Cyclooxygenase-2 is expressed in bladder during fetal
development and stimulated by outlet obstruction
John M.
Park1,
Tianxin
Yang2,
Lois J.
Arend4,
Ann M.
Smart2,
Jurgen B.
Schnermann3, and
Josephine P.
Briggs2,3
1 Section of Urology,
Department of Surgery; 2 Division
of Nephrology, Department of Internal Medicine; and
3 Department of Physiology and
4 Department of
Pathology, University of Michigan Medical School, Ann Arbor,
Michigan 48109
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ABSTRACT |
Studies were undertaken to assess expression of inducible
cyclooxygenase (COX)-2 in bladder during fetal development and COX-1 and COX-2 expression after outlet obstruction. Bladder tissue or
bladder progenitor tissue was harvested from CD-1 murine embryos at
embryonic days 11.5 (E11.5),
E14.5,
E17.5,
E20.5 (newborn), and from adult.
Bladder obstruction was created in adult female mice by ligating the
urethra, and bladders were harvested after 3-24 h of obstruction.
Gene expression was assessed by semiquantitative reverse
transcription-polymerase chain reaction and Western blotting. COX-2 was
highly expressed at the early stages of bladder development and
declined progressively throughout gestation. In adult bladder, both
COX-1 and COX-2 were detectable at low levels under basal conditions.
An ~30-fold increase in COX-2 mRNA was seen after 24 h of
obstruction. In contrast, COX-1 did not change with obstruction. COX-2
mRNA levels peaked at 6 h of obstruction. In regional
bladder-distention models, COX-2 induction was confined to the area of
distention. Bladder outlet obstruction stimulates COX-2 expression
dramatically, reactivating a gene that is highly expressed during fetal
development.
genitourinary system; distention; stretch; prostaglandin; embryogenesis
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INTRODUCTION |
PROSTAGLANDINS (PGs) have been thought to play an
important role in lower urinary tract function (20, 28, 31). Although urinary PGs also originate from kidney and prostate, it is established that the bladder is an independent site of PG synthesis and that bladder PG synthesis is enhanced by stimuli such as distention and
inflammation (28). In both experimental animals (5, 21, 22) and human subjects (2, 3), PGs may modulate
micturition reflexes and may protect bladder epithelium (6, 29) in a fashion analogous to their cytoprotective effect on gastric mucosa (39).
One key enzymatic step of PG production is cyclooxygenase
(COX)-mediated conversion of arachidonic acid to prostaglandin
H2, the common PG precursor. COX
is the inhibitory target of aspirin and various nonsteroidal
anti-inflammatory drugs (38). It has recently been established that COX
exists in two distinct isoforms (8, 15) that are products of different
genes and subject to differential regulation. Although translation
products of both COX-1 and COX-2 genes are ~72 kDa and possess
comparable COX activity, they share only 59% homology in amino acid
sequence (35). COX-1, known as the constitutive isoform, is expressed
in many tissue sites under basal conditions and has generally been
assigned to various housekeeping functions, such as platelet
aggregation, regulation of renal transport function, and gastric
mucosal cytoprotection (4, 35). COX-2, on the other hand, is known as
an inducible isoform. It has a limited pattern of basal expression but
is rapidly induced by a number of mitogenic and hormonal stimuli (7). COX-2 is thought to play a role in inflammatory and proliferative responses (4, 35).
The present studies were performed to test the hypothesis that outlet
obstruction would alter the expression of either the COX-1 or COX-2
isoform. Both COX-1 and COX-2 transcripts were expressed at low levels
in adult bladder under basal conditions. Bladder wall distention
resulted in a marked and prompt stimulation of COX-2 expression at both
mRNA and protein levels, whereas COX-1 expression remained unchanged.
When regional distention was produced by banding the bladder, COX-2
stimulation was confined to the distended region of the bladder. To
test the hypothesis that genes activated by injury may represent
reactivation of gene pathways active during development, studies were
also performed to evaluate COX-2 expression during the early stages of
fetal bladder development.
 |
MATERIALS AND METHODS |
Dissection of fetal bladder tissues.
