between porcine motilin-induced migrating motor complexlike activity, vagal integrity, and endogenous motilin release in dogs. Gastroenterology 1984;87:76-85. Brown JC, Johnson CP, Magee DF. Effect ofduodenal alkalization on gastnc motility. Gastroenterology 1966;50:333-339. Thomas PA, Kelly KA, Go VLW. Does motilin regulate canine interdigestive gastric motility. Am J Dig Dis 1979;24:577-582. Van Lier Ribbink JA, Sarr MG, Tanaka M. Neural isolation of the entire canine stomach in VIVO: effects on motility. Am J Physiol 1989;257:G30-G40.

21. Gleysteen JJ, Sarna SK, Myrvik AL. Canine cyclic motor activity of Strunz U, Domschke W, Mitznegg P, Domschke S, Schubert E, WUnsch E, Jaeger E, Demling L. Analysis of the motor effects of 13-norieucine motilin on the rabbit, guinea pig, rat, and human alimentary tract in vitro. Gastroenterology 1975;68: 1485- 1495. LOdtke FE, Moller H, Golenhofen K. Direct effect of motilin on isolated smooth muscle from various regions of the human stomach. Eur J Physiol 1989;414:558-563. Segawa T, Nakano M, Kai Y, Kawatani H, Yajima H. Effect of synthetic motilin and related polypeptides on contraction of gastrointestinal smooth muscle. J Pharm Pharmacol 1976;28:650651. Lux G, Rosch W, Domschke S, Domschke W, WOnsch E, Jaeger E, Demling L. Intravenous 13-nle-motilin increases the human

stomach and small bowel: the vagus is not the governor. Gastroenterology 1985;88: 1926- 193 1.

22. Peeters T, Matthijs G, Depoortere I, Cachet T, Hoogmartens J, Vantrappen G. Erythromycin is a motilin receptor agonist. Am J Physiol 1989;257:G470-G474. 23. Otterson MF, Sarna SK. Gastrointestinal motor effects of erythromycin. Am J Physiol 1990;259:G355-G363. 24. Bockaert J, Fozard JR, Dumuis A, Clarke DE. The 5-HT, receptor: a place in the sun. Trends Pharmacol Sci, 1992; 13: 14 1- 145. 25. ltoh Z, Mizumoto A, lwanaga Y, Yoshida N, Torii K, Wakabayashi K. Involvement of 5-hydroxyttyptamine 3 receptors in regulation of interdigestive gastric contractions by motilin in the dog. Gastroenterology 199 1; 100: l-8.

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26. Andrews PLR, Bingham S. Adaptation of the mechanisms controlling gastric motility following chronic vagotomy in the ferret. Exp Physiol 1990;75:8 1 l-825. 27. Altaparmakov I, Wienbeck M. Alpha-adrenergic control of the interdigestive migrating complex (IDEMC). In: Labo G, Bortolotti M, eds. Gastrointestinal motility. Verona, Italy: Cortina International, 1983:3-7. 28. Holle GE, Milenov K, Forth W. Adrenergic control of interdigestive and digestive motility via the pyloric region. J Gastrointest Motil

1991;3:131-137. 29. Ormsbee Ill HS, Telford GL, Mason R. Required neural involvement in control of canine migrating motor complex. Am J Physiol 1979;237:E45 1-E456. 30. ECSharkawy TY, Markus H, Diamant NE. Neural control of the intestinal migrating myoelectric complex. A pharmacological analysis. Can J Physiol Pharmacol 1982;60:794-804. 31. Lambert GA, Lang WJ, Friedman E, Meller E. Pharmacological and biochemical properties of isomeric yohimbine alkaloids. EurJ Pharmacol 1978;49:39-48.

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Weiner N. Drugs that inhibit adrenergic nerves and block adrenergic receptors, I. a-Adrenergic blocking agents. In: Goodman Gil-

man A, Goodman LS, Gilman A, eds. The pharmacological basis of therapeutics. 6th ed. New York: Macmillan, 178-188. 33. Weiner N. Drugs that inhibit adrenergic nerves and block adrenergic receptors, II. 8-Adrenergic blocking agents. In: Goodman Gilman A, Goodman LS, Gilman A, eds. The pharmacological basis of therapeutics, 6th ed. New York: Macmillan Publishing, 188197. 34. Scriabine A, Torchiana L, Stavorski JM, Ludden CT, Minsker DH, Stone CA. Some cardiovascular effects of timolol: a new 8-adrenergic blocking agent. Arch Int Pharmacodyn 1973;205:76-93.

Received October 13, 1992. Accepted March 16, 1993. Address requests for reprints to: Zen Itoh, M.D., Gastrointestinal Laboratories, Institute of Endocrinology, Gunma University, Maebashi 371, Japan. The authors thank Fumie Mlzusawa for her technical assistance.