Selective Abolition Of Ca-Dependent Responses Of Smooth And Cardiac Muscles By Flunarizine

SELECTIVE

ABOLITION

SMOOTH

AND

OF

Ca-DEPENDENT

CARDIAC

*Koichi

RESPONSES

MUSCLES

NAKAYAMA

and

BY

Yutaka

OF

FLUNARIZINE

KASUYA

Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, University of Tokyo, Hongo 7-3-1, Tokyo 113, Japan Accepted

Abstract-The inhibitory effect compared with that of verapamil at a small dose shifted traction due to electric reduced the maximum

June

2, 1980

of flunarizine on in isolated smooth

the Ca-dependent responses was and cardiac muscles. Flunarizine

to the right the dose-response curve for Ca2+ of the phasic con stimuli in rabbit basilar strips, while in a large dose, flunarizine tension and slope of the dose-response curve. The high K-

induced vasoconstriction of the However, the action of flunarizine

rabbit basilar artery was inhibited by flunarizine. was about 30 times slower than findings with verap

amil. The spontaneous activity of the rat portal vein was less susceptible to flunarizine, whereas that of rat uterus was completely inhibited by flunarizine. Flunarizine possessed moderate negative chronotropic and inotropic actions on the right atria and papillary muscles of the rabbit. tagonizing Ca-dependent

Our experiments indicate that flunarizine is selective in an contraction of the rabbit basilar artery, probably by blockade

of the transmembrane Ca. It is also possible that the slow onset of action and non surmountable antagonism produced by flunarizine is due to other pharmacological interventions such as delayed effect of metabolites, on the cell membrane of vascular smooth muscles.

Flunarizine,

possesses

vasodilating

vascular

beds (2) and antagonizes

induced

contractions

with cerebral

with transmembrane

herent

between myogenic

classified various cardiac

properties

in cerebral

the action of various

or tight

or peripheral

Clinically

vascular

augmented activity

it appears

Ca2+ influx by vasoconstrictor

in vascular

smooth

drugs with antagonistic

muscles and regarded

muscles

properties

flunarizine

of vascular

Moreover,

agents

(4, 5).

and its congener

contractile

responses

peripheral

and calcium is used in the

It has been sug

tissues by interfering that flunarizine

dis

and that due to the in

Godfraind

to the function

flunarizine

other

substances

diseases (7-10).

selectively acts on the cell membrane Ca2+ influx (2, 4, 5, 11).

binding

piperazine

(1) and

vasoactive

in vivo as well as in vitro (2-6).

of patients

gested that flunarizine

sociates

action

(E)-1-[bis(4-fluorophenyl)methyl]-4-(3-phenyl-2-propenyl)

dihydrochloride,

treatment

stabilizing

and Morel

(12)

of Ca2+ in smooth

and

cinnarizine

as selective

blockers

of Ca2+ influx. In previous arteries

studies,

the

of rabbit

(14-16) to electric stimuli and high concentrations

be strongly

dependent

were depressed * Present University,

on extracellular

following

address:

Department

Sagamiko,

Ca2+ concentrations.

Ca2+ withdrawal,

Kanagawa

of

or blockade

Pharmacology 199-01,

Japan.

, Faculty

coronary

of potassium

(13) and cerebral ions were shown to

These contractile

of transmembrane

of

Pharmaceutical

responses

Ca2+ influx by

Sciences,

Teikyo

Ca-antagonistic dition

drugs

of Ca2+ in small The

present

study

such

as verapamil,

concentrations was thus

nifedipine,

restored

undertaken

drugs,

bencyclane,

to compare

of several

Ca-antagonistic

responses

of the cerebral

artery

and other

regarding

the inhibitory

action

of flunarizine

whereas

subsequent

ad

the contractions.

particularly

the effects

veraparnil,

smooth

muscles.

and verapamil

on

the

of flunarizine

with

Ca-dependent

We also compared on cardiac

effects

contractile the specificity

and vascular

tissues.

MATERIALS AND METHODS 1. 1-1.

Isolated vascular and uterine preparations Rabbit basilar artery Electric field stimulation:

Albino rabbits of both sexes, weighing 1.8 to 3 kg were

anesthetized with pentobarbital (30 mg/ kg i.v.) and exsanguinated from the common carotid arteries.

The basilar artery was excised and carefully cleaned from connective tissue, under

a dissection microscope, and then cut into helical strips.

