Alterations in spontaneous contractions in vitro after
repeated inflammation of rat distal colon
Carol
Bossone1,
Jeanette M.
Hosseini1,
Victor
Piñeiro-Carrero2, and
Terez
Shea-Donohue1,3
Departments of 1 Physiology, 2 Pediatrics, and
3 Medicine, Uniformed Services University of the Health
Sciences, Bethesda, Maryland 20814-4799
 |
ABSTRACT |
In inflammatory bowel disease,
smooth muscle function reportedly varies with disease duration. The aim
of these studies was to determine changes in the control of spontaneous
contractions in a model of experimental colitis that included
reinflammation of the healed area. The amplitude and frequency of
spontaneous contractions in circular smooth muscle were determined
after intrarectal administration of trinitrobenzenesulfonic acid in rat
distal colon. With the use of a novel paradigm, rats were studied
4 h (acute) or 28 days (healed) after the initial inflammation. At
28 days, rats were studied 4 h after a second inflammation
(reinflamed) of the colon. Colitis induced transient increases in the
amplitude of spontaneous contractions coincident with a loss of nitric
oxide synthase activity. The frequency of contractions was controlled by constitutive nitric oxide in controls. Frequency was increased in
healed and reinflamed colon and was associated with a shift in the
dominance of neural constitutive nitric oxide synthase control to that
of inducible nitric oxide synthase (iNOS). The initial colitis induced
a remodeling of the neural control of spontaneous contractions
reflecting changes in their regulation by constitutive nitric oxide
synthase and iNOS.
inflammation; colitis; rat; nitric oxide; smooth muscle; enteric
nerves
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INTRODUCTION |
ULCERATIVE COLITIS
and Crohn's disease are two chronic idiopathic diseases collectively
known as inflammatory bowel disease (IBD). These disorders are
characterized by prominent intestinal inflammation. Crohn's disease
may affect any part of the gastrointestinal tract, while the
inflammation in ulcerative colitis is restricted to the colon. The
etiologies of these disorders are unclear, but prominent clinical
features are diarrhea and abdominal cramping (17, 18). IBD
is further characterized by periods of quiescence during which
spontaneous relapse or acute reinflammation may occur. Early in the
disease, the mucosa may be indistinguishable from that in healthy
subjects during the inactive stage. Exacerbation of the disease occurs
during the cycles of remission and relapse, and, in more advanced
disease, the mucosa may be atrophic with a persistent diffuse
inflammation. After healing of the affected area, clinical symptoms
often reappear during acute relapse.
A major limitation in understanding the etiology of IBD is that few
animals spontaneously develop colitis. Research into the pathogenesis
of IBD has made use of several established animal models, particularly
the hapten 2,4,6-trinitrobenzenesulfonic acid (TNBS) in ethanol
(8, 15, 31, 34). This agent produces an acute inflammation
that progresses over several weeks to a chronic stage that is
morphologically similar to Crohn's disease. Typically, mucosal injury
and polymorphonuclear cell infiltration are observed within 2 h
after exposure to TNBS-ethanol (34). The lymphocytic
infiltration characteristic of chronic inflammation is evident at
48 h and evolves over several weeks (15, 34). However, experimental models of inflammation have not specifically investigated the changes that may occur after acute relapse that arguably may have more relevance to clinical disease. To address this
issue, we have modified an established animal model to evaluate changes
in the response of smooth muscle to an initial inflammation of the
distal colon followed by a period of recovery before reinflammation of
the healed area.
It is well recognized that inflammation is associated with alterations
in mucosal and motor function in both small intestine and colon
(8, 11, 12, 14, 16-18, 21, 22, 25, 26, 28, 30). In
addition, there is evidence suggesting that colonic motility varies
with disease activity (8, 11). As inflammation progresses,
there are changes in the profile of inflammatory/immune cells and
associated mediators that may directly or indirectly affect smooth
muscle contractility. Early clinical studies report both hypermotility
(26) and hypomotility (11) in ulcerative colitis patients. Moreover, ulcerative colitis patients exhibit changes
in the frequency of spontaneous contractions that vary with the
duration of their disease (11). There are few studies of
spontaneous contractions in the colon in experimental models of
inflammation. However, in acetic acid-induced ileitis in dogs, the
number of spontaneous phasic contractions was reduced in the first
week, and this correlated well with the decreased contractility of
smooth muscle strips in vitro (21).