Murine gestation is typically 20-21 days, with the day of
conception being designated as embryonic day
0 (E0.0). The
developing bladder or its progenitor tissue was dissected from murine
CD-1 embryos at gestational ages E11.5,
E14.5,
E17.5,
E20.5 (newborn), and from adult
animals. After E14.5, the anatomic
configuration of the developing bladder has assumed that of mature
animals. At E11.5, however, the true bladder does not yet exist; the nephric ducts and developing ureteric bud empty into the cloaca, which is the bladder progenitor (36). In
E11.5 fetuses, therefore, the nephric
ducts and ureteric buds were first identified as anatomic landmarks,
and the portion of the cloaca into which these structures drained was
identified under the dissection microscope using dark-field
illumination. A segment of this tissue, ~1-2
mm2, at the site of the nephric
duct orifices was dissected free. At later gestational stages, 1- to
2-mm2 full-thickness bladder
tissue was harvested from each fetus. Three separate litters were
analyzed for each gestational time point.
Bladder outlet obstruction. Adult
female CD-1 mice weighing 30-40 g were anesthetized with an
intraperitoneal ketamine (0.5 mg/kg) injection. Complete obstruction
was created by ligating the urethra with 6-0 nylon, resulting in a
progressive bladder distention. Female mice were used exclusively
because of relative ease of creating surgical obstruction. Although
urethral obstruction is possible in male mice, it requires a more
extensive manipulation of bladder and urethra due to the presence of
various male sex organs (prostate, seminal vesicle), which may create a
greater degree of local inflammation. Currently, there is no data,
either clinical or experimental, that implicate a
differential obstructive response in bladder between sexes. No specific
hydration or diuresis was performed. Animals recovered from anesthesia
and were maintained with an ad libitum supply of standard mouse diet
and water. Sham-operated mice served as negative controls
(n = 3) for bladder obstruction, where
bladder and urethra were identically manipulated and dissected but left
unobstructed. Unoperated, normal mice served as additional negative
controls (n = 3). Bladder tissues were
harvested after 3, 6, 12, and 24 h of obstruction
(n = 6 for 24-h obstruction and
n = 3 for other time points). To
localize the site of COX variation, epithelial and stromal layers were
separated by microscopic dissection. Whole bladders were also obtained
for both normal (n = 3) and
obstruction as above (n = 2 for each
3, 6, and 24 h time points) for histological analysis and Western
immunoblot analysis.
Regional bladder distention. A model
of local bladder distention was used to study the role of wall stretch
in COX-2 induction (40). A polyethylene ring (8 mm length, 4 mm width)
was placed around the proximal half of the bladder, and the urethra was
ligated as above, resulting in bladder distention confined to the
distal half (n = 4). After 4 h of
obstruction, tissue was harvested for reverse transcription-polymerase
chain reaction (RT-PCR) from the proximal and distal portions of the
bladder. Tissue was also harvested from similar regions of the negative
control (no obstruction) and positive control (conventional
obstruction) bladders (n = 2 for
each).
Tissue handling. Dissected tissues (1- to 3-mm2 pieces) were transferred
into 100 µl guanidine isothiocyanate (GITC) buffer (4 M GITC, 25 mM
sodium acetate, 0.8%
-mercaptoethanol, pH 6.0), snap frozen in
liquid N2, and stored at
80°C for RT-PCR analysis. Whole bladders for immunoblotting
were snap frozen in liquid N2 and
stored at
80°C. For histological analysis, bladder tissues were harvested into 10% formalin, and 4- to 6-µm paraffin sections were stained with hemotoxylin and eosin.
RNA isolation and cDNA preparation.
Samples in GITC were thawed on ice and sonicated for 10-15 s.