The average length and wet weight

of the basilar strips were 10 mm and 0.3 mg, respectively (N=130).

The preparations were

mounted in an organ bath containing 100 inl Tyrode solution (molar concentration: NaCl: 158.3; KC1: 4; CaCl2: 2; MgCl2: 1.05; NaHCO3: 10; NaH2PO4: 0.42; glucose: 5.6 mM) which was bubbled with 97 ;' 02 and 3'1 CO, to give a pH of 7.35 at a temperature of 35'C. The basilar strip in the organ bath was allowed to equilibrate for at least 2 hr before the actual experiment was started. Electric field stimulation by rectangular alternating pulses of 10 Hz, 10 V/cm, and stimulus period of 8 sec was intermittently applied at 5 min intervals along the long axis of the muscle preparation, by means of two vertical platinum plate electrodes (23 x 10 mm). The distance between the two electrodes was 10 mm and the muscle strip was placed in the middle.

To secure a constant level of the developed tension and the basal tone during

several hours observation period, the initial length, as the starting point of each experiment, was defined as the length of the unloaded preparations (=100%) at which tension was not induced by electric stimulation.

Then, the muscle strip was stretched stepwise about 150

related to the initial length of 100% and allowed to slowly relax for 30-60 min.

When the

resting tension had reached a constant level, the preparation was again stimulated and the developed active tension was measured.

The graded elongation of the muscle preparations

by the standard procedure was as described in detail elsewhere (13). The assessment of Ca-antagonism was carried out with the following procedures. After an equilibration period of 2 hr the bathing fluid was replaced by 0.05 mM CaC12con taining Tyrode solution.

Then, phasic contractions of the basilar strips were produced by

addition of cumulative concentrations of CaCl2 (0.1-64 mM) to the organ bath until the force of contraction was reached a maximum. contractile response was considered as 100%. fluid every 10 min, then followed.

The maximum amplitude of the phasic A 30 min washout with a change of bathing

Subsequently, flunarizine or verapamil was added to

the organ bath.

After a 40 mnin incubation period, the dose-response curve for CaC12 was

again produced.

The pA2 and pD'2 were calculated according to the definition by Arun

lakshana

and Schild (17).

K+-Contracture: substituting

Tyrode solution

NaCI with an equimolar

were depolarized 40; CaCh:

with K+-rich

with increased amount

produce

a maximum

tension

between

of KCI.

Tyrode solution

2; MgCl2: 1.05; NaHCO3: contracture.

was prepared

The electrically-driven

(molar

10; NaH2PO4:

concentration:

0.42; glucose:

basilar strips

NaCI:

122.3; KCI;

5.6 mM) for 60 min to

phasic

contractions,

to the bathing

solution

steady-state

as induced

by electric

until an equilibrium

concentration

in the medium was increased by adding CaCI2 to the solution.

of the basal tone was obtained.

The Ca"

Portal vein and uterus of the rat Longitudinal

about

250 g.

strips of the portal

vein were obtained

Uterine

horns were obtained

excised,

hr later, the animals

cleaned,

subserosal

and a midline

connective

were about

7.35 for at least

were 11 mm and

dipropionate,

incision made.

tissue, longitudinal

smooth

muscle,

at a temperature

the experiments.

The effect of drugs on the spontaneous

The passive

myogenic activity

Isometric

contraction

\,,,,as recorded

in the experiments

muscle and rig ht atrial preparations

Albino rabbits of either sex weighing

in Tyrode solution papillary

muscles

removed.

of 35'C

and a p1-I of

or initial

tensions

on the smooth

of the muscle

of 7.35 at a temperature

preparations

of 30-'C.

7 to 8 mm in length

were mounted

The solution

of

muscle (TR-10,

of the rabbit

of 0.4 to 0.6 mm in diameter,

100 ml Tyrode solution.

of

respectively.

until a steadystate

was carried

out

of 22'C.

The

O2 and 3 ° CO, at a room temperature

to I mg taken from the right ventricle

in

I to 2 kg were sacrificed by a blow on the neck and

Dissection

aerated with 97

muscle

was mounted

preparations mentioned above was recorded using a n cchanoelectric transducer Tokyo Koki-Schenk) and displayed on a pen-writing recorder (B-261, Rikadenki).

the hearts immediately

day.

peritoneum,

and part of the circular Each preparation

70 mg and 300 mg were applied to the portal vein and the uterine preparation,

Papillary

250 g

i.p., on the previous

The muscle strips containing

in Tyrode solution

I hr before starting

the activity was observed.

about

were sacrificed by a blow on the neck, both uterine horns

10 lion in length and 15 mg in wet weight.

an organ bath and equilibrated

rats weighing

from Wister rats weighing

which had been given 0.2 mg/kg of diethylstilbesterol Twenty-four

from female Wister

The mean length and wet weight of 15 muscle preparations

5.4 mg, respectively.

