Gallbladder contractility in aspirin- and cholesterol-fed prairie dogs

Gallbladder Contractility Prairie Dogs YONG F. LI,*

DIANE H. RUSSELL,* and FRANK G. MOODY*

in Aspirin- and Cholesterol-Fed

STUART

I. MYERS,?

NORMAN

W. WEISBRODT,§

Departments of *Surgery and “Physiology, University of Texas Medical School at Houston, Houston; and tDepar&ment of Surgery, University of Texas Southwestern Medical School, Dallas, Texas

Background/Aims: Whether aspirin prevents cholesterol gallstone formation is controversial. This study aimed to investigate this issue and determine the depression of gallbladder smooth muscle contractility associated with cholesterol feeding in the prairie dog. Methods: Prairie dogs were divided into four sub groups. Animals were fed control or 1.2% cholesterol diet and treated with placebo or aspirin for 2 weeks. The presence of crystals and stones was determined, and contractile force in response to cholecystokinin octapeptide (CCK-8) of gallbladder muscle strips was measured. Results: Maximal stress of 2.66 t 0.23 x lo4 N/m2 was measured in muscle strips from animals on control diet. Maximal stress was significantly lower in strips from animals on high-cholesterol diet, being 1.49 r 0.16 x lo4 N/m2 with placebo and 1.62 t 0.23 x lo4 N/m2 with aspirin. The difference in maximal stress between aspirin-treated and placebo-treated animals was not significant. Although none of the animals on control diet had crystals or stones, all animals on the high-cholesterol diet, whether receiving placebo or aspirin, had crystals in the bile, and more than 65% had cholesterol stones. Conclusions: Aspirin has no effect on stone formation, nor does it prevent the decrease in contractility despite a profound decrease in endogenous gallbladder prostanoid synthesis.

fects of aspirin examined.

of abnormalities

have been

documented

during the early periods of cholesterol crystal and stone formation in the gallbladders of prairie dogs fed a lithogenic diet. They include decreased gallbladder muscle contractilitylm3 and increased prostaglandin synthesis and mucus secretion. 4-8 Initially, aspirin was found to interrupt this series of events in the prairie dog, reducing the amount of glycoprotein secreted by the gallbladder slices and completely blocking the formation of crystals and stones in spite of the presence of lithogenic bile.” However, more recent studies have shown that aspirin fails to reduce the incidence of cholelithiasis in the prairie dog model’O~‘l and that inhibition of prostaglandin synthesis by indomethacin fails to prevent gallbladder mucin hypersecretion in cholesterol-fed prairie dogsI The ef-

study was designed

to explore the

one aspect of motility,

gallbladder

week period

and gallstone

of aspirin

formation

after a 2-

administration.

Materials and Methods A group of 28 male prairie dogs (R Zoo, Neshkoro, WI), weighing 0.7 - 1.2 kg, were caged in rooms maintained at 23°C with alternating Animals

were allowed

After a l-week domly

12-hour

periods

continuous

equilibration

into four subgroups.

of light and dark.

access to food and water.

period,

they were divided

ran-

1 (n = 6) and 2 (n =

Subgroups

6) consumed a control diet containing trace cholesterol ad libitum, and subgroups 3 (n = 6) and 4 (n = 10) consumed a diet enriched with 1.2% cholesterol ad libitum (Teklad diet; Harlan Sprague-Dawley, Madison, WI). The major ingredients (g/kg food) of the cholesterol diet were soy assay protein, 172.3; sucrose, 447.2; corn starch, 139.0; corn oil, 9.7; egg yolk powder,

146.4; cholesterol,

8.6; cellulose,

mix 40.0; and flavor (sessalom)

1.0. Children’s

ange-flavored ground

daily and suspended

was administered

orally with a plastic

by fully conscious,

unrestrained 4 received

pipette

pipette

2, and 8 of the 10 animals

mals of subgroup directly

chewable

or-

in 1 mL of water to provide

for 2 weeks. This feeding

Chemical

25.8; mineral

aspirin tablets (Bayer Co., New York, NY) were

average dose of 100 mg . kg-’ . day-’ per animal.