Colonic circular smooth muscle exhibits spontaneous phasic contractions
that are subservient to the slow wave frequency. Both excitatory and
inhibitory neurotransmitters are important in the regulation of colonic
smooth muscle contraction. Previous studies in our laboratory suggested
a role for inhibitory neurotransmitters in controlling smooth muscle
contraction (8, 11). Nitric oxide (NO) has been identified
as an important inhibitory neurotransmitter or neuromodulator in the
enteric nervous system (1, 2, 9, 10, 32). Morphological
studies of canine colon suggest that NO is also a critical intermediary
in the communication between interstitial cells of Cajal (ICC), enteric
inhibitory nerves, and smooth muscle in the generation of spontaneous
contractions (12). Recently, impaired nitric oxide
synthase (NOS) activity in nerves was implicated in the reduced ability
of smooth muscle to relax in colitis induced by dextran sulfate sodium
in rats (14). Thus the aim of the proposed studies was to
determine the changes in the nitrergic control of spontaneous
contractions in an animal model of experimental colitis in the
following three different stages: acute inflammation, healed mucosa,
and acute reinflammation of the healed area.
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MATERIAL AND METHODS |
Induction of Inflammation
Experiments and animal care were conducted in compliance with
guidelines outlined by the Guide for the Care and Use of Laboratory Animals (Institute of Animal Research, National Research Council). Male
Sprague-Dawley rats (200-400 g; Taconic Farms) were assigned at
random to one of the following four treatment groups: control, acute,
healed, or reinflamed. After an overnight fast (water ad libitum), rats
were anesthetized with 8 mg/kg xylazine (Miles, Shawnee Mission, KS) in
combination with 40 mg/kg ketamine (Fort Dodge Laboratories, Fort
Dodge, IA) intramuscularly. The control group received 1 ml saline
intrarectally, whereas acute, healed, and reinflamed animals were given
100 mg/kg TNBS (Sigma, St. Louis, MO) in a 50% ethanol solution
intrarectally. Four hours later, control and acute animals were
reanesthetized for surgical removal of a 4- to 5-cm section of distal
colon (midtransverse to distal portion). Healed and reinflamed animals
were allowed to recover and were monitored for 4 wk. After four weeks,
rats were reanesthetized and reinjected intrarectally with either 1 ml
saline (healed) or 100 mg/ml TNBS in 50% ethanol (reinflamed), and
tissue was harvested 4 h later as performed previously for control
and acute animals. All rats were killed with an overdose of
pentobarbital sodium (10 mg/kg).
Histology
Full-thickness sections of distal colon from each animal were
fixed in 10% neutral buffered formalin, embedded in paraffin, sectioned, and stained with either hematoxylin and eosin (H & E) or
Giemsa. With the use of an ocular micrometer (Olympus; Olympus Optical,
Tokyo, Japan), the thicknesses of muscularis externa, circular
muscularis externa, muscularis mucosae, and submucosa were
measured on H & E-stained sections with a ×20 objective on a light
microscope. At least three measurements were taken, and values were
averaged. An investigator who was unaware of the treatment given graded
the sections. A score of 1-5 was determined by giving one point
for each of the following features: 1) mucosal sloughing, 2) vasodilatation, 3) submucosal edema,
4) hemorrhage, and 5) increased thickness of the
muscle layer. A minimum of seven slides was evaluated in each treatment
group. The number and distribution of inflammatory cells were evaluated
in three to eight well-oriented areas in Giemsa-stained sections. In
addition, mucosa-free sections of distal colon from each group were
fixed in 4% paraformaldehyde in PBS for visualizing NADPH diaphorase
as an index of NOS activity using the method of Shuttleworth et al.
(23). For each section, the number of stained neurons was
counted, and the section was photographed by an investigator blinded to
the treatment group.
In Vitro Smooth Muscle Contractions
With the use of a double-blade scalpel, 2-mm-wide mucosa-free
segments of the distal colon were cut, mounted in organ baths in their
circular axis, and maintained in an oxygenated (95% O2-5% CO2) Krebs solution at 37°C throughout the experiment.
Krebs solution contained (in mM) 118.5 NaCl, 4.75 KCl, 2.54 CaCl2, 1.19 MgSO4, 25 NaHCO3, 1.19 NaH2PO4, and 11.0 dextrose. The length of
maximal active tension (Lo) was determined using
ACh (10
4 M). All experiments were performed at
Lo.