2.

stimuli.

and the effect on the K+-contracture

was observed

1-2.

by

The basal tone was defined as a steady state of resting

the two successive

Drugs were added cumulatively

K+ concentrations

was aerated

and wet weight of 0.8

vertically in an organ bath containing with 3 ° CO2 and 97'/

A resting tension of about

02 to give a pH

400 mg was applied to each

papillary muscle. Electric stimulation was from a electronic stimulator (SEN-7103, Nihon Kohden). Square wave pulses of I cosec duration and twice the threshold in intensity were delivered

to the tissue through

isometrically

platinum

using a mechanoeleciric

electrodes. transducer

mum rate of rise in tension development differentiator

(ED-6000,

rise were displayed

Nihon

(dT/dt)

Kohden).

on a pen-writing

recorder

The tension development (TR-10,

Tokyo

was measured

The isometric (WI-640G,

Koki-Schenk).

was measured The maxi

by means of an active circuit

tension

and maximum

Nil-ion Kohden).

rate

of

Right atria including the sinus node were carefully excised and mounted in an organ bath.

The wet weight of 15 preparations was 10 to 15 mg.

solution was 30°C and a pH of 7.35.

The temperature of Tyrode

The spontaneous electrical activity was monitored

by bipolar platinum electrodes attached to the surface of the preparation.

The shape of

the electrogram was rectified and fed into a biological amplifier (AB-620G, Nihon Kohden). The rate of spontaneous activity of the right atrium was recorded by means of a digital cardiotachograph

(AT-600G, Nihon Kohden) triggered with the electrogram.

The effect of each concentration

of drugs on contraction of papillary muscle and the

rate of beating right atrium was observed for 40 min. Drugs:

The following drugs were used: Flunarizine dihydrochloride (Janssen, Belgium;

Kyowa Hakko, Japan) was dissolved in 0.01 M tartaric acid, cinnarizine (Janssen, Belgium) in 0.01 M tartaric acid mixed with 0.04 N hydrochloride.

Nifedipine (Bayer, West Germany)

was dissolved in LuteroPR, and used under a sodium lamp.

Verapamil hydrochloride

(Knoll, West Germany; Eisai, Japan), bencyclane fumarate (Thiemann, West Germany; Sumitomo Kagaku, Japan), pindolol (Sandoz Yakuhin, Japan), phentolamine mesylate (CIBA-Geigy, Japan), atropine sulfate (Tokyo Kasei, Japan) and tetrodotoxin (Sankyo, Japan) were dissolved in aqueous solution. Drugs were added directly to the organ bath and expressed in molar concentration. Statistical evaluation:

Results were given as mean ±S.E. ED50-values were determined

by probit analysis (18). Significant differences (p<0.05

or 0.01) between means were

evaluated by Student's t-test. RESULTS 1. 1.1.

Vascular and uterine smooth muscles Rabbit basilar artery Electric field stimulation :

Phasic contractile responses of the basilar arteries to electric

stimuli of rectangular alternating pulses of 10 V/cm, 10 Hz, stimulus period of 8 sec and 5 min interval were highly dependent on the Ca2+ concentration modulated by pindolol (2 x 10-6-4 x 10-6 M), phentolamine

in the medium, but were not mesylate (4 x 10-6-10-5 M),

atropine sulfate (5 x 10-1-2 x 10-6 M) or tetrodotoxin (3 x 10-' M).

Figure 1 shows the

contractile reactivity of three basilar strips to varying external Ca2+ concentrations and to verapamil.

The maximum tension of a basilar strip developed with a Ca2+ concentration

of 8 to 10 mM.

Further increase in Ca2+ reduced the amplitude of the isometric con

traction even when electric stimuli of 30 V/cm were applied.

Conversely, the contractility

declined in a Ca2+-deficient medium, until at an extracellular Call concentration of less than 0.05 mM, the mechanical responses disappeared.