morning

number

have not been

between

contractility,

of subgroup

A

motility

The present

relationship muscle

on gallbladder

animals.

to all animals

of subgroup

method

an

This volume 4 each

was well accepted

The remaining

daily acetylsalicylic

2 ani-

acid (Sigma

Co., St. Louis, MO) at the same dosage level mixed into their chow. to all animals

Placebo

was administered

of subgroups

At the end of the 2-week feeding anesthetized

with sodium

tories Inc., Fort Dodge,

daily by

1 and 3. period,

pentobarbital

IA) (30 mg/kg

the animals

(Fort Dodge intraperitoneally),

were

Laboraand

the abdomen was opened. The cystic duct was ligated and the gallbladder removed. Bile was withdrawn from the gallbladder,

Abbreviations used in this paper: CCK-S, cholecystokinin octapeptide; ED%, median effective dose; EGTA, ethyleneglycol-bis(paminoethylether)N,N,W,N-tetraacetic acid. 0 1994 by the American Gastroenterological Association 0019-5085/94/$3.00

GALLBLADDER CONTRACTILITY AND ASPIRIN

June 1994

and one drop was examined cholesterol amined

crystals.

along

with

the bile for the presence

stones, defined as macroscopically tudinal

was then opened

The gallbladder

with

In all animals

piece of the gallbladder prostaglandin

and ex-

Two longi-

were used for measur-

except

5 in subgroup

4, a

tissue was saved for determination

and used for determination

stones

and of prostaglandin

regular

diet plus placebo (subgroup

placebo (subgroup

of

synthesis.

The animals

(subgroup

among

of crystals and were fed

1, n = 5), regular

2, n = 5), and cholesterol

diet

diet plus

3, n = 1). The diet and the administration

were the same as described

for animals

in the first

group. To determine salicylate

the length

levels,

administered

a third

after the fourth (Abbott

group

elevation

of 4 male prairie

20 minutes

and 2,4,

daily dose of aspirin

Diagnostics,

cence polarization peutic

of systemic

Irving,

immunoassay

drug and hormone

using

The technique mounted

optimal

was determined (carbachol,

technology

for measuring described.* length

uses fluores-

to monitor

thera-

by stimulating

contractility

muscle

strips

were

solution,

with carbamylcholine Isometric

contractile

(CCK-8)

to 1.5 X IO-’ mol/L; Sigma) was recorded,

(L,)

of microsomal

and prostanoid previously

analysis

described

membrane

of microsomal

including

to the as stress.

potassium

buffer, 100 mmol/L,

phosphate

N-tetraacetic

nated

the

The

Amersham

Co., Ar(Sigma)

experiments

identified

of cycle-oxygenase

to 3 volumes

in subgroups

Pittsburgh,

1 and 3.‘“.”

incubation,

the reaction

was termi-

to pH 3 with

4N formic

acid (Fisher

PA). The reaction

mixture

then under-

two times with 2 volumes of ethylacetate

ter Diagnostics

Inc., McGaw

and reconstituted

(2:1, vol/vol)

(Fisher

were then subjected

in two

solvent

systems.

to thin-layer

A9

is the

2O:lOO) (2,2,4_trimethylpentane

plates

Co., Ann Arbor, B, [TXBJ

and identified

prostanoid

by iodine

was

counted

(Aquassure;

DuPont

NEN,

the rabbit

donic acid converted

acid/water (Cay-

of prostaglandin PGE2, PGD,

vapor. The radioactive standards

and

in

liquid

zones

were cut, and their scintillation

cocktail

Boston, MA) with a liquid scintil-

(LKB 1217; LKB Instruments,

MD). Data are presented

of

(100:50:

standards

MI; purity

of 6-keto-PGF?,,

to the prostanoid

counter

phase

2 99%) were added to the thin-layer

radioactivity lation

organic acid/water

and acetic acid; Fisher Scien-

unlabeled

EPG] A1 2 98%; purity thromboxane

The microchromatogra-

C is chloroform/methanol/acetic Authentic

was

with chloro-

Scientific).

