An improved apparatus for intragastric titration in the conscious dog

An Improved Apparatus for lntragastric Titration in the Conscious Dog

M. J. DALY, R. W. HARTLEY, AND R. STABLES

An apparatus for automatic intragastric titration with on-line display of results has been described. The apparatus has been validated by titration of exogenous acid injected into the test meal in a reservoir and in vivo by assessing the secretory response of a dog with a gastric fistula to a test meal. A titration display unit provides a record of the secretory response both as a digital printout and a bar chart display. Cimetidine (2 mg kg-W’) significantly reduced the secretory response to a test meal. Stomach; lntragastric titration; Test meal; Cimetidine.

Key Words: INTRODUCTION Gastric

secretion

stimulus

is food.

can be induced

Measurement

by a variety

of agents

of gastric acid secretion

but the

most

in response

natural

to a test meal

has been carried out for many years. Early experiments involved removing small samples of the gastric contents at various times after ingestion of the test meal and titrating

these

samples

against

calculate

total acid secretion

contents

and this required

alkali

to determine

it was necessary

the acid content.

to measure

the assay of a marker

In order

the volume

substance

to

of the gastric

in each sample

(George,

1968). A major

advance

readministered

was

made

a proportion

by Fordtran

of the gastric

and

Walsh

contents

(1973)

by means

who

aspirated

of a mixing

and

syringe

connected to a Levin tube. The pH of the aspirate was monitored and an intragastric infusion of sodium bicarbonate solution varied manually to maintain the gastric pH at 5.5. The amount the amount

of alkali

infused

of acid secreted

in man and has also been adapted the method the alkali

suffers

infusion.

from

in a given

in that period.

period

was taken

This technique

as equivalent

has been

widely

for use in the dog with a gastric fistula.

the drawback

We have modified

of requiring the technique

to used

However,

continuous

manual

control

of Fordtran

and Walsh

of

so that

the amount of alkali infused to maintain the gastric contents at a constant pH is controlled automatically while the gastric contents are pumped continuously through an exterior circuit and reintroduced into the stomach. The exterior circuit permits From

monitoring the

Kingdom. Address Ltd.,

of the pH of the gastric contents

Department reprint

Ware,

Received

requests

Herts., February

United

of

Pharmacology, to Dr.

M. J. Daly,

Glaxo-Allenburys Department

and the introduction

Research

Limited,

of Pharmacology,

Ware,

of alkali

Herts,

Glaxo-Allenburys

United Research

Kingdom.

28,1979,

revised

and accepted April

17,1979.

63 @ Elsevier

North

Holland,

Inc., 1980. Journal of Pharmacological

Methods

3, 63-69 (1980)

0160~%02/80/01006307$02.25

64

M. J. Daly, R. W. Hartley, and R. Stables to maintain

a constant

gastric

pH. The volume

of alkali

a numerical print out and a graphic display. available autotitration equipment in conjunction

added is recorded

both as

The system utilizes commercially with a titration display unit which

we have constructed.

METHODS Apparatus This

apparatus

display

is shown

unit is illustrated

at the level of the gastric round

the exterior

reintroduced contents

is connected ometer

TTT

in Figure

cannula (Gregory shown

into the fundus

in Figure

1 and the design

manifold

(Radiometer

to a pH meter

Type

After

by a roller

holds

62), a titration ABU

end point,

to infuse

the sensory

in the food stream.

PHM

before

leaving the stomach

which

(Radiometer

falls below a predetermined

unit activates the autoburette

of the titration

from the stomach

D) and pumped

GK2401C)

(Radiometer

60) and an autoburette

are removed

1 at the rate of 5 ml set-’

of the stomach.

a perspex

pH electrode

gastric contents control

circuit

pass through

combination

schematically

in Figure 2. Gastric contents

13).

portion

Tube 3mm

hydroxide

pH Meter

I

bore

t Auto -

Flat bed

Titration

Burette

Display Unit

-

Recorder

Titration Controller

Clamp

Silicone rubber tube

FIGURE 1.

of a (Radi-

pH of the

in this case 5.0, the titration

1 mol I-’ sodium

Manifold

B

unit

the

Stomach

7‘

being

the gastric

The electrode

control

When

pump

6mm bore

Schematic diagram of intragastric titration apparatus.