In another preparation, the amplitude

of the isometric tension was suppressed by 1.2 x 10-6 M verapamil, while the response was promptly restored when the concentration of Ca2+ in the medium was doubled from 2 to 4 mM. Figure 2 illustrates dose-response curves for Ca2+ before and after the administration of flunarizine and verapamil.

With a concentration of up to 2.2 x 10-6 M of flunarizine,

the

dose-response

parallel

shift

flunarizine

for

to the right.

in and

flunarizine. in a large

slope the The

dose

and

slope

such

pA2 value over

maximum

of the

pD'2

Ca 2+ in the

The

at a concentration

reduction stimuli

curves

value

electrically

for flunarizine

6.6 x 10-6 effect.

M on

The

dose-response

curve

for

was

as 2.0 x 10-5

flunarizine M,

on

stimulated

the

was

the

was

phasic

6.4.

dose-response

maximum

5.4.

basilar

tension

reduced The

with

inhibitory

contraction

arteries

However, curve

showed

a

the effect

of

comprised

developed

by

increasing effect

following

electric doses

of electric

a

of

verapamil stimuli,

FIG. 1. Phasic contractile responses of 3 electrically stimulated rabbit basilar strips to increasing in Ca 2+ concentration in the medium (Panel A), withdrawal of Ca2+ (Panel B) and administration of verapamil (Panel C). Addition of extra Ca2+ 4 mM to the bathing solution promptly restored the contraction of a basilar preparation (Panel C). Electric stimulation was carried out at 5 min intervals with rectangular alternating pulses of 10 V/cm, 10 Hz, and stimulus period of 8 sec.

FiG. 2. Dose-response curves for Ca2+ on the amplitude of the phasic contraction produced by electric stimuli in the rabbit basilar artery. Control dose-response curve for Ca2+ represents the mean of 36 experiments. The phasic contraction due to electric stimuli per cross-section area of the basilar preparation augmented by 10 mM Ca2+ in Tyrode solution was (6.5=0.6) x 10-4 dyne/cm2 (mean±S.E., N=36), calculated according to the method of Herlihy and Murphy (19). Each of curves shows the mean of 6 to 10 experiments after the incubation of either flunarizine or verapamil for 40 min. The maximum amplitude of phasic con traction measured on control strips in Tyrode solution containing 10 mM Ca' is put as 100% on the ordinate.

was antagonized verapamil restored

by increasing

was 5.0.

The inhibitory

by repeated

KI-Contracture:

Cal I concentrations

washings

in the medium.

effects of both flunarizine

during

The pA2 value for

and verapamil

were partially

30 min.

When the K+ concentration

in the medium was increased from 4 mM

to 40 mM, the basal tone was augmented until the basilar strip exhibited the so-called the "K+ -contracture" which lasted for over 5 hr . The basal tone per cross-section area aug mented by 40 mM K+, calculated was 20.6-'-3.4

according

dyne/cm2 (mean_S.E.,

were spontaneous to superimposed

miniature phasic

contractions.

contractions

to the procedure

N=70).

of Herlihy

Accompanying

Additional

of increasing

electric strength

and Murphy

the augmented stimuli

simultaneously

in the concentration

between 8 and 20 mM K+, while above 32 mM K+ the amplitude

(19)

basal tone led range

of these phasic responses

decreased. Figure

3 shows

an example

of the

inhibitory

effect

FIG. 3. Increase in basal tone and augmentation electric stimuli produced by K--rich Tyrode strip. Suppressive effect of flunarizine on added to the bathing fluid partially restored

of flunarizine

on

K+-induced

of phasic mechanical responses to solution (40 mM k"'_+)in a basilar the K+-con tract ure. Extra Call the contractile responses.

FIG. 4. Suppression of the K' -contracture of electrically stimulated basilar strips of the rabbit by various drugs. Degree of relaxation obtained is expressed on the ordinate as percent inhibition of peak tension just before addition of drugs. Each point represents the mean of 5 to 8 experiments with standard error.

vaso

constriction

of a rabbit

and on the

phasic

basilar strip.

contractions

2.2,1< 10-' M of flunarizine

The inhibitory

of the basilar

proceeded

preparation

slowly and reached

The solvents that were used to dissolve flunarizine, on the K+-contracture. of the augmented nifedipine

Figure 4 illustrates

following

a maximum

cinnarizine,

dose-response

and bencyclane.