Twenty micrograms of ribosomal RNA from Escherichia
coli (Boehringer-Mannheim, Indianapolis, IN) were added
as a carrier, and 100 µl of sonicated samples were layered onto a
discontinuous cesium chloride gradient (100 µl of 97% and 20 µl of
40% CsCl in 25 mM sodium acetate). Samples were centrifuged for 2 h at
300,000 g using Beckman TLA-100
ultracentrifuge (Beckman Instruments, Fullerton, CA). RNA pellets were
redissolved in 0.3 M sodium acetate and precipitated with 100%
ethanol. Reverse transcription was performed in the presence of 100 U
monkey murine leukemia virus reverse transcriptase (Superscript;
GIBCO-BRL, Gaithersburg, MD), 0.5 µg oligo(dT) (Pharmacia,
Piscataway, NJ), 20 U RNAsin (Promega Biotech, Madison, WI), 10 mM
dithiothreitol, 0.5 mM dNTP (Pharmacia), and 1% bovine serum albumin
(BSA, Boehringer-Mannheim) with the buffer provided by the manufacturer
(total volume, 20 µl). Prior to adding RT, dNTPs, and BSA, reaction
mixtures were incubated at 65°C for 5 min to allow the oligo(dT)
primer to anneal to the poly(A) tail of mRNA. cDNA was synthesized at
42°C for 1 h and then precipitated with linear acrylamide, 4 M
ammonium acetate, and 100% ethanol. The pellets were redissolved in
20-40 µl of tris(hydroxymethyl)aminomethane-EDTA (Tris-EDTA)
buffer.
Primer selection and PCR. Primers were
selected based on previously published murine or rat COX-1 (8), COX-2
(15), and human
-actin (11) sequences found through GenBank database search. In initial studies, primer pairs were verified to yield a
single product of expected size. The COX-1 primers used were as
follows: sense, 5' CTG CTG AGA AGG GAG TTC CAT 3' (bp
602-621); antisense, 5' GTC ACA CAC ACG GTT ATG CT 3'
(bp 981-1,000), amplifying an 398-bp product. A 584-bp COX-2
fragment was amplified using the following primers: sense, 5' ACA
CTC TAT CAC TGG CAT CC 3' (bp 1,229-1,248); antisense,
5' GAA GGG ACA CCC TTT CAC AT 3' (bp 1,794-1,813). A
350-bp
-actin product was amplified using the following primers:
sense, 5' AAC CGC GAG AAG ATG ACC CAG ATC ATG TTT 3' (bp
383-413); antisense, 5' AGC AGC CGT GGC CAT CTC TTG CTC GAA
GTC 3' (bp 703-733). PCR reactions were performed in the
presence of 200 µM dNTP, 10 mM dithiothreitol, 50 mM KCl, 1.5 mM
MgCl2, 10 mM
Tris · HCl (pH 8.3), 0.001% gelatin, 0.5 pmol of
each primer, 1.25 U AmpliTaq DNA
polymerase (Perkin-Elmer Cetus, Norwalk, CT), 1.5 µCi
[32P]dCTP (Amersham,
Arlington Heights, IL), and 1-5 µl of tissue cDNA (total volume
50 µl). After initial denaturation at 94°C for 3.5 min, PCR
amplification was performed for 30-32 cycles at 94°C
(denature), 56-58°C (anneal), and 72°C (extend) for 1 min
each. An additional 8-min incubation at 72°C was done before completion.
PCR product confirmation and semiquantitative
assessment. After amplification, PCR products were
subjected to size separation by polyacrylamide gel electrophoresis.
Product identity was further confirmed by restriction digest of PCR
products using standard commercially available enzymes. For example,
based on published murine COX-2 sequences,
Pst I and
Hinf I (both from Boehringer-Mannheim) were expected to cut our COX-2 RT-PCR products into 240/340 and 190/390
base pair fragments, respectively. COX-1 and
-actin products were
confirmed in a similar fashion. A limiting dilution method was used to
make semiquantitative comparisons between cDNA samples, with PCR
reactions performed on 1:1, 1:10, 1:100, and, if necessary, 1:1,000
dilutions. Product abundance was assessed in the limiting concentration
range. All samples were normalized for
-actin expression. Band
intensity was determined with Phosphor Analyst software on GS-250
Molecular Imager System (Bio-Rad, Hercules, CA). Positive controls for
each COX-1 and COX-2 PCR assay were cDNAs obtained from adult mouse
kidneys. Water and dissection medium blanks were run as controls for
cDNA contamination.