ethylacetate/2,2,4-trimethylpentaneiacetic tific)22; system

(Bax-

Park, IL). The supernatant

dried under nitrogen,

have been

ani-

(indo-

went extraction

phy

of

with

Sigma) was used in the enzyme experi-

as the percentage

to individual

Gaithersburg, of labeled

arachi-

or total prostanoid

peaks prostan-

oids are presented.

of oxygenated

pH 7.4 at 4°C with

Statistics

ethyleneglycol-bis(@aminoethylether)-N,iV,N’, acid (EGTA)

(to chelate

The median

Ca*+, thus inhibiting subgroup

effective

was determined

dose (ED,,,) of CCK-8

from geometric

any calcium-dependent tissue phospholipases), and 1% fatty acid-poor bovine serum albumin (Calbiomed Inc., San Diego,

analysis.‘4.‘5 The ED,,+, maximal

CA) to adsorb

arachidonic

was minced,

was incubated

to be well in excess and to not limit

by acidification

Scientific,

of approxi-

of L-epinephrine

Preliminary

An inhibitor

lo-minute

corresponding

fractions

from control and cholesterol-fed

and added

mmol/L

as controls

After

suspension

IL) in the presence

this level of substrate

PCR

by the method

(mean _’ SEM). Only data for the six major primary

mals were weighed 10

Heights,

consisting

acid (98.1%;

at 37°C for 10 minutes.

man Chemical

fractions.

by radiochromatography

gallbladder.‘4m19 Harvested gallbladders

lington

force in

(1.5 X lo-”

membrane

for several tissues,

0.75 pg of I’?Jarachidonic

(90:8:1:0.8).21

Prostaglandin Synthesis Determinations for preparation

as determined

Lowry et al.‘” The microsomal

of the tissue.

FL). Each tube received

suspension,

chloride

correlated

area of each muscle strip, and expressed

Preparation

Inc., Gainesville,

0.1 mg of protein

in 100

tubes (Prosil-28;

100 ILL of the microsomal

collected,

gallbladder

wet weight

mately

somal extracts

In brief,

octapeptide

Chemical

acid-poor

buffer, pH 7.4, at 4°C in a vol-

were mixed in siliconized

form- methanol

for active force development

response to cholecystokinin

methods

Reactants

or fatty

was resuspended

ume equal to one fourth the original

ments

was

EGTA

The pellet

phosphate

dogs

levels clinically.”

lo-> mol/L; Sigma).

cross-sectional

potassium

10 mmol/L;

in organ baths filled with Krebs-Ringer’s

and muscle

mmol/L

without

albumin.

methacin,

the TDx System

system

buffer

serum

of serum

Contractility Measurements has been previously

bovine

CA). The surface of the mi-

pellet was carefully washed with 100 mmol/L potas-

phosphate

synthesis.

8, 12, and 18 hours

TX). This

Inc., Fullerton,

prostanoid

daily doses of aspirin for 4 days. Serum salicylate

levels were measured

crosomal

Research

A second group of 11 male prairie dogs were divided

plus aspirin

man Instruments sium

synthesis.

the four subgroups

of aspirin

for

of cholesterol

visible sediment.

strips cut from each gallbladder

ing contractility.

microscopy

polarizing

1663

any released

arachidonic

and the resulting

on ice with an ultraturrex

acid.‘“-”

suspension

homogenizer

The tissue

was homogenized

(Tekmar

Inc., Cincin-

nati, OH) and spun at SOOOg for 15 minutes in a Sorvall RC5B centrifuge (DuPont Instruments, Doraville, GA) at 4°C. The supernatant was removed at 105,OOOg in a refrigerated

and centrifuged ultracentrifuge

for 65 minutes (L2-750; Beck-

acid converted

were compared multiple dence

by analysis

range procedure

of stone

and crystal

stresses,

to individual of variance among

means

and percentages

of

or total prostanoids with

a Duncan’s

four subgroups.

formation

in each by probit

new

The inci-

in each subgroup

was

compared by Fisher’s Exact Test. All data are presented as mean ? SEM. A P value 5 0.05 was considered statistically significant.