Among

5 drugs tested,

and long-lasting

and nifedipine

at each dose showed

the Cal+ concentration the K+-contracture

in the solution was partially

a rapid onset

reached

a maximum

(ED50

1.1 x 10-s M), verapamil

cinnarizine 1.2.

(ED50

2.9 ;:10-a

(ED50 2.0 x 10-' M) and bencyclane

inhibition verapamil,

and cinnarizine

showed

a

short effect.

and the inhibitory

within 5 min.

A comparison

of 5 drugs on the basis of ED50 values showed the following

cinnarizine,

of action

of

90 min.

had no effect

had a relatively

up to 8 mM, the inhibitory

compensated.

administration after about

or nifedipine

flunarizine

effect, while bencyclane

effect of both drugs on the K+-contracture

basal tone

curves for percentage

basal tone in the rabbit basilar strips by flunarizine,

slow onset of action Verapamil

effects on the augmented

By increasing

effect of these 5 drugs on of the inhibitory

order of potency;

M), flunarizine

(ED50

activity nifedipine

1.2 x 10-7 M),

(ED50 2.6 x 10-6 M).

Portal vein and uterus of the rat In the control

taneous 15 mg. myogenic

phasic contractions

corresponding

activity of the rat portal vein. the K+-contracture,

the rat portal vein.

inhibition

the portal vein at the preload

Figure 5 shows the comparison

pletely blocked

tractions

period,

between

to 3 to 4/min and a developed of the effects of flunarizine Flunarizine

by 40 to 60',/.

tension of 10 to

and verapamil

the myogenic

the rate and amplitude

There was no statistical

the rate and the amplitude

a rate of spon

on the

in a dose of 2.2 x 10-s M which com

was less effective in inhibiting

At 2.2 x 10-5 M flunarizine,

were inhibited

of 70 mg showed

of the spontaneous

activity

of spontaneous

difference

of

con

in the percent

contractions

of the rat

FIG. 5. A pair of typical experiments on the isolated portal vein and uterus obtained from the same rat. The spontaneous myogenic activity of the rat portal vein was observed after 30 min administration of each dose of flunarizine. E.S.: Electric stimulation with rectangular alternating pulses of 10 `Jjcm, 10 Hz, stimulus duration of 1 sec each time and 3 min interval. Muscle wet weight: 5.6 nmg(portal vein), 12 mg (uterus).

FIG. 6. Comparison of the potencies of flunarizine and verapamil in inhibiting the amplitude 0-0 and the rate 0-0 of spontaneous contraction in the rat portal vein. Percent inhibition of the control is expressed on the ordinate. Each point represents of the mean of 6 experiments with standard error.

portal vein treated the spontaneous Figure

with each concentration

contraction

6 shows examples

from the same rat. taneous

from

7 experiments

Here flunarizine

and verapamil.

on portal

On the contrary,

abolished

vein and uterine

by flunarizine. muscle

in a dose as low as 2.2 x 10-8 M suppressed

activity of the rat uterine muscle, whereas electric stimuli of rectangular

pulses of 10 Hz, 10 V/cm, a stimulus period hand,

of flunarizine

of the rat uterine muscle was completely

verapamil

at 10-s M blocked

of 1 sec evoked the contraction.

the myogenic

activity

of both portal

isolated the spon

alternating On the other

vein and uterine

muscle within 30 min.

2.

Papillary muscle and right atrium of the rabbit The control values of peak developed tension of the papillary muscles at a stimulus

frequency of 1 Hz and the spontaneous rate of the right atrial preparations were 1.0+0.2 g (N=20) and 122±16 beats/min (N=15). cumulative increases in the concentrations

Figure 7 depicts the comparative effects of of flunarizine and verapamil on the isometric

contraction in papillary muscles and the rate of spontaneous activity of right atria] pre parations.

Flunarizine produced a moderate inhibition in the spontaneous rate of right

FIG. 7. Comparison of the potencies of flunarizine and verapamil in inhibiting isometric tension of papillary muscles (P.M.) and spontaneous rate of right atria (R.A.) isolated from rabbits. Percent inhibition of spontaneous rate of right atria is statistically different from that of isometric tension of papillary muscles (*p<0.05; **p <0 .01).