Western immunoblot analysis. The whole
bladders were thawed on ice and homogenized. The protein concentration
of the bladder lysates was determined by spectrophotometric assays
using commercial colorimetric reagents (Bio-Rad). The lysates were
heated to 100°C for 10 min to cause denaturation. Proteins (75 µg
total) were then subjected to electrophoresis under reducing conditions
in 7.5% sodium dodecyl sulfate-polyacrylamide gels and transferred to
a nitrocellulose membrane (Bio-Rad) using the LKB Multiphor II semidry
electrophoresis apparatus (Pharmacia). The blot was initially blocked
for 2 h in Tris-buffered saline (pH 7.5) containing 3% nonfat dry
milk, followed by incubation for 30 min with the rabbit anti-murine
polyclonal antibody to COX-2 (Cayman Chemical, Ann Arbor, MI) at 1:500
dilution. The second antibody was a horseradish peroxidase-conjugated
goat anti-rabbit immunoglobulin G (Bio-Rad) at 1:25,000 dilution. Blots
were developed using the ECL chemiluminescent reagent (Amersham) and
subjected to autoradiography as directed by the manufacturer.
 |
RESULTS |
Confirmation of COX-1 and COX-2 mRNA in
bladder. Both COX-1 and COX-2 mRNA were detectable at
low levels in normal adult bladders by RT-PCR. cDNAs from bladder
yielded products of the expected band size for
-actin (350 bp),
COX-1 (398 bp), and COX-2 (584 bp), with minimal contaminating bands.
Product identity was further confirmed by specific restriction digests,
which yielded the expected fragment sizes. An example for COX-2 RT-PCR
product confirmation is shown in Fig. 1.

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Fig. 1.
Confirmation of cyclooxygenase-2 (COX-2) reverse
transcription-polymerase chain reaction (RT-PCR) products obtained from
murine bladders. Product was of expected size (584 bp) and was
completely digestable in a sequence-specific manner by restriction
endonucleases Pst I and
Hinf I. Positions of restriction sites
within COX-2 PCR product are shown by arrows. Identity of COX-1 RT-PCR
product was confirmed in a similar manner.
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COX-2 expression during fetal bladder
development. Semiquantitative RT-PCR analysis for COX-2
mRNA expression during fetal bladder development revealed the highest
level at E11.5 (~100-fold higher
than adult, based on
-actin normalization). COX-2 expression levels
remained above the adult levels throughout fetal development, although
they declined progressively through subsequent gestational time points.
Levels at birth (E20.5) were similar
to that seen in adult bladder (Fig. 2).

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Fig. 2.
RT-PCR analysis demonstrating the pattern of COX-2 mRNA expression
during fetal bladder development. Day of conception is designated as
embryonic day 0 (E0.0), and the litter is typically
born at E20.5. At
E11.5, bladder progenitor tissue, the
cloaca, at the site of the nephric duct entry, was used for analysis.
Comparably sized full-thickness bladder tissues were microdissected
from embryos at each later gestational time point. Quantitative
comparison of RT-PCR product abundance was made by normalizing for
-actin expression. COX-2 mRNA levels were highest at
E11.5, progressively declining through
subsequent gestational time points to low levels seen in adult
bladders. Representative assay from 3 different experiments is shown.
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COX-1 and COX-2 expression after bladder outlet
obstruction. At all time points of obstruction,
bladders were markedly distended on gross inspection compared with
those from control animals. Sham-operated mice had bladders that were
normal in appearance after 24 h. Histological examination of
obstructed bladders by routine hemotoxylin and eosin staining after 3 and 6 h of obstruction did not reveal any inflammatory
infiltrate, although occasional areas of inflammatory cells (mostly
neutrophils) and tissue necrosis were detectable at 24 h of
obstruction.