solution

lntragastric Titration in the Dog START

ZERO

Es.R

TNUMB W”EEL SWITCHES

PRINT COMMAND

1

EVENT

COUNl

WUJME COUNT GEAR-BOX AND DISC ASSEMBLY 1

I

SET

I

SLOTTED OPT0

SWITCH

COUNTERS

FIGURE 2.

into the circuit returns

monitored by the titration over predetermined time is recorded (Radiometer A system

similar

the

slotted

burette replicates

B 246d electronic

that rotates

the

of 2,500

photon pulses

50 times via a I:5

coupling

refill,

when

the

burette

drive

counter

step-up

ABU 13 auto-

a light

the burette

incorporated

source

into

By

and a

volume

of one was 2.5

The electronic

in the autoburette,

processing. the phototransistor

goes

volume.

gear box and using

for the displacement

this autoburette.

shaft

recorder

is used to monitor

per total burette

between

series of experiments counter

contents

is continuously

The Radiometer

is generated

sizes can be used with

that of the mechanical

pH of the gastric

schematically in Fig. 2) which records of titrant delivered. This information

information is now suitable for further electronic It is necessary to gate the pulses coming from burette

the

by the autoburette

by the autoburette.

In the present

other

until

and as a bar chart on a fiat-bed

10 slots on this output

a total

volume.

printout

output

disc to interrupt

ml, although

pump

hydroxide

display unit (shown periods the volume

delivered

a disc with

phototransistor,

the

to the Radiometer

of titrant

has a mechanical

mounting

from

of sodium

both as a numerical REC 61).

the volume burette

Circuit diagram of titration display unit.

downstream

to 5.0. The infusion

D.A.C.

LATCHES

a fast reverse

count but the

during mode

autoand

a large number of surplus pulses is generated. The autoburette possesses a “ready” indicating light which is activated at the end of the refill cycle and a signal derived

65

66

M. J. Daly, R. W. Hartley, and R. Stables from

this part of the circuit

autoburette

is coupled

to minimize

the possibility

titration display unit occludes the delivery into the decade

burette.

of titrant

of earth

pulses

from

within

outputs

are transformed

latched

outputs

simultaneously

period

in analogue when

The time

form.

time.

displayed

These

the new count period

circuit.

When

the clock count

is reset to zero, an event

the titrant

counter

becomes

volume

is updated

completion

of latching,

commanded

to print

by one.

the volume the volume

printer

volume

a small

is monitored

can be

settings,

the clock itself

to the output

delay,

sufficient

latches,

and

to ensure

the

are reset to zero and the digital printer

information

displays.

on a flat-bed

1 and 99 by setting up two decades switches feed one side of a digital receives signals from a BCD clock

appearing

the two decades of event count that appear at counters the circuit diagram, the BCD information from the timing decoded to drive 7 segment within a timing period.

and

the

and the

and displayed.

of titrant

is transferred

counters

reset,

until the end of the next time

to the latches

After

on electronic

about the volume

the counters

equal to the switch

count

The

At the end of that time period

are held

easily adjusted to any time in minutes between of binary-coded thumbwheel switches. These comparator network, the other side of which

the

in order

supplies.

are counted

latches,

the delivered

isolator

power

information

on a digital

outputs

is transferred

over which

the two

(BCD)

to bistable

The signal from

valve which, during burette refill, thus preventing back flow of food

the phototransistor decimal

logic.

unit via an optical

between

a predetermined

counter recorder

loops

to give binary-coded

delivered

the gating

display

also controls a solenoid tube from the autoburette,

The

counters

is used to drive

to the titration

at the latch outputs

and

Cl and C2. As shown in clock circuit may also be

This gives an indication

of the elapsed

time

The display unit utilizes a Date1 DPP-7 panel-mounted printer. This printer is available with a variety of print format options, one of which is of the form “.X.X + .X.X.X.X.” By appropriate wiring at the input socket the decimal points and “?” were

removed

to yield a two-decade

event

count

a four-decade titrant volume count. The information at the volume latch output

followed

by a blank

followed

is also fed into a four-decade

by

BCD-

to-analogue converter, the output of which, after processing for gain and offset (amplifiers Al and A2) is fed to the chart recorder. In order to facilitate the matching of the analogue volume-decade

output counters

to the zero

These

are used in conjunction

logue

output

Validation

amplifiers,

and

are provided with

full-scale positions of the recorder, the “zero” and “nine” jamming circuits.