TABLE1. Comparison of the relaxing action on the K+-contracture of the rabbit basilar artery (1) with the inhibition of spontaneous rate of the rat portal vein (2) and with the inihibition of isometric tension of the rabbit papillary muscle (3)

atria,

as

observed

in electrically

difference

between

expressed

as percent

Table on

the

the

I summarizes

force

of

of the

the

comparison basilar

the

of the

the responses

of the three

rabbit

basilar

and

of inhibitory artery,

and

there

effects

effects

myogenic

papillary

muscle.

preparations,

while

different

muscles

chronotropic

was

of

no

statistical

flunarizine,

when

control.

of the

K+-contracture

papillary

inotropic

inhibition

K+-contracture

contractile

stimulated

negative

of flunarizine

activity

of the

Flunarizine verapamil

rat

and

selectively was

verapamil

portal

vein

depressed

equipotent

and the

in inhibiting

preparations.

DISCUSSION The present results demonstrate

that flunarizine

is a selective inhibitor

of smooth muscles

and cardiac tissues. The contractility

of smooth

also high concentrations is required

of contractile

of Ca 2+ by flunarizine

drug acted as a non-competitive that the inhibitory

membrane

bindings

by washing

of cinnarizine,

of rat aortae.

Thus,

manner.

However,

the kinetics

nifedipine,

verapamil

having a gradual

cinnarizine

supply of Ca2+ which stimulated

basilar strips , was competitive, while this

onset and a prolonged

Godfraind

occurred

that flunarizine

of the rabbit basilar smooth

depressed

the

K+-contracture

and bencyclane.

The onset of action

at high concentrations muscles and antagonizes

of

the

of flunarizine

with drugs of the nifedipine

of

that the

at the level of plasma

of relaxing effects of these drugs proved to be different

was 10 to 30 times slower compared

duration

and Morel (12) indicated

of flunarizine,

it seems probable

Ca2+, in a non-competitive

In electrically

stimuli (13) but

when a large dose was given. It has been reported

a congener

membrane

and

elements.

(2, 4, 5).

binds tightly to the plasma

Flunarizine

by not only electric

in low concentrations

antagonist

effect of flunarizine,

action, was not reversed saturable

depolarized

of K+ (20-22) depends on the transmembrane

for the activation

the antagonism

muscles

or verapamil

basilar

strips.

from those of and cinnarizine types.

Thus,

it seems possible that other pharmacological interventions such as a delayed effect of me tabolites or a membrane-stabilizing action are involved in the slow onset of relaxing effect of both flunarizine and cinnarizine. Flunarizine was less effective in depressing the spontaneous activity of the portal vein than in depressing the contractility of the electrically stimulated basilar artery.

On the

other hand, this drug inhibited the spontaneous activity of the rat uterine muscle.

The

spontaneous contractions of both portal vein and uterine muscle of the rat are dependent on extracellular Ca2+ (23-25).

It has been suggested that flunarizine specifically inhibited

increase in the availability of activator Call due to exogenous triggering of the vascular smooth muscle cells, but did not interfere with the potency in producing myogenic activity (4, 5). Furthermore, there may be differences between portal vein and uterine muscle regarding the mechanism of spontaneous activities. The present experiments

also revealed that flunarizine showed moderate negative

inotropic and chronotropic actions on cardiac tissues.

Taira et al. (26) and Himori et al.

(27) compared the effects of various Ca-antagonistic drugs such as nifedipine, verapamil, diltiazem and SKF-24260 on coronary vasodilation and the contractile force of the ventricular muscle by using excised canine papillary muscle preparations cross-circulated with blood from a donor dog.

They found that the dose ratio of each drug determined on the weight

basis in producing a 100% increase in coronary blood flow rate and a 50% decrease in developed tension of the papillary muscle was no more than 1:10.

In the present experi

ments, the dose ratio of flunarizine in inhibiting K+-contracture of the basilar artery and isometric contraction of the papillary muscle was over 1:600 when ED50 values were com pared, whereas that of verapamil was 1:13 (Tablet). Although there are differences between our experiments and those of forementioned authors, in animal species, vascular beds or methods, at least in comparison with verapamil, flunarizine has a highly selective effect on arterial blood vessels because the coronary and basilar arteries isolated from rabbits are equally susceptible to a variety of Ca-antagonists (15). There are some discrepancies among investigators regarding the definition of Ca antagonistic drugs.