Muscle strips were allowed to equilibrate for 20-30 min before
addition of the ganglionic blocker hexamethonium (100 µM), the NOS
inhibitor NG-nitro-L-arginine
(L-NNA, 10 µM), the inducible NOS (iNOS) inhibitor aminoguanidine (10 µM), or the sodium channel blocker TTX (1 µM). Aminoguanidine is reported to be a selective, but incomplete, inhibitor
of iNOS at this concentration (33). TTX was prepared in a
citrate buffer (50 mM citric acid and 48 mM
NaH2PO4) and chilled. All chemicals were
obtained from Sigma. All antagonists were added to the muscle baths 30 min before measurements. Fresh oxygenated Krebs solution was changed in
the baths every 10 min, and the drugs were added back after each
washing so that the tissue was exposed to the drug for a total of 30 min. Hexamethonium and aminoguanidine were dissolved in distilled water
and chilled. L-NNA was dissolved in distilled water and
maintained at 37°C. Vehicle-treated strips received the same volume
and identical administration times of the appropriate dissolving
solvent for each antagonist.
Data Analysis
The amplitude (mN/cm2), frequency (no. of
contractions/10 min), and duration (s) of the spontaneous contractions
were measured (model 79E polygraph; Grass, Quincy, MA) after the
addition of vehicle, L-NNA, hexamethonium, TTX, or
aminoguanidine. Tension was determined using the method of Percy et al.
(16) and was defined as
where mass was corrected for water content by multiplying the
wet weight by 1.056 (the muscle density). The mass of muscle was
corrected for the circular muscle component of the muscularis externa
by multiplying by 0.726 (the measured percent of circular muscle). Four
strips of muscle were obtained from each animal, and values for each
parameter (e.g., hexamethonium) represent the means of strips taken
from six different rats. Each strip was incubated with only one
antagonist (e.g., hexamethonium). Measurements from each strip were
averaged, and data are expressed as means ± SE. There were no
differences among individual responses in vehicle alone, so only the
water vehicle is presented (Figs. 1-7 and Tables 1 and 2).
Differences in morphometric parameters among groups were analyzed by
one-way ANOVA followed by the t-test using the Bonferoni
correction (Prism Graphpad, Philadelphia, PA). Differences among groups
in concentration-response curves were analyzed by multiple ANOVA using
the Systat 5.2 program (Systat) followed by post hoc analysis for
differences between individual means. For analysis of differences in
NADPH diaphorase staining, unlabeled photomicrographs were arranged in
order of staining intensity and were analyzed using the Kruskal-Wallis
test, a nonparametric method of evaluating more than two groups. A
representative section from each group was selected for inclusion in
this report.

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Fig. 1.
Representative photomicrographs of Giemsa-stained
sections (5 µm) of the rat distal colon 4 h after intrarectal
administration of saline (A) or 2,4,6-trinitrobenzene
sulfonic acid (TNBS; B) or 4 wk and 4 h after initial
intrarectal administration of TNBS followed by saline (C) or
TNBS (D).
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Fig. 2.
Representative photomicrographs of NADPH
diaphorase-stained sections (5 µm) of the rat distal colon 4 h
after intrarectal administration of saline (A) or TNBS
(B) or 4 wk and 4 h after initial intrarectal
administration of TNBS followed by saline (C) or TNBS
(D).
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Fig. 3.
Changes in the amplitude of spontaneous phasic
contractions 4 h after intrarectal administration of saline
(control) or TNBS (acute) vs. 4 wk and 4 h after initial TNBS
followed by saline-treated healed tissue (healed) or TNBS-induced
reinflammation (reinflamed) *P < 0.05 vs. control.
P < 0.05 vs. healed.
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Fig. 4.
Examples of mechanical activity in circular smooth muscle
taken from rat distal colon 4 h after intrarectal administration
of saline (A) or TNBS (B) or 4 wk and 4 h
after initial TNBS followed by saline (C) or TNBS
reinflammation (D) in distal colon.
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Fig. 5.
Changes in the amplitude of spontaneous phasic contractions in the
presence of vehicle (VEH), hexamethonium (HEX), TTX , NG-nitro-L-arginine
(L-NNA), or aminoguanidine (AG) for control (4 h
postsaline), acute (4 h post-TNBS), healed (4 wk post-TNBS + 4 h postsaline), or reinflamed (4 wk post-TNBS + 4 h
post-TNBS) tissue. Tissue was incubated with antagonists for 30 min
before measurements. *P < 0.05 and **P < 0.01 vs. control. P < 0.05 vs. respective
vehicle within group.
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Fig. 6.