1664

GASTROENTEROLOGY Vol. 106, No. 6

LI ET AL.

prostanoid

synthesis

1, the control

are shown

microsomes

in Table

converted

donic acid to all major primary keto-PGF,,,

PGE2, PGF?,,

total conversion gallbladder

26 min

2 h

4h

12 h

6 h

2, treatment

of the control decreased

18 h

flgure 1. Serum salicylate levels after aspirin administration.

Serum salicylate levels are shown for four prairie dogs fed aspirin (100 mg,kgl.day-I) for 4 days. Twenty minutes and 2, 4, 8, 12, and 18 hours after the last dose of aspirin, blood was withdrawn and salicylate levels were measured. Elevated serum salicylate levels were observed, with levels peaking at variable intervals from animal to animal.

13.9%

of the other major prostanoids.

day-‘)

and

were well tolerated

the 2 weeks.

There

hepatotoxicity, experimental

aspirin

(100

by the prairie

was no evidence

weight

mg. kg-‘. dogs during

of regurgitation,

loss, or hemorrhage

during

the

period.

Serum salicylate levels after the last dose of aspirin given to animals treated for 4 days are shown in Figure 1. Administration

of this dose resulted

in elevated serum

salicylate levels lasting up to 12 hours. These levels peaked at variable intervals from animal to animal. Total gallbladder

prostanoid

synthesis

and individual

prostanoid

conversion,

by 35%, although In subgroup

a sig-

3, feeding

Total gallbladder

micro-

somal prostanoid synthesis (21.6% -+ 5.0%) was not altered when compared with the controls. However, for from

indomethacin diet

microsomal

the prairie dogs with the cholesterol diet for 2 weeks decreased synthesis of PGEL but did not alter synthesis

In subgroup

Cholesterol

decreased to-

by 62%. In subgroup

prairie dogs with oral aspirin

level was not reached.

microsomes

Results

of the control

PGEz, PGFza, and PGDz synthe-

? 3.8%, was decreased

nificance

6-

PGD2, PGA2, and TXB2; the

synthesis

significantly

arachi-

including

with indomethacin

prostanoid

sis. Total gallbladder

i

04

prostanoids

was 2 1.3%. Preincubation

microsomes

tal gallbladder

1. In subgroup

14C-labeled

cholesterol-fed

in vitro,

animals

synthesis

4, administration

treated

was inhibited of aspirin

with

by 37%.

to prairie

dogs

on cholesterol diet significantly decreased the synthesis of the individual prostanoids and decreased total gallbladder microsomal prostanoid synthesis by 64% compared with the animals fed cholesterol diet alone. The incidence of crystal and stone formation is shown in Table

2. None

of the prairie

dogs fed control

diet

(subgroups 1 and 2) had cholesterol crystals or stones. However, the rates of occurrence of crystals and stones in animals

fed cholesterol-enriched

diet (subgroups

3 and

4) were significantly higher than those of the other two subgroups. Cholesterol crystals were found in the bile of

Table1. Gallbladder Microsomal Prostanoid Synthesis Conversion rate (%) 6-KetoPGFz,

PGFI,

PGE?

PGD2

PGA2

TXB?

Total PG

Regular diet + placebo + indomethacin (n = 11) Subgroup 2 (n = 11)

2.8 ? 0.5 1.1 5 0.3”

2.6 2 0.9 0.7 + 0.2”

6.2 2 1.5 0.9 2 0.3”

2.4 ? 0.4 0.8 ? 0.2”

1.4 2 0.2 1.1 ? 0.2”

0.7 2 0.1 0.5 5 0.1”

21.3 ? 3.6 8.2 * 1.3”

Regular diet + aspirin Subgroup 3 (n = 7)

1.4 2 0.4

0.5 & O.la

1.5 & 0.5”

0.6 + 0.2”

1.8 + 0.8

0.3 + 0.1

13.9 -+ 3.8

Cholesterol diet + placebo + indomethacin (n = 7) Subgroup 4 (n = 5)

1.3 + 0.3” 0.6 i 0.3”

1.5 2 0.6 0.7 2 0.3”

