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Chuan-Yong
Liu, Jing-Zhang Liu, Jian-Hua Zhou, Han-Ru Wang, Zi-Ying Li, Ai-Jun Li,
Ke-Jing Liu, Department of Physiology,
Shandong Medical University, Jinan 250012, Shandong Province, China.
Chuan-Yong Liu, male, born on 1969-05-29
in Dezhou City, Shandong Province, graduated from Shandong Medical
University as a postgraduate in 1995, Lecturer of Department of
Physiology, Shandong Medical University, having two papers
published.
Presented at the First International Conference on Gastrointestinal
Electric Activity and Motility, Beijing, China, 24-26
September,1996.
Supported by the Natural Science Foundation of Shangdong
Province (Y95c1032).
Correspondence to: Chuan-Yong Liu, Department of Physiology,
Shandong Medical University, Jinan 250012,
Shandong Province, China.
Telephone: +86-531-2942037 ext 671 or 628
Received: 1997-12-05 Revised: 1997-12-30
Subject
headings: gallbladder; vagus nerve;
dorsal vagal complex; thyrotropin releasing hormone; cholinergic M
receptors; rabbits
Liu CY, Liu JZ, Zhou JH, Wang HR, Li ZY, Li AJ, Liu KJ.TRH
microinjection into DVC enhances motility of rabbits gallbladder via
vagus nerve.World J Gastroentero,1998;4(2):162-164
Abstract
AIM: To investigate the effects of TRH in DVC on motility of
the gallbladder in rabbits.
METHODS: fter fasted for 15h-18h, rabbits were anesthetized
with urethane (1.0g/kg). Gallbladder pressure (GP) was measured by a
frog bladder perfused with normal saline.
RESULTS: After microinjection of TRH (8.8nmol,1μl) into
DVC, GP was raised and the frequency of phasic contraction of
gallbladder (FPCGB) increased. All the doses of TRH (0.13, 0.25,
0.50, 0.80, 1.30nmol, 1μl) injected into DVC could excite the
motility of gallblader. As the dose of TRH was enlarged, the
amplitude and duration of the reaction increased. Effects of TRH in
DVC on motility of the gallbladder could be completely abolished by
atropine (0.2mg/g, i.v.) or vagotomy, but could not be inhibited by
phentolamine iv (1.5mg/g) or propranolol iv (1.5mg/g)or by
transecting the spinal cord.
CONCLUSION: Thyrotropin-releasing hormone in DVC can excite
motility of gallbladder. This effect was mediated by vagus nerves
and peripheral M receptor. Its physiological significance may be
related to maintaining the phasic contraction of gallbladder in
interdigestive period.
INTRODUCTION
Our previous studies indicated that the dorsal vagal complex (DVC)
might play an important role in regulating motility of extrahepatic
biliary tree［1］,
but we do not know which neurotransmitter mediates this effect.
Thyrotropin-releasing
hormone (TRH) is one of important brain gut peptides［2］.
There is a high density of TRH-immunoreactive nerve terminals in DVC［3］.
Injecting TRH into DVC could excite the motility and secretion of
stomach ［2］.
However, there is no report about TRH in DVC on the motility of
extrahepatic biliary tree. In this study, TRH was injected into DVC
of anesthetized rabbits, and then the effect on mean gallbladder
pressure (GP) and frequency of phasic contraction of gallbladder (FPCGB)
were observed, and the peripheral route of the effect of TRH was
also investigated.
MATERIALS AND METHODS
Animal preparation
The experiments were conducted in 38 rabbits weighing
2.0kg-2.5kg. Fasted for15h-18h, but allowed to drink water, the
rabbits were anesthetized with urethane (1.0g/k, iv.). A cannula was
inserted into the trachea. Unilateral femoral artery was
catheterized for measurement of blood pressure. The rectal
temperature was maintained at 37℃-385℃.
Measurement of GP
A frog bladder filled with saline was placed in gallbladder and
connected to a transducer (TP-200T) by a catheter. The blood
pressure and GP were recorded simultaneously by a polygraph
(RM-6000, NIHON KOHDEN).
Microinjection of TRH
The animal′s
head was fixed in a stereotaxis (I-C model, JIANG WANG, China).
According to the Messen′s
methods, a stainless steel guide tube (0.5mm in outer diameter)
containing a needle was inserted into DVC (rostral from obex
0.5mm-1.0mm, left or right from midline 0.7mm-1.2mm, depth from the
surface 0.5mm-1.2mm). Normal saline or TRH solution(1μl) was
injected into DVC by a microsyringe connected to a cannula (0.3mm in
outer diameter).
Statistical analysis
Before the following tests were made, the basal level of GP of each
animal was taken as control (i.e., basal GP as 0 kPa in place of
real level). GP increase during the test, was considered as positive
(+) value, while GP decrease was taken as negative (－).
Student′s
t test was used for the statistical analysis. All values were
mean±SD.
P＜0.05
was considered to be statistically significant.
RESULTS
Normal GP
In interdigestive period, two kinds of motion of gallbladder were
found, the tonic and phasic contractions. Tonic contraction, which
means continuous and weak contraction, could maintain GP at a stable
level (2.67×103±190Pa, n=8). Phasic contraction,
with a duration of 5-20s and frequency of
1-3 times per minute, raised GP by 60kPa-200kPa rhythmically (Figure
1a).