Changes in the frequency of spontaneous phasic
contractions 4 h after intrarectal administration of saline
(control) or TNBS (acute) vs. 4 wk and 4 h after initial TNBS
followed by saline (healed) or TNBS-induced reinflammation
(reinflamed). *P < 0.05 vs. control.
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Fig. 7.
Changes in the frequency of spontaneous phasic contractions in the
presence of vehicle, hexamethonium, TTX, L-NNA, or
aminoguanidine for control (4 h postsaline), acute (4 h post-TNBS),
healed (4 wk post-TNBS + 4 h postsaline), or reinflamed (4 wk
post-TNBS + 4 h) tissue. Tissue was incubated with
antagonists for 30 min before measurements. *P < 0.05 vs. control. P < 0.05 vs. respective
vehicle within group.
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Table 1.
Changes in colonic smooth muscle morphology (muscle thickness), PMN
count, and mucosal injury scoring during acute colitis followed by
healing and reinflammation of the affected area
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RESULTS |
Histology
Histological findings are presented in Table
1, and representative photomicrographs of
H & E-stained sections from all four treatment groups are
shown in Fig. 1, A-D.
The microscopic appearance of the colonic epithelium after the first
acute inflammation showed significant neutrophilic infiltration in the
crypts and mucosal injury featuring vascular congestion, submucosal
edema, and mucosal sloughing. The muscularis propria was unchanged at
this time. After 4 wk, the mucosa was healed but could be distinguished
from controls by more prominent goblet cells, distorted crypts, and the
presence of neutrophils and lymphoid infiltrates. During acute reinflammation, there was significantly greater tissue damage and
neutrophilic infiltration compared with acute inflammation as well as
the presence of lymphocytic-type infiltrates that were not observed in
the acute group. The intensity of NADPH diaphorase staining of
myenteric plexus and enteric nerves was dramatically less in acute and
reinflamed tissue than in controls. The intensity of staining in healed
tissue was less than in controls but was still present. There were no
differences in the number of neurons present (control, 11.5 ± 1.5; acute, 8.0 ± 2.1; healed 12.33 ± 1.6; reinflamed,
11.5 ± 1.5), only in the intensity of the staining. Representative examples of NOS-stained photomicrographs are shown in
Fig. 2.
Spontaneous Smooth Muscle Contractions
Amplitude.
The colonic smooth muscle from the saline-treated group exhibited
spontaneous contractions that were nifedipine sensitive. The amplitude
of these contractions was increased significantly by acute
inflammation, returned to control values in the healed group, and was
elevated significantly again upon reinflammation (Figs.
3 and 4,
A-D). To further explore the inflammation-induced alterations in spontaneous contractions, amplitude was compared in the
presence and absence of the nonspecific NOS inhibitor
L-NNA, the selective inhibitor of iNOS aminoguanidine
(27), the sodium channel blocker TTX, or the ganglionic
blocker hexamethonium (Fig. 5,
A-D). In both control and healed tissue, the amplitude was elevated by L-NNA and TTX, suggesting that the amplitude of
spontaneous contractions is subject to tonic inhibitory control by
nitrergic and other nerves. In contrast, contractile amplitude was
unaltered by hexamethonium and aminoguanidine, showing a lack of
control by ganglionic neurons or inducible NO in controls. In acute
inflammation, the significantly enhanced amplitude was not elevated
further by any treatment, indicating a loss of nitrergic and other
neural control. The effect of the various antagonists on spontaneous contractions in reinflamed tissue was nearly identical to that in the
acute group; however, amplitude was elevated further by TTX, indicating
a loss of nitergic but not other neural control in the reinflamed
group. Thus, during the initial inflammation, there is a loss of both
nitrergic and other neural control of amplitude that was restored in
the healed group. In contrast, in response to a second inflammation of
this healed area, only the nitrergic neural control was lost.
Duration.
In controls, the duration of spontaneous contractions was unchanged in
the presence of any antagonist tested (Table
2). Compared with controls, the duration
of contractions was lengthened significantly by acute inflammation
[Fig. 3 (amplitude) and Fig. 4, A vs. B (duration)] and was prolonged further in the presence of TTX (Table 2). Duration returned to control values in the healed stage, but,
unlike control, duration was extended in the presence of L-NNA, TTX, or hexamethonium. Compared with controls, the
duration of spontaneous contractions was enhanced again upon
reinflammation and was lengthened further by TTX and L-NNA.
Frequency.