2.3 2 0.5” 0.9 + 0.2=

2.4 ? 0.8 1.3 2 0.4

3.1 2 0.8 2.7 2 1.2

0.8 2 0.2 0.7 2 0.2

21.6 2 5.0 13.6 2 0.4”

Cholesterol diet + aspirin

0.4 * 0.1”

0.5 IT 0.1

0.5 2 0.1”

0.6 2 0.1”

1.4 t 0.4”

0.3 t 0.1”

Subgroup 1 (n = 11)

8.0 + 2.1”

NOTE. Conversion rate data are calculated as nanograms of labeled arachidonic acid converted to individual or total prostanoid peaks per milligram of protein and are presented as percentage of the labeled arachidonic acid converted to individual or total prostanoid peaks. In subgroup 1,the control microsomes converted 14C-labeled arachidonic acid to all major primary prostanoids; total conversion (synthesis) was 21.3%. In subgroup 2, treatment with oral aspirin significantly decreased PGE2, PGF,,, and PGD? synthesis; total conversion was 13.9% 2 3.8%. In subgroup 3, after a high-cholesterol feeding, synthesis of total and all major individual prostanoids (except PGEJ was not altered. In subgroup 4, after administration of aspirin to the animals on high-cholesterol diet, total and all individual prostanoids syntheses were significantly decreased. In subgroups 1 and 3, preincubation with indomethacin decreased total gallbladder prostanoid conversion significantly. “P < 0.05 compared with subgroup 1.

GALLBLADDER

June 1994

Table 2. Crystal and Stone Formation

AND

ASPIRIN

1665

Table 3. Maximal Stress Developed

Crystals/total

Stones/total

o/11

o/11

O/11

O/l1

6/6”

4/6”

Subgroup 1 (n = 11) Regular diet + placebo Subgroup 2 (n = 11) Regular diet + aspirin Subgroup 3 (n = 6) Cholesterol diet + placebo Subgroup 4 (n = 10) Cholesterol diet + aspirin

CONTRACTILITY

lo/lo”

Maximal stress (Xl04 N/n?) Subgroup 1 (n = 6) Regular diet + placebo Subgroup 2 (n = 6)

8/10”

2.66 2 0.23 2.48 k 0.39

Regular diet + aspirin Subgroup 3 (n = 6) Cholesterol diet + placebo Subgroup 4 (n = 10) Cholesterol diet + aspirin

1.49 -c 0.16” 1.62 2 0.23”

NOTE. In subgroup 3 (cholesterol diet plus placebo) and subgroup 4 (cholesterol diet plus aspirin), crystal and stone formation were significantly increased compared with subgroup 1. (For subgroup 3, n = 6 rather than 7 because the bile sample was lost.) a/=’ < 0.05 compared with subgroup 1.

NOTE. In subgroup 3 (cholesterol diet plus placebo) and subgroup 4 (cholesterol diet plus aspirin), maximal stress developed by gallbladder was significantly lower than in subgroup 1. af < 0.05 compared with subgroup 1.

all the animals

stones

(subgroup

3, and

from prairie

of subgroups

3 and 4. Cholesterol

were also found in 4 of 6 animals 8 of 10 animals

(7 fed aspirin

from subgroup

from subgroup

via pipette,

1 via chow)

4.

developed

The relationship between gallbladder muscle stress and the dose of CCK-8 in the animals tested within each subgroup contracted

is depicted

in Figure

2. All gallbladder

in a dose-dependent

manner

to CCK-8.

(subgroup

stress developed (subgroup

3) aspirin, by strips

1). When

taken from animals was no difference rin (subgroup

_

compared

from animals

with

0.87 4.61

stresses for muscle

strips

diet were compared,

there

between

strips from animals

1) and strips from animals

X lo-”

given aspi-

given placebo

mol/L,

on the same diet regi-

(subgroup

3). mol/L, 2.85 +

6.63 2 1.97 X lo-”

mol/L,

and

Discussion A number

of studies

have been performed

to ex-

plore the roles of prostaglandins and gallbladder motility in gallstone formation in prairie dogs fed a high-cholesterol diet. Lee et al. reported that aspirin, an inhibitor of prostaglandin synthesis, prevented stone formation possibly by suppressing gators have emphasized

