Effect of angiotensin II on blood flow in the transplanted sheep squamous cell carcinoma

Effect of Angiotensin Transplanted Sheep

II on Blood Flow in the Squamous Cell Carcinoma* MARK A. BURTON,

University of Western Australia,

Abstract-The

effects of systemic infusion of angiotensin

in the sheep squamous cell carcinoma after transplantation microspheres.

The ratio of arterially

tissue compared angiotensin

to normal

II. Doses of angiotensin

26 mmHg produced addition,

signtjkant

was

II on the distribution microspheres

measured

II inducing increases

increases

of Surgery, Royal Perth Hospital,

Perth, Australia

of blood flow

to the liver were measured using tracer

introduced radioactive

hepatic parenchyma

BRUCE N. GRAY and ANGELA COLETTI

Department

before

embolizing

in mean arterial

in the embolization

in tumour

and after

ratio from

infusion

of

blood pressure 2.8

to 4.111.

of In

the ratio of microspheres gaining access to the necrotic centres of the tumours compared

to the normal liver tissue significantb internal radiation

increased from

therapy for hepatic metastases,

injection of radioactive

microspheres

1.6 to 2.3: 1. In terms of the technique of

the concurrent infusion of angiotensin II with

would result in a substantially

enhanced radiation

dose to

liver tumours. At the same time the dose to normal tissue can be minimized.

INTRODUCTION METASTATIC hepatic

cancer

most

and

recalcitrant

However,

the

common

malignancy. hepatic

metastases

untreated

7 months

Various

treatment

with minimal

the

the subject

of human

vascularity

treated

to that

therapy

of yttrium-

to become

entrapped

of liver

tumour

isotope

of 0.25 cm

accumulation.

The greatest when

a solid

confine

must

be actively

shunted

publications

administration introduction

have recently

of vasoactive of microspheres

shown

drugs prior into the hepatic

Accepted 1 April 1988. *Supported by the University of Western Medicine Research Committee.

Australia,

resident

tumour

favouring

the

will also to that

We have

further

model. ofthis

tumour

liver.

to the

tissue

This

the effect angiotensin

drugs study

in assess-

after was

transplandesigned

to

vasoconstrictor

II on the distribution tumour

as

examined

for utilization

of the potent

in transplanted

in the sheep

the suitability

cell carcinoma

tation

of mic-

and normal

liver

model.

MATERIALS AND METHODS

tumour Animals

that the

Five

to the artery

Faculty

with generalized

the

squamous

of vasoactive

rospheres

tissue. Several

neova-

[8]. Vasoconstric-

flow response

ing the action

peptide

ben-

radiation

into

tumour

determine

dose is substantially greater in tumour tissue rather than in normal tissue. For this to occur the microspheres

on

results

unreactive

et al. [9] described

epidermal

the suitability

of micro-

therapeutic

the subsequent

not

hyper-

flow.

of the sheep

tissue.

will area

[7] and

metastases

In 1986, Harker

with a mean

which

to the immediate

efit will be obtained

an

bolus

for the liver

with a net blood

blood

introduced

arterial

liver vasculature but

[5, 61. This

tumour

tumour supply. Blood borne microspheres embolize in the tumour tissue in proportion

and exper-

requires

of hepatic

vasoconstriction tissue,

embolization

physiologically

tars act on normal

[ 1, 21.

radiation

therapy

is a pure l3 emitting damage

sculature

of

assessed

described

from the relatively

of the time

been

of clinical

microspheres

penetration

sphere

to normal

[3, 41.

microvasculature

radiation

tumour

in addition

survival

have

but internal

arterially

Yttrium-90

preferential

occurs

for

different

a median

radiation

90 impregnated

prognosis

modalities

been

intrahepatic

forms

causes one of the

from the time of diagnosis

investigation

Internal

tissue

with

success,

has recently imental

in

is little

disease

approx.

is presently

crossbred

merino

sheep

with

an

average

body weight of 42.3 * 5.2 kg (S.D.) were utilized for these experiments. The animals each had a spontaneous tumour occurring on one of either the ear,

of

nose

carcinoma 1373

or vulva. which

The arises

epidermal spontaneously

squamous

cell

in approx.

1374

M.A. Burton, B.N. Gray and A. Coletti

1% of sheep detail

in Australia

ofhealthy

tumour

primary

has

lobes

then

completely

animals

of the liver.

were

described

segments

tissue were transplanted

site from each animal

right

been

et al. [9]. Small

by Harker

in

primary

resected

and

maintained

for

from the

and

after

tumour

was

recovery

the

12 weeks

the second

was then injected.

into both the left and

The

was constant

(1 mms)

prior

to

stopcock

normal min

and

flushed

twice

The infusion

minutes

were

after

sacrificed

the final injection,

the ani-

the

l.tLl.5

g. These

samples

central

portions

of the tumour

15 km

scopic

labelled

with

either

to measure

the implanted

tumour

normal

parenchyma.

hepatic

rospheres

contained

carried

tissue

counter

maintained errors.