Semiquantitative comparison of COX-2 RT-PCR product abundance based on
-actin normalization revealed a median 30.2 ± 5.6-fold relative
increase (n = 6, P < 0.01) in bladders obstructed for 24 h compared with controls (Fig. 3). COX-2
levels did not differ between sham-operated and normal bladders. COX-1
levels, in contrast, did not change with obstruction (Fig.
4). When epithelial and stromal layers were
separated by microscopic dissection and analyzed by RT-PCR, COX-2 mRNA
was detectable in both at low levels under basal conditions. After
obstruction, the induction of COX-2 occurred predominantly in the
stromal layer (Fig. 5). In the time-course experiments (n = 3 for each time
point), COX-2 mRNA levels reached the peak between 3 and 6 h of
obstruction, and they gradually declined thereafter (Fig.
6). COX-2 induction was confirmed at the
protein level by Western immunoblotting analysis. COX-2 protein (~72
kDa) was not detectable in any of the control bladders
(n = 3), whereas progressively
increasing levels were seen with increasing duration of bladder
obstruction (Fig. 7).

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Fig. 3.
RT-PCR analysis demonstrating COX-2 mRNA induction after 24 h of
complete bladder outlet obstruction. Normal and sham-operated animal
bladders served as negative controls. Based on normalization for
-actin expression, median 30.2 ± 5.6-fold induction
(n = 6, P < 0.01; samples
1 and 2 are shown in
this autoradiograph) of COX-2 mRNA was seen after 24 h of bladder
obstruction.
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Fig. 4.
RT-PCR analysis of COX-1 levels after bladder outlet obstruction.
Compared with the control bladder (designated as 0-h obstruction), 3-, 6-, and 24-h obstruction resulted in no significant change.
Quantitative comparison was made by normalization for -actin
expression.
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Fig. 5.
RT-PCR analysis demonstrating localization of COX-2 mRNA induction
after complete bladder outlet obstruction to stromal layer.
Representative assay from 3 separate experiments is shown.
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Fig. 6.
RT-PCR analysis demonstrating pattern of COX-2 mRNA induction after
variable duration (0, 3, 6, and 24 h shown) of complete bladder outlet
obstruction. PCR product abundance consistently peaked between 3 and 6 h of obstruction, gradually declining thereafter. Quantitative
comparison was made by normalization for -actin expression.
Experiment shown is representative of 3 studies.
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Fig. 7.
Western immunoblot analysis of COX-2 induction after variable duration
of complete bladder outlet obstruction. After whole bladder tissue
lysates were separated (total 75 µg protein/lane) using sodium
dodecyl sulfate-polyacrylamide gel electrophoresis, proteins were
transferred onto a nitrocellulose membrane. They were then hybridized
with 1:500 rabbit anti-murine COX-2 polyclonal antibody. Blots were
developed using ECL chemiluminescent reagent. Lanes C
1-C 3, 3 normal bladders as negative controls.
Rest are bladders after 3, 6, 12, and 24 h of obstruction.
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In the experiments in which bladders were locally distended
(n = 4), COX-2 was induced to a
greater degree in the distal portion (distended) than in the proximal
portion (nondistended) within the same bladder (Fig.
8). Similar analysis of COX-2 expression in
both negative and positive control bladders did not reveal any regional
differences between distal and proximal halves.

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Fig. 8.
Effect of local bladder distention on COX-2 expression. Polyethylene
ring (4 × 8 mm) was placed over proximal half of bladder, and
urethral obstruction was performed as before, resulting in distended
distal (D) half and nondistended proximal (P) half within same bladder.
Bladder tissue from each region was analyzed for COX-2 expression by
RT-PCR. Similar regional analysis was performed in negative control
(normal) and positive control (total distention) bladders. Tenfold
dilutions were performed for each sample to make appropriate
quantitative comparisons.