0-OCONTROL ?? -•CONTROL+ASA 3.007 A-ACHOLE. A-ACHOLE.+ASA

aspirin

aspirin

from that

from one another.

diet

maximal

by muscle from animals

different

? 0.98 X lo-” mol/L in subgroups 1, 2, 3, and 4, respectively. The values were not significantly different

maximal

on control

4) was not significantly

by muscle

diet with

The ED,,s were 3.39 +- 1.35 X lo-”

strips

on control

stress developed

dogs on high-cholesterol

men but not receiving

Maxi-

mal stress, shown in Table 3, was lower for strips from animals on cholesterol diet, with aspirin (subgroup 4) or without

(subgroup

2). The maximal

mucus secretion.’ Other investithe role of gallbladder stasis in

cholesterol stone formation, muscle contractility being tion.‘-’

with decreases in gallbladder observed before stone forma-

In light of these studies

and because prostaglan-

dins may affect smooth muscle contraction,26.27 the relationship between gallbladder muscle contractility and gallstone formation after a 2-week period of aspirin ministration was explored. Animals receiving aspirin in the present study

-10

-9

-8

CCK-OP

(Log M)

-7

Figure 2. Gallbladder contraction in response to CCK-8 showing active stress developing in response to CCK-8 by gallbladder muscle strips from prairie dogs on control or cholesterol (CHOLE.) diet, with or without aspirin (ASA) administration. Values are mean 2 SEM. The response in cholesterol-fed animals (subgroups 3 and 4) was significantly lowerthan that in the animals with control diet (subgroups 1 and 2).

adap-

peared to be in good health. These results are in accordance with the findings of Lee et al.’ who also used 100 as the maximal dose. To the best of our mg.kg-‘.day-’ knowledge, there are no published data regarding the pharmacokinetics of aspirin in prairie dogs. In humans, the elimination of salicylate is dose dependent and the plasma half-life for salicylate is 2 - 3 hours for low doses and about 12 hours for anti-inflammatory doses. The half-life of salicylate may be as long as 15 -30 hours at high therapeutic doses or when there is intoxication.28

1666

GASTROENTEROLOGY

LI ET AL.

Administration

of aspirin

resulted

levels that peaked at about 2-4

in serum

salicylate

hours after the last dose,

of Lee et al.” are unclear. chemical

composition

Vol. 106,

As was stated

of the gallstones

No. 6

by Lee, “The is the result

of

the prairie dogs used in our study. There was considerable

a hepatic defect because liver determines the chemical composition of bile. But the making of the concretion

variation

also depends

then returned

digestive

levels, perhaps

because

was given.

Salicylate

system

levels in serum

12 hours after aspirin

of maxi-

of variations

status of the gastrointestinal

elevated 3-12

levels by 18 hours in

in the exact time of onset and duration

mal serum aspirin

toward undetectable

administration,

in the

gallstones

were still

and

averaging

only explain

The method

used in our studies synthesis

First, it allows simultaneous thesis of all primary cross-reactivity.

Finally,

products.‘“.‘8,“.“1 cycle-oxygenase

with gallbladder terol-fed animals Aspirin

the method

system that minimizes

use of indomethacin

shows specificity

oxygenase

individual

of the biosyn-

Secondly,

separation

a known

of biosynthesis

For example, inhibitor,

as an in of cyclo-

indomethacin,

was preincubated

tissue taken from control and cholesand inhibited prostanoid synthesis.

administration

by gallbladder

measurement

prostanoids.

uses a chromatography

to measure

has several advantages.‘4-19

for 2 weeks decreased synthesis

tissue of the major individual

prostanoids

rather

Aspirin formation

than why stones

failed

of gallbladder Aspirin

as indicating

not be interpreted not affect patterns

by 35% and 64% in the control

contractility

diet. Thus, in spite

animals

compared

role for endogenous

the contractility

contractility

and

thesis was inhibited

by cholesterol

synthesis, both contractildoses of CCK-8 remained

They also are consistent

of a depressed

and stone

contractility

with

These results can be interpreted

no major

cholesterol-fed animals, respectively. This suppression occurred in spite of the fact that the gallbladders were