When compared with controls, acute inflammation had no effect on the
frequency of spontaneous contractions (Fig.
6 and Fig. 4, A vs.
B). In contrast, there was a marked increase in frequency in
both the healed and reinflamed groups (Fig. 6 and Fig. 4, C and D). In controls, frequency was significantly elevated
only in the presence of L-NNA (Fig.
7, A-D), indicating a tonic
inhibitory control by nitrergic nerves. In contrast, in the acute
group, frequency was insensitive to any antagonist, showing a loss of this nitrergic influence. In the healed group, frequency was reduced significantly in the presence of hexamethonium and aminoguanidine but
not TTX or L-NNA, while in the reinflamed group, frequency was reduced to control values by all antagonists tested. These data
indicate that the initial inflammation induced a shift in control of
the frequency of spontaneous contractions from nitrergic nerves to a
pathway that involves myenteric neurons and inducible NO.
 |
DISCUSSION |
IBD patients generally experience periods of active disease
followed by resolution of the mucosal injury and healing. This may be
followed by a period of inactivity or quiescence that is interrupted by
an acute relapse, the most frequent symptom of which is diarrhea.
Repetition of this cycle often leads to exacerbation of the disease. In
the present study, contractility of distal colonic circular smooth
muscle was assessed in groups of rats 4 h after TNBS-induced
inflammation of the distal colon, 4 wk after the initial inflammation
during a period of quiescence, or 4 h after reinflammation of the
affected area. The microscopic appearance of the distal colon taken
from the acute and reinflamed groups featured mucosal damage,
submucosal edema, and vasocongestion and/or hemorrhage. However, the
initial acute inflammation had a significant neutrophil infiltration,
whereas inflammatory cells in the reinflamed group were neutrophils as
well as lymphocytes and monocytes. These lymphoid aggregates are a
feature of more chronic disease in this model (6, 15, 34).
More importantly, there were alterations in the neural control of both
the amplitude and frequency of spontaneous contractions consistent with
an inflammation-induced remodeling of enteric nerves.
Abnormal gut motility is a common feature of IBD (3, 17, 18, 26,
28, 30). Previous studies showed that inflammation alters
circular smooth muscle contractile properties and responses to
neurotransmitters or nerve stimulation (5, 15, 24). In
healthy colon, circular smooth muscle exhibits nifedipine-sensitive rhythmic spontaneous contractions in vivo and in vitro that are electrically coupled to slow waves (9, 10). NO plays an
important role in the regulation of the amplitude of contractions in
the colon by controlling the inherently excitable smooth muscle
syncytium (9, 10, 13, 32). In addition, there are
reportedly fewer NOS-containing neurons in the distal than in the
proximal colon, an observation that is consistent with its ability to
generate large-amplitude propulsive contractions (29). In
the present study, the amplitude of spontaneous contractions was
elevated in healthy controls by either TTX or the nonspecific NOS
inhibitor L-NNA. The lack of an effect on amplitude of
contractions of the iNOS inhibitor aminoguanidine supports previous
reports that phasic contractile activity is suppressed continuously by
the release of constitutive NO from nerves (9, 29). The
mechanical data and immunohistochemical localization of NADPH
diaphorase staining in nerves and neurons in the rat colonic muscularis
externa in the present study are consistent with earlier findings in
rodents (2, 4, 14), dogs (10, 22), and humans
(9, 24). The amplitude of spontaneous contractions was
unaffected by hexamethonium, indicating that the tonic inhibitory
neural control is independent of nicotinic ganglionic neurotransmission.
Acute inflammation of the colon significantly elevated the amplitude
and duration of spontaneous contractions but had no effect on the
frequency. Previous reports showed that smooth muscle contractility is
decreased at 3-7 days after induction of colitis (6, 11, 15). Frequency was also unaffected in the first week after
induction of colitis (12). Long-duration slow waves were
associated with high-amplitude spontaneous contractions in healthy
canine colon (10), suggesting that the duration and
amplitude of phasic contractions in this study are electrically coupled
to the duration of slow waves. The increased amplitude of contractions
in the presence of L-NNA or TTX observed in control tissue
was absent in acute inflammation, suggesting a loss of neural NO
control. This is concurrent with the reduction in NADPH diaphorase
staining in the distal colon of these rats, indicating a likely
reduction in constitutive NOS (cNOS) activity. The specificity of NADPH diaphorase staining for neuronal NOS (nNOS) has been confirmed by
others showing that NOS activity and NADPH diaphorase copurify to
homogeneity and that both activities could be immunoprecipitated with
an antibody recognizing neuronal NADPH diaphorase (7). Recent studies demonstrated that the impaired ability to relax smooth
muscle was associated with a reduction in nNOS immunoreactivity (14), comparable to the reduction in NADPH diaphorase
staining observed in the present study. Similarly, they also observed
reduced nNOS without a reduction in the number of myenteric neurons,
indicating that the effects on contractility are not due to a general
decrement in the population of neurons (14). These data
suggest that loss of NO control in acute inflammation in the present
study leads to an elevation in contractile amplitude. This may be
linked electrically to an overall depolarization of the resting
membrane potential and/or an increase in the frequency of long-duration
slow waves.