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 |
DISCUSSION |
Our study clearly demonstrates that bladder wall stretch caused by
complete outlet obstruction stimulates the expression of inducible
cyclooxygenase, COX-2, at both mRNA and protein levels. In contrast,
expression of the constitutive isoform, COX-1, was low (close to the
detection limit by RT-PCR) under basal conditions, and it remained
unaffected by obstruction. COX-2 mRNA induction was seen at the
earliest time point that was examined (at 3 h of obstruction), and it
reached the peak at 6 h. Thereafter, a gradual fall in COX-2 mRNA
levels was seen with a longer duration of obstruction. This time course
of bladder COX-2 induction after obstruction is consistent with an
immediate early type of gene expression pattern. Immediate early genes
are thought to be activated rapidly and transiently by extracellular
stimulation to encode proteins that will participate in regulating
transcription of other genes. COX-2 activation pattern in fibroblasts
has also been described as an immediate early type, and there is
evidence that COX-2 expression is regulated by both transcriptional
activation and mRNA stabilization (7). The mechanism for gradual
downregulation of COX-2 mRNA with longer obstruction is not known, but
COX-2 mRNA is known to be short-lived (7). It is possible that some downstream COX-2 product may repress COX-2 transcription in a negative
feedback fashion.
Although COX-2 message was detectable in both epithelial and stromal
layers, its induction after obstruction occurred in the stromal layer.
Our study does not identify the exact cell type responsible for COX-2
induction, but we believe that smooth muscle cells are a likely
candidate for COX-2 activation in response to mechanical stretch.
Previous studies have shown that mechanical stretch induces COX-2
expression in vascular smooth muscle cells (32) and in renal mesangial
cells, mesenchymal cells of probably smooth muscle lineage (1). COX-1
levels did not change in renal mesangial cells after stretch
stimulation (1), similar to our findings. Inflammatory cells (e.g.,
macrophages) may have contributed to COX-2 induction, but histological
examination of the obstructed bladders did not reveal any inflammatory
infiltrate after 3 and 6 h of obstruction, the time points at which
COX-2 induction was the greatest. Increased wall tension due to
elevated intravesical pressure may also have caused COX-2 induction.
However, the difference in COX-2 levels between distended and
nondistended portions within the same bladder argues against the
involvement of either inflammation or elevated intravesical pressure in
COX-2 stimulation, since presumably, the intravesical pressure
elevation should be equal within the same bladder and the degree of
inflammation similiar even if only a part of the bladder is distended.
Thus it seems reasonable to infer that local mechanical stretch plays a
key role in COX-2 activation in bladder smooth muscle cells.
The COX-2 induction in bladder after obstruction represents
reactivation of a gene that is highly expressed during fetal
development. COX-2 mRNA level was nearly 100-fold higher for equal
tissue mass at E11.5 than in newborn
or adult bladders. At this gestational time point, the bladder
progenitor cloaca is divided by the descending urorectal septum, and
the lower urinary tract begins to form (36). The function of COX-2 in
bladder development is not known, but its involvement in the local
regulation of proliferation and/or apoptosis is possible. COX-2
expression can be stimulated by growth factors and mitogens (7), and
COX-2 has been implicated in modulating apoptotic pathways (18, 37).
Previous studies have established that bladder PG synthesis is
stimulated by distention. Bladder PG synthesis was first reported by
Gilmore and Vane (9) in 1971, who observed an elevation of circulating
PGE2 after bladder distention.
Distention of whole rat bladders in vitro results in an intraluminal
increase of PGI2, PGE2, and thrombaxone
A2 (13). The type of PG produced
by the bladder varies somewhat with species, but
PGE2 and
PGI2 seem to be the predominant
products in human, rabbit, and rodents (12, 13, 16). Increased PG
synthesis after local distention may be a common response of hollow
organs. Similar observations have been made for aorta (32) and gall
bladder (30). Our data suggest that such increase in bladder PG
synthesis after distention may occur, in part at least, by induction of
COX-2 gene expression.