Total prostanoid

fed a regular

controls.

dins in regulating muscle.

crystal

induced

in the aspirin-treated

their respective

may

form at all.“”

also did not affect normal

of inhibition of prostaglandin ity and the median effective unchanged

bile

the depressed

muscle

of muscle from animals

The

in the gallbladder

not only to prevent smooth

distur-

functions.

that form are cholesterol

but also to prevent

feeding.

through

cholesterol-supersaturated

stone formation.

and PGD,.

defect, contractile

why the stones

syn-

such as PGEL, PGF2,,

and/or

are stones that are formed

(lithogenic)

stones,

and total prostanoid

on a gallbladder

in mucosal

when the

mg/dL.

vitro control

bances

smooth

with previous

findings

whenever

there is crystal and

On the other hand, as indicating

prostaglan-

of gallbladder

these data should

that prostaglandins

or force of gallbladder

contractions

vivo. Our study did not address these important

do in

aspects

harvested 24 hours after the last dose of aspirin, a time when serum salicylate levels were at their lowest. Taken

of gallbladder

together,

lesterol feeding significantly decreases gallbladder muscle contractility without changes in EDSo during stone for-

this information

mode of administration significantly inhibited Our results regarding rin and stone formation

indicates

that

the dose and

of aspirin used in these studies gallbladder prostaglandin synthethe relationship between aspidiffer from those of Lee et al.,”

who reported that none of the 15 prairie dogs in their experiments had crystals or stones in the bile after a (12%) feeding plus aspirin (100 mg . kg-’ .dayy’) for 2 weeks. This was in spite of the presence of cholesterol-saturated bile. Unlike these investi-

high-cholesterol

gators, we were unable to influence the incidence of crystals and stones in cholesterol-fed animals with aspirin. Observations similar to ours have recently been reported by other investigators. Cohen et al.,” using a comparable dose of aspirin, found it to be ineffective in preventing crystal or stone formation in either the prairie dog or the hamster model of lithogenesis. Additionally, Oleary et al. failed to inhibit cholesterol crystal formation in the prairie dog model using indomethacin, although prostaglandin synthesis by gallbladder explants was inhibited.” The reasons for the disparities between these recent studies and the original work

The present

motility. study confirms

previous

reports that cho-

mation ls2 and further implicates this alteration as an important factor in lithogenesis. There is abundant literature

documenting

abnormal

gallbladder

emptying,

in patients

stasis, with

as evidenced

by

gallstones.30-”

More specifically, muscle strips from human gallbladders with cholesterolosis or cholesterol gallstones have a reduced contractility compared with muscle strips from patients with pigment stones.‘* The decreased contractility in the cholesterol-fed prairie dog may help to explain these clinical

findings.

The mechanisms

responsible

for

the depressed gallbladder contractility in cholesterol-fed prairie dogs are uncertain but may be related to a change in actin isoforms in gallbladder smooth muscle after high-cholesterol feeding.35 In summary, our results confirm that high-cholesterol feeding in prairie dogs induces crystal and stone formation in the gallbladder and causes a decrement in gallbladder muscle contractility. Aspirin failed to prevent cholesterol stone formation and the reduced gallbladder contractility in spite of its inhibitory effects on prostaglandin synthesis. Thus, endogenous prostaglandins may

June 1994

not be involved

GALLBLADDER CONTRACTILITY AND ASPIRIN

in the reduced

gallbladder

cle contractility and the stone formation terol feeding in this animal model.

smooth

mus-

seen with choles-

References 1. Fridhandler TM, Davison JS, Shaffer EA. Defective gallbladder

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Received July 16, 1993. Accepted December 7, 1993. Address requests for reprints to: Yong Fang Li, M.D., Department of Surgery, Suite 4165, University of Texas Medical School at Houston, Houston, Texas 77030. Fax: (713) 792-5417. Supported by National Institutes of Health grants DK 38888 and DK 38342 and Stolpe Research Fund. This work was published in part in abstract form (Surg Forum 1989;40:157 and Gastroenterology 1990;98:A254).