According to the criteria proposed by Fleckenstein (24), the mode of

action of Ca-antagonistic drugs such as verapamil, nifedipine, bencyclane etc., is in principle uncoupling of excitation-contraction in both cardiac and smooth muscles. tissues, does not satisfy the criteria.

process by blocking transmembrane

supply of Ca2+

Evidently, flunarizine, a weak inhibitor in cardiac On the other hand, this drug was classified into the

category of a selective blocker of Ca2+ influx (12). In addition, flunarizine was a decoupler of pharmacological receptor-response

because it blocked the extracellular Ca2+-dependent

component of contraction by norepinephrine in rat aorta, whereas verapamil was a weak inhibitor of this action (28). The antagonistic properties of flunarizine on the Ca-dependent responses in several smooth muscle preparations

were qualitatively

different from those of drugs of the nifedipine or verapamil types.

and quantitatively

Thus, the terms of Ca

antagonist or Ca-blocker cannot be used in the same sense to explain the actions of flunarizine and verapamil on vascular smooth muscles.

Recently induced

De Clerk et al. (29) demonstrated

hyperviscosity

membrane.

Godfraind

induced relaxation

of blood, probably

in elucidating attempting

in aorta

effect demonstrated

properties

of flunarizine

to treat cerebral

suppressed

Ca2+ influx through potentiated

the ischemia red blood cell

the isoprenaline

of the aged rat.

organ specific vasodilation,

Acknowledgement:

by inhibiting

flunarizine

(30) found that a low dose of flunarizine

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that

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Flunarizine

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Hakko Co., Ltd.

REFERENCES

1) TOYODA,M., TAKAGI,S., SEKI,T., TAKEOKA,T. ANDGOTOH,F.: Effect of a new vasodilator (Flunarizine) on the cerebral circulation. J. -Neurological Sci. 25, 371-375 (1975) 2) VANNUETEN,J.M. ANDJANSSEN,P.A.J.: Comparative Study of the effects of flunarizine and cinnarizine on smooth muscles and cardiac tissues. Arch. int. Pharmacodyn. 204, 37-55 (1973) 3) VANNUETEN,J.M.: Vasodilation or inhibition of peripheral vasoconstriction? Mechanisms of Vasodilation, Edited by VANHOUTTE, P.M. AND LEUSEN,I., p. 137-143, S. Karger, Basel (1978) 4) VAN NUETEN,J.M., VAN BEEK,J AND JANSSEN,P.A.J.: Effect of flunarizine on calcium induced responses of peripheral vascular smooth muscle. Arch. int. Pharmacodyn. 232, 42-52 (1978) 5) VANNUETEN,J.M., VANBEEK,J. ANDJANSSEN,P.A.J.: The vascular effects of flunarizine as compared with those of.other clinically used vasoactive substances. Arzneinr.-Forsch. 28, 2082-2087 (1978) 6) VANBEEK,J. AND VANNUETEN,J.M.: Specific properties of flunarizine as Ca++-antagonist in vascular smooth muscle. 3rd Int. Sym. on Vascular Neuroe fector Mechanisms, Preposters, p. 68-69, Louvain-en-Woliiwe (1978) 7) VERHAEGEN, H., ROELS,V., ADRIANSEN, H., BRUGMANS, J., DE COCK,W., DONY, J., JAGENEAN, A. ANDSCHUERMANS, V.: The arteriolar effects of cinnarizine and flunarizine. Angiology 25, 261-278 (1974) 8) DoMSCHKY,K., NELSON, M., DAMMHAYN,B. AND TERJUNG, E.: Flunarizin bei Patienten mit zerebraler and peripherer Mangeldurchblutung. Med. Welt 28, 1062-1064 (1977) 9) SCHETZ,J., BOSTOEN,H., CLEMENT,D., FORNHOFF,M., HAERENS,A., ROEKAERTS, P. AND STAESSEN,A.J.: Flunarizine in chronic obstructive peripheral arterial disease: A placebo-controlled, double-blind, randomized niulticentre trial. Curr. Ther. Res. 23, 121-130 (1978) 10) STAESSEN,A.J.: Treatment of circulatory disturbances with flunarizine and cinnarizine. A multicenter, double-blind and placebo-controlled evaluation. VASA 6, 59-71 (1977) 11) OOSTERVLLD, W.J.: Vestibular pharmacology of flunarizine compared to that of cinnarizine. Pract. otorhino-laryrg. 36, 157-164 (1974) 12) GODERAIND,T. AND MOREL,N.: Inhibitors of calcium influx. Mechanisms of Vasodilation, Edited by VANHOUTTE,P.M. AND LEUSEN,I., p. 144-151, S. Karger, Basel (1978) 13) NAKAYAMA, K., FLECKENSTEIN, A., BYON, Y.K. ANDFLECKENSTEIN-GRUN, G.: Fundamental physiology of coronary smooth musculature from extramural stem arteries of pigs and rabbits. (electric excitability, tension development, influence of Ca, Mg, H and K ions). Europ. J. Cardiol. 8, 319-335 (1978) 14) NAKAYAMA,K., FLECKENSTEIN, A., BYON, Y.K., KATO, H. AND KASUYA, Y.: Calcium dependent stretch activation of basilar, coronary and renal arteries. 7th Int. Congr. Pharmacol. Sci., Abstracts No. 93 (1978) 15) NAKAYAMA,K., FLECKENSTEIN-GRON, G., BYON, Y.K. AND FLECKENSTEIN, A.: Opposite effects of cardiac glycosides and Ca-antagonistic compounds on vascular smooth