with

the zero

and FSD potentiometers

of the ana-

prior to the start of the experiment.

of the Apparatus

The test meal was boiled ox liver in water (33% w/w) which had been homogenized for 10 min in a blender. In order to provide a standardized stimulus for a series of experiments the test meal was prepared in bulk and then deep frozen in 400 ml aliquots. Prior to experiment an aliquot was thawed, rehomogenized, and the pH adjusted

to 5.0 with

M HCI.

lntragastric Titration in the Dog “Bench”

Testing

The 400 ml test pumped

round

meal was placed in a beaker

the circuit

shown

in Figure

were added to the food and the amount to pH 5.0 end-point

representing

1. Known

the dog stomach

and

of hydrochloric

acid

quantities

of alkali added from the burette

and time

recorded.

Dog Experiments A male beagle dog (13 kg), with into

the most

ments.

Before

water. with

dependent

each experiment

Immediately water

before

at 37°C.

a titanium

part of the whole

the dog was fasted

commencing

Provided

Gregory stomach,

overnight

the experiment,

gastric

contents

were

secretion was less than 25 p mol H+ over the next begun. The test meal was 30 ml homogenized liver adjusted before

to pH 5.0. A small portion the

bung

gastric cannula,

carrying

ensuring

dog was then allowed roller

and gastric circuit

out at weekly

intervals

the

the stomach minimal

experi-

free access to was washed

and spontaneous

30 min, the experiment was per kg bodyweight and was

of this test meal was used to prime the apparatus and delivery

tubes

that the delivery

tube pointed

away from the pylorus.

were switched

was inserted

the gastric

(approx.

in random

order.

intravenously

2 mg kg-‘h-l,

on and left to operate

reduced

to operate

rate of 3 ml min-’

Cimetidine,

with

the extraction

emptying

for the pump

implanted

to eat the rest of the meal at time 0. One minute

pump and titrator

digestion

type D cannula

was used for these

25 ml).

Seven

experiments

30 min

concurrently

The

later the

automatically

to a level

In each experiment

commencing

was infused

contents

in the

saline

until

insufficent

were carried was infused

before

the test

at

meal.

in three of the experiments.

In

these experiments the titration display unit was set to operate on a IO-min cycle. Results were recorded as a numerical print-out and as a graphic display in the form of a bar chart of the type shown

in Figure

3.

RESULTS “Bench” The

Testing

results

summarized

in Table 1 show that the apparatus

acid added to the test

meal as there

expected

and those

titrant

values

point was approximately

was no significant

obtained.

The

time

30 set and was independent

can accurately

difference

required

titrate

between

the

to reach the end-

of the amount

of acid added.

Dog Experiments The which

results

in which

the dog experiments

the results

cimetidine

the control mmol-’

from

compares

obtained

was infused

intravenously

test meal was immediate

at 40 min.

Acid secretion

are shown

in composite

for test meal alone with reaching

at 2 mg kg-‘h-l.

form

similar The

in Figure

3,

experiments response

to

a peak of 0.78 ? 0.06 (mean ? s.e.)

was maintained

for approximately

190 min,

at

which point the major part of the meal had left the stomach. Cimetidine, 2 mg kg-‘h-l, produced significant reductions in acid secretion of 46% (p < 0.01) in respect of peak rate and 70% (p < 0.02) in total output.

67

68

M. 1. Daly, R. W. Hartley, and R. Stables

o

Salim, atrot

m

Cimetttins

(n=4) Zmg kg-‘h

-vn-3)

secntii

Ackt m md

H*/lOmin

+M

M

120

90

350

Test

lbc Tii

Marl

in mins

from tsst

mwl

FIGURE 3. Secretory response of the gastric fistula dog to a test meal during intravenous infusion of saline or cimetidine.