An alternative explanation for the increased contraction could be
explained by changes in excitatory neurotransmitters such as ACh. We
showed previously that acute inflammation increased the responses to
ACh and substance P, an effect attributed to a loss of neural
inhibition rather than an increase in excitation (8). In
addition, these studies showed that colitis suppressed the neural
inhibition derived, in part, from ACh acting at nicotinic receptors in
the myenteric plexus (8). Thus it is likely that reduced
inhibitory input resulting from a decrease in NOS activity in enteric
nerves underlies the enhanced contractile amplitude observed in the
present study.
Regulation of spontaneous contractile amplitude in healed tissue was
nearly identical to that in controls, and the increased amplitude in
response to reinflammation of the affected area was similar to that
observed in acute colitis. Thus it appears that both the initial
inflammation and recurrence of active disease induce a transient
increase in contractile amplitude and duration. This is coincident with
a loss of neural cNOS activity as evidenced by the reduction in NADPH
diaphorase staining in the nerves in this tissue rather than to a
decrease in the number of neurons.
In contrast to amplitude, the frequency of spontaneous contractions was
not altered by the initial inflammation. Instead, frequency was
elevated significantly at 4 wk after TNBS in both the healed and
reinflamed colon, indicating that the initial colitis caused
long-lasting alterations in the frequency of phasic contractions. In
vivo studies in human colon have shown that the slow wave rhythm may be
elevated in patients with ulcerative colitis (11, 26). NO
is considered to be an important factor in the control of pacemaker activity. The results of the current study support a role for iNOS in
the inflammation-induced alterations in slow wave frequency. Inflammation is known to enhance iNOS activity, resulting in an overproduction of NO. The origin of this NO may be from a number of
sources, including macrophages, epithelial cells, or the smooth muscle
cells themselves (19, 24). In the present study, the rate
of spontaneous contractions in control animals was elevated only in the
presence of L-NNA, suggesting a role for NO in the control
of basal frequency. These data support previous reports implicating NO
in the regulation of ICC function (20). In
contrast, in healed and reinflamed tissue, the increased frequency was
reduced by aminoguanidine but not by L-NNA. Thus the
initial inflammation induced a remodeling of the control of contractile
frequency from cNOS-derived NO to iNOS-derived NO. The ability of
hexamethonium to reduce frequency in healed and reinflamed tissue
indicated the acquisition of a ganglionic regulation of frequency in colitis.
In conclusion, we have modified an experimental model of inflammation
to establish a novel approach to the effects of colitis on smooth
muscle function. The morphological appearance of healed and reinflamed
colon has similarities to patients with quiescent and active IBD. In
vitro studies of smooth muscle demonstrate that the smooth muscle
activity after an initial inflammation differs dramatically from the
response after reinflammation of the healed area. Both acute and
reinflammation colitis induce a transient increase in the amplitude of
spontaneous phasic contractions that can be attributed to a loss of
inhibitory nitrergic control. In addition, the initial inflammation
induces a long-lasting alteration in the frequency of spontaneous
contractions that suggests a remodeling of the interactions between
smooth muscle and nerves. It is proposed that changes in cNOS
affect contractile amplitude, although there is a shift in the control
of frequency from cNOS to iNOS.
 |
ACKNOWLEDGEMENTS |
The opinions contained herein are the private ones of the authors
and are not to be construed as official policy or reflecting the views
of the Department of Defense.
 |
FOOTNOTES |
These studies were supported by a grant from the Crohn's and Colitis
Foundation of America.
Address for reprint requests and other correspondence: T. Shea-Donohue, Dept. of Medicine, Uniformed Services Univ. of the Health
Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814-4799 (E-mail:
tshea{at}usuhs.mil).
The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement"
in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 17 May 2000; accepted in final form 1 December 2000.
 |
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