Microinjection of TRH into DVC
After TRH (0.8nmol,1μl) was microinjected into DVC, the
motility of gallbladder was enhanced. The effect occurred in 1min
after the injection, reached its peak in 10 minutes and returned to
normal within 20min-30min. At 5min after injection, GP increased by
167kPa
±29kPa (n=5, P＜0.02);
FPCGB increased from 1.14±0.26 to 2.28±0.26 per min (n=5, P＜0.034)
(Figures 1b, 2-3 ). However, after normal saline (1μl) injected
into DVC or TRH (0.8nmol, 1μl ) into the control position in
medulla (lateral 0.5mm-1.0mm to the DVC), the GP and FPCGB did not
change significantly.
Dose-response of TRH microinjected into DVC on the GP and
FPCGB
All the doses of TRH (0.13, 0.25, 0.50, 0.80, 1.30nmol, 1μl)
microinjected into DVC could excite the motility of gallbladder. As
the dose increased, the strength and duration of the effect of TRH
on GP and PCGB went up, with a significant dose response (Figures 4
and 5).
Peripheral route of the TRH effect on the motility of
gallbladder.
Ten minutes after the cervical vagotomy (n=5) or i.v.
injection of atropine (0.2g/kg,n=5), microinjection of TRH
(0.8nmol, 1μl ) could no longer excite the motility of
gallbladder. Within 30 minutes after the injection of TRH, the GP
and FPCGB had no
significant changes (Figure 1b, c). However, ten minutes after
transection of the spinal cord from T1 or i.v. injection of
phentolamine (1.5mg/kg)
or propranolol (1.5mg/kg), injection of TRH into DVC could also enha
nce the motility of gallbladder (Figure 1d, e, f).
Figure
1(PDF) The effects of TRH microinjected
into DVC on the GP. A. control; B. TRH (0.8nmol/1μl ); C. i.v.
atropi
ne (0.2mg/kg); D. vagotomy; E. i.v. phentolamine (1.5mg/kg)
; F. i.v. propranolol (1.5mg/kg) ; G. after transection of spinal
cord through T1; G.↓
(0.8nmol/1μl) .
Figure 2(PDF)
The effects
of microinjection of TRH (0
.8nmol/1μl) or NS on GP. * P ＜0.05
as compared with NS
Figure 3(PDF) The effect of
microinjection of TRH (0.8nmol/1μ1) or NS on the frequency of
phasic contraction of gallbladder (FPCGB). **P＜0.01,
*P＜0.05
as compared with NS
Figure 4(PDF)
Dose-response curve for TRH stimulation on GP after microinjection
into DVC.
Figure 5(PDF)
Dose-response curve for TRH stimulation on the number of phasic
contraction of GB (PCGB) after microinjection into DVC.
DISCUSSION
In this study, we found that TRH microinjection into DVC raised GP
and FPCGB. As an important brain gut peptide, TRH in DVC plays an
important role in regulating the function of gastrointestinal tract［2］.
We found for the first time that TRH microinjected into DVC excited
the motility of gallbladder in rabbits.
The
effects of TRH microinjected into DVC on the motility and secretion
of gut may be physiological. In DVC, there is a high density of TRH
immunoreactive nerve terminals which come from the nucleus raphe
pallidus and raphe obscurus
. Some of these terminals make synaptic contacts on the dendrities
of gastric vagal motoneurons［5］.
Multicolon TRH antibody injected into DVC can inhibit the gastric
acid secretion［6］.
Through
vagus nerve and peripheral cholinergic M receptors, TRH could excite
the gallbladder motility, but its physiological significance is
unknown. Bile evacuation occurrs during sham feeding, and is
abolished by vagotomy
［7］.
After vagotomy or gastrectomy, the incidence of gallstones increases［8,9］.
In this experiment, TRH in DVC raised GP and then facilitated the
bile evacuation. Thus TRH may be a possible candidate for the
transmitter in DVC mediating the cephalic bile output.
The
present experiment showed that there was rhythmic phasic contraction
of gallbladder in rabbits in the interdigestive period, which was
similar to that found in dogs［10］.
It was believed that this phasic contraction stirred the bile in
gallbladder and prevented gallstones forming in the interdigestive
period［11］.
Our experimental results also showed that TRH microinjected into DVC
enhanced the phasic contraction via vagus nerve. Thus TRH in DVC may
be regarded as an important neurotransmitter in mediating the phasic
contraction of gallbladder. Similar to Ura′s
data in dogs
［11］,
vagotomy almost inhibited the phasic contraction completely in our
study. It was suggested that the tonic excitation of vagus nerve
center may be important in maintaining this type of motion in the
interdigestive period. TRH may participate in this effect.
In
conclusion, we believed that TRH in DVC may play an important role
in regulat
ing the motility of gallbladder via vagal nerves and peripheral
cholinergic M re
ceptors, and may participate in cephalic gallbladder emptying during
ingestion and maintain the phasic contraction of gallbladder in the
interdigestive period.
ACKNOWLEDGEMENT We are grateful to Professor HE Zhu Li,
Director of the Department of English, Shandong Medical University,
for polishing the manuscript.
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