The

determine

ensuring to

minimize measured

(T/N) under temic

infusion during

using

one set of labelled

flow

after

II. The of saline,

in

T/N

were present, and

normal

liver.

embolization

the tumour

compared

oxide

was performed exposed.

site at the junction

artery

the junction

and

Gastric

from the hepatic

artery, were polyethylene denal

ligated. catheter

with

distal

with

difference

ratios

under

the tip of the catheter the hepatic

hepatic

artery

artery.

after

between

angiotensin

before

catheters

were

femoral

for infusion

II infusion

t test for paired

generally

of

+ S.D. for

was calculated and

the ratio

of

portions

of

parenchyma

TIN and

the

compared

to those

was

variations

of variation

C/N

measured

observations.

with

This test was

in the percentage

for normal

tissue

samples

infusion.

of saline

II and

the latter

The

first

prior

control

placed

at

injection

the cardiovascular

to angiotensin

of the

second

reactions

throughout

with a mean 26 had

II infusion

population

examined

was

found

responses

There

to the doses ofangiotensin was

From

a total

the five

of 28 tumours

size of 10.7 + 5.3 mm (S.D.).

central

portions

of tumour

in blood

pressure

Ofthese,

necrosis.

mean

This catheter

was

angiotensin II in the sheep was 26.8 + 2.9% each individual control measurement.

into

as a control

the fem-

sheep,

the

and for the

for the measurement

of microspheres

was pulsed into the hepatic artery over 30 s when the pressure was constant for at least 5 min. The angiotensin II was then infused at an increasing dose until the blood pressure was maintained at 25% above the control level. When this pressure

increase

There growing (Fig. 7%.

was an increase edge)

1). The The

induced

T/N ratio

for one tumour T/N ratio

control

The by the

in the T/N ratio

for 27 of the 28 tumours

mean

to

or the introduction

of microspheres.

the experiment. there

not

of the sheep

into

of the

population

initial

divides

introduced artery

The influence

II used

of the animal’s mean systemic blood pressure. At the commencement of each experiment, normal saline was infused and the blood pressure monitored.

the

conditions

and after drug

sheep

At this point

of the microspheres.

angiotensin

and the mean

to the normal

control

were no adverse

A 1 mm (outside diameter) was tied into the gastroduo-

arteries.

former

vessels

the gastroduodenal

with

and

a

to the injec-

the left and right hepatic

vein

of the

activity

Statistics

coefficient

artery

or duodenal

artery,

used for the introduction Similar

rest

specific

in the central

also used to determine

the

anaesthesia

the hepatic

with

the common

oral

the growing

the

microspheres.

halothane-nitrous

of the sheep tion

The

(a) the

of macro-

RESULTS

laparotomy leading

from

(b) from

was

weighing

if areas

of the TIN ratio

Procedure Under

taken

(c) from

was measured,

microsphere

Student’s

the blood

measured

were

tumour,

for determination

The

the sys-

(e.g. cobaltwith

200 samples

(C/N).

tissue

control

approx.

and

animal

to

was measured

associated II was

labelled

after

microspheres

T/N ratio

angiotensin

contrasting

hepatic

and

of angiotensin the infusion

used

embolizing

to normal

conditions

ratio,

the

geometrical

of microspheres

control

size was

were

removed

each of the above liver compartments

was

a 3 channel

the sample

thus

compared

of mic-

Activity

using

constant

tissue

57) while

each sample

activities the ratio

tumour

injection

3 X lo6 microspheres

that

of the

surrounding

Each

samples

necrosis

edge

supplying

the surrounding

10% dextran.

in tissue

Gamma

or tin-l 13

of blood

and

approx.

in heparinized

determined

cobalt-57

the ratio

liver

The liver ofeach

Polystyrene copolymer tracer microspheres (Nentrac, New England Nuclear) with a diameter of used

.O ml/ II was

then

were

0.4 ml of

were 0.6-l

of angiotensin

Radioactive microspheres

into

the catheter

with

rates

and

fixed in 10% formalin. divided

of microspheres

each injection

the concentration

20 kg/ml. Fifteen mals

experimentation.

were

saline.

population

After

above

(tumour examined

dropped

by

for all tumours

was 2.8:1 (2.5 S.D.) which was increased after the angiotensin II infusion to 4.4:1 (3.4 S.D.). The average

increase

drug induced P < 0.001. The C/N

was

106 * 89%

change ratio

(central

which

from

was

necrosis

control

significant

to normal

to at

tissue)

increased in 22 of the 26 tumours from a control of 1.6:l (2.5 S.D.) to 2.3:1 (3.3 S.D.) after the angiotensin II (Fig. 2). This was equivalent to

Angiotensin II and Tumour Blood Flow Angiotensin strictor

1375

II as a potent

[ 1 l] will cause

hepatic

arterial

vasocon-

generalized

vessel

constric-

tion in the normal tissue but not in tumour tissue, resulting in a net favouring of blood flow to tumour tissue.