16)

17) 18) 19) 20) 21)

22) 23)

24) 25)

26)

27)

28)

29)

30)

muscle contractility under electrical, mechanical and pharmacological stimulation (Observations on helical strips from rabbit coronary and brain arteries). Pflugers Arch. 365, Supp. R 7 (1976) NAKAYAMA,K., KASUYA,Y. AND KATO, H.: Different calcium dependency of contractile responses of cerebral artery to quick stretch and electric stimuli. Acta. Neurol. Scand. 60, Supp. 72, 508-509 (1979) ARUNLAKSHANA, O. AND SCHILD,H.O.: Some quantitative uses of drug antagonists. Brit. J. Pharmacol. 14, 48-58 (1959) FINNEY, D.J.: Probit analysis, p. 236-254, Cambridge University Press, Cambridge (1952) HERLIHY,J.T. AND MURPHY, R.A.: Length-tension relationship of smooth muscle of the hog carotid artery. Circulation Res. 33, 275-283 (1973) BOHR, D.F.: Vascular smooth muscle updated. Circulation Res. 32, 665-672 (1973) GODFRAIND,T. ANDKABA, A.: Blockade or reversal of the contraction induced by calcium and adrenaline in depolarized arterial smooth muscle. Brit. J. Pharmacol. 36, 549-560 (1969) VANBREEMEN,C.: Calcium requirement for activation of intact smooth muscle. J. Physiol. 272, 317-323 (1977) FLECKENSTEIN, A., GRUN, G., TRITTHART,H. AND BYON, Y.K.: Uterus-Relaxation durch hochaktive Cal+-antagonist ische Henmstoffe der elektromechanischen Koppelung wie Isoptin (Verapamil, Iproveratril), Substanz D 600 and Segontin (Prenylamin). Versuch am isolierten Uterus virgineller Ratten. Klin. Wochenschr. 49, 32-41 (1971) FLECKENSTEIN, A.: Specific pharmacology of calcium in myocardium, cardiac pacemakers, and vascular smooth muscle. Ann. Rev. Pharmacol. Toxicol. 17, 149-166 (1977) GOLENHOFEN,K. AND HERMSTEIN,N.: Differentiation of calcium activation mechanisms in vascular smooth muscle by selective suppression with verapamil and D 600. Blood Vessels 12, 21-37 (1975) TAIRA, N., HIMORI,N. AND [MAI, Y.: Inhibition of excitation-contraction coupling in the ventricular myocardium of the dog by SKF-24260. Clin. exp. pharmacol. physiol. 3, 567-574 (1976) HIMORI, N., ONO, H. AND TAIRA, N.: Simultaneous assessment of effects of coronary vasodilators on the coronary blood flow and the myocardial contractility by using the blood-perfused canine papillary muscle. Japan. J. Pharmacol. 26, 427-435 (1976) GODFRAIND,T.: Cellular pharmacology of calcium-antagonists and of receptor response decoupling agents. 3rd Int. Symp. on Vascular Neuroeffector Mechanisms, Abstracts, p. 20-21 (1978) DE CLERK, F., DE CREE, J., BRUGMANS, J. AND WELLENS,D.: Reduction by flunarizine of the increase of blood viscosity after ischemic forearm occlusion. Arch. int. Pharmacodyn. 230, 321-323 (1977) GODFRAIND,T.: Alternative mechanisms for the potentiation of the relaxation evoked by isoprenaline in aortae from young and aged rats. Europ. J. Pharmacol. 53, 273-279 (1979)