DISCUSSION We have assembled to a test meal which the

meal

manual hanced

a system

for measuring

will run automatically

has left the

stomach.

the gastric

once started

It eliminates

the need

for constant

response 95% of

attention

and

titration. The response to acid secretion is rapid and gastric mixing enby the use of a roller pump which circulates the starting test meal volume

in 75 sec. The low standard errors, generally replicate experiments indicate that the method The

acid secretory

until approximately

use of sodium

hydroxide

instead

less than + 30% of the mean, provides reproducible results.

of sodium

bicarbonate

TABLE 1 Titration Data from “Bench” Testing of IntraGastric Titration Apparatus M MOL

MEAN

HCL

ADDEO TO MEAL

VALUE+

(95%

CONFIDENCE

INTERVAL)

_ M MOL NAOH

REQUIRED

TO NEUTRALIZE MEAL

TIME IN SEC TAKEN TO NEUTRALIZE MEAL

0.25

0.24 (0.18-0.33)

34.5 (77.9-66.3)

0.50

0.54 (0.49-0.59)

35.0 (30.5-40.2)

1.00

1.02 (0.92-1.14)

29.0 (26.8-31.3)

2.00

1.95 (1.88-2.03)

38.3 (34.9-42.1)

t Geometric

mean of 5 titrations.

to neutralize

for the

lntragastric Titration in the Dog acid secreted

eliminates

the generation

release tube in the stomach. of COZ, although to high CO, amount sum

Fordtran

of alkali

of acid

While

injected

less the

this

paper

system

in common

inaccuracies

net acid secretion,

from

salivary,

of the progress

experiment.

recorded

These

The bar chart

Heidenhain

with that described

line recording is continuously

display

due

which

pancreatic,

of the experiment.

over time

periods

data are presented

The is the

biliary,

graphic

display

no further

the

original

titration

method

a much lower pH if uncontrolled, conditions are standardized for Our

results

have shown

dine is effective in reducing at a dose which is effective al., 1975).

Consequently,

drugs and other

and

Walsh

has

control

of the on-

of titrant

delivered

printout

modification

physiological

has some

at the beginning

of the

and as a bar chart.

of the experimental

of Fordtran

is not entirely

The volume

both as a digital

published

our apparatus

adjustable

that are preset

requires

(1978)

dogs which

However,

unit that provides

is a useful,

As with

pouch

in this paper.

in Figure 3, which

intragastric

dog.

base

for a gas generation

if the pH was 6.0 or more.

reflects

secreted

without

that titration

significant

for use with

of a titration

agents.

the need

and acid loss by back diffusion. Carter and Grossman was in preparation,

the advantage

shown

(1973) showed

only became into the stomach

secretion

and obviates

secretions,

of a titration

features

of CO,

may also be more accurate

and Walsh

concentrations

nonparietal details

Titration

results,

in the form

or transformation. (1973),

the

since the gastric

technique

pH would

of

fall to

and this may affect gastric emptying. However, comparative studies with different therapeutic that the histamine

HZ-receptor

antagonist

cimeti-

the secretion of gastric acid in response to a test meal against other secretory stimulants (Brimblecombe et

this method

procedures

can be recommended

on the gastric secretory

It may also be of value,

with

slight modification,

for the evaluation

response

of

to a test meal in the

for clinical

use.

REFERENCES Brimblecombe

RW,

Duncan

mett JC, Ganellin tidine-A

CR,

WAM,

Parsons

non-thiourea

Durant

GJ, Em-

ME (1975) Cime-

Hz-receptor

antagonist.

/ Int Med Res 3: 86-92. Carter

DC,

Grossman

pH on acid secretion evoked

by topical

Physiol281:227-237.

Ml

(1978) Effect

from

Heidenhain

and parenteral

JS, Walsh

rate and buffer ing.

Results

with

duodenal

George

of luminal /

JM (1973) Gastric content

in normal ulcer.

13: 376-383.

acid secretion

of the stomach subjects

after eat-

and in patients

/ C/in invest

JD (1968) Gastric

Dig Dis

pouches

stimulants.

Fordtran

52: 645-657.

acid and motility.

Am j

69