Blood

borne

our the tumour

microspheres

vasculature

tion with angiotensin The

efficacy

dependent liver

Angiotensin II

Saline

Fig.l. Changes in the tumour growing edge to normal liver tissue ratio (T/N) in sheep after the infusion of angiotensin II. Boxes indicate group means.

to tumour

tissue.

We

ered

the

unaffected infusion reported

hepatic

vasculature,

of angiotensin

II.

after

large

of the tumour

a similar

rabbits

model

of TIN and directly

response

systemic

animal

tissue

compared

to the

have

in rats and

II

[5] but

this

the determination

infusion

of the drug

artery.

II has been used in renal

pharmacoangiography flow in humans

the

previously

in tumours

after

deliv-

following

We

has allowed

GIN ratios

significant

of tumour

angiotensin

into the hepatic

Angiotensin

a

edge

is

than to normal

of microspheres

growing

to the centre

therapy of radioactive

described

in the number

and

radiation delivery

tissue rather

have

improvement to both

fav-

used in conjunc-

II.

of internal

on the preferential

microspheres

will therefore

when

to highlight [ 12, 131. More

and muscle

tumour

recently

blood

et

Sasaki

al. [14] have with

advocated the use of angiotensin II intrahepatic arterial infusion chemotherapy

to provide

better

drugs

turnours.

to

of 1.5:1 degree Angiotensin II

Saline

sheep after infusion of angiotensin II. Boxes indicategroup

in

means.

with the results this model

significant

at

P < 0.01. The samples

coefficient

of normal

liver was determined

ure of the homogeneity rospheres

measurement

decreased

after

39.4 * 13.4%. sheep,

the

of the mic-

The mean

coefficient

was 52.4 + 29.3%

infusion

The

for the as a meas-

of distribution

on embolization.

the control

of variation

of angiotensin

decrease,

was not statistically

in two

for

which

of the

anatomically tors

but

function.

vessels under

they They

have

do not

retain

do not have

shown

be exerted through of the surrounding

of radioactive

normal

rospheres

within

the

five

being

physiological

the ability

to regulate and they do [lo]. Because

physiological in tumour

the vasoactive normal hepatic

inert, a tissue can

manipulation vasculature.

tumour

growth,

bution.

The

no significant

fraction

coefficients

influence

lations

rather

than

of the micby the

a relatively with

even

for the normal

low distri-

liver

com-

reported for rats and of angiotensin II had

on the distribution

in the normal

for the occurrence

of microspheres

not affected

of liver

described

of variation,

synonymous

of the microspheres the potential

was

the

disproportionate

microspheres,

liver

In this but still

with angioten-

the total to receive

with

changes

centre.

just the growing edge. The homogeneity of the distribution

coefficient

fac-

though

and necrosis,

significantly

that

coefficient

to develop

by angiogenetic

blood flow, direction or capacitance not have a normal neural innervation these vessels are relatively degree of blood flow control

numbers

means be induced

The

favourably

to measure

for further

pared favourably with those rabbits [4, 151. The infusion

been

stimulation

This

a mean

scintigraphy.

to the tumour

also increased

can

from

for the sheep,

avascularity

percentage

DISCUSSION Neoplastic

supply

to

II

(P > 0.05).

significant

tissue

hepatic

recorded

the potential

sin II.

percentage

significant

in humans

in the TIN ratio agrees

of relative

C/Nratio

described

it was also possible

in the blood with

of 84 k 131%,

increase

using

of increase

region an average

to 4.3:1

of chemotherapeutic

They

in the TIN ratio

increases

Fig. 2. Changes in the tumour centre to normal liver tissue rutio (C/N)

accessibility

patterns

liver tissue. of local

and therefore

Thus

accumu-

radiation

was

by the vasoconstrictor.

CONCLUSION We would conclude that the vasoconstrictive effects of infusion of angiotensin II concurrent with the injection

of radioactive

microspheres

into

the

I376

M.A.

Burton, B.N.

hepatic artery will provide preferential delivery of the microspheres to tumour tissue. The increase in the net proportion of blood supply to the tumour tissue provides greater access to cytotoxic agents to both the central portions of the tumour and the

Gray and A. Coletti

growing edge of the tumour, while relatively sparing the normal tissue. The transplantable sheep squamous cell carcinoma provides an excellent model for tumour blood flow studies in a preparation ofsimilar size and morphology to the human situation.

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