Urinary PGs may be involved in the modulation of micturition reflexes.
Early experiments documented ability of prostaglandins to induce a
slow, tonic contraction of bladder smooth muscle cells in vitro (2).
Topical application of PGE2 onto
quiescent rat bladders in vivo was shown to induce a series of reflex
bladder contractions (19). Similarly, in human subjects, intravesical instillation of PGs into the bladder lowers the volume threshold for
bladder contractions, thus lowering the capacity (2, 3). Pharmacological inhibition of prostaglandin synthesis using COX inhibitors (e.g., indomethacin) has been found to lower the bladder tone in vitro (2) and to increase the bladder capacity and compliance
in vivo (23). The effects of COX inhibitors can be reproduced by
selective PG receptor antagonists (22). One of the potential local
target of PGs may be the capsaicin-sensitive primary afferent nerve
fibers in the bladder (22, 24). There is evidence that prostaglandins
can sensitize capsaicin-sensitive nocioceptive pathways by directly
acting on nerve terminals (10). PG ability to trigger reflex bladder
contractions is abolished when animals are pretreated systemically with
capsaicin, an agent that selectively destroys a category of
nonmyelinated afferent nerve fibers (24, 34). In human studies, the
prerequisite requirement for PG effects in the bladder seemed to be the
presence of intact neural pathways, further suggesting its role in
activation of neural target cells (2, 3).
COX-2 induction in the bladder in response to obstruction may have
significant clinical implications. It is a well-documented clinical
phenomenon that the bladder responds to obstruction by developing
hyperactivity of micturition reflexes (27). The precise molecular
mechanism by which this phenomenon occurs is not known. The current
study demonstrating COX-2 induction in the bladder after obstruction
suggests an attractive hypothesis. That is, increased local
prostaglandin synthesis, secondary to COX-2 induction, triggers reflex
bladder contractions in the obstructed bladder. This hypothesis may be
applicable to various syndromes of bladder outlet obstruction such as
benign prostatic hyperplasia.
Cellular proliferation and hypertrophy is another adaptive response of
the bladder to outlet obstruction (14, 17). A similar proliferative
response is seen in the heart when it is subjected to increased
workload and mechanical stretch (41). Various immediate early genes
have been shown to be activated, including genes primarily expressed in
the fetal period (14, 33, 41). Our data demonstrate that COX-2 is
highly expressed during the period of active proliferation and
differentiation in fetal bladder development. Thus COX-2 induction, shown to be associated with various settings of cell proliferation, may
also play a role in the development of pathological bladder hypertrophy
and hyperplasia in chronic partial obstruction.
Several studies have shown significant improvements in patients with
idiopathic detrusor instability using COX inhibitors (e.g.,
indomethacin), but most patients could not sustain the treatment due to
high incidence of side effects, particularly gastric discomfort
(3). All the COX inhibitors currently in clinical use are
isoform nonspecific, inhibiting both COX-1 and COX-2 (4, 38). Gastric
mucosal cytoprotection is thought to be regulated by COX-1, and COX-2
specific inhibitors may be able to provide desired COX inhibition in
the inflammatory and proliferative conditions without unwanted
gastrointestinal side effects (26). COX-2 specific inhibitors,
currently a focus of intense research in major pharmaceutical
industries (38), might also be efficacious in reducing pathological
changes associated with bladder outlet obstruction.
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ACKNOWLEDGEMENTS |
This work was supported by National Institute of Diabetes and
Digestive and Kidney Diseases Grants DK-37448, DK-39255, and DK-40042.
J. M. Park was supported in part by the American Foundation for
Urologic Disease and in cooperation with Bard Foundation.
 |
FOOTNOTES |
Address for reprint requests: J. P. Briggs, George M. O'Brien Renal
Center, 1150 West Medical Center Drive, 1560 Medical Science Research
Bldg. II, Ann Arbor, MI 48109-0676.
Received 15 January 1997; accepted in final form 5 June 1997.
 |
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