EFFECTS OF BUPHENIN ON THE RAT PORTAL VEIN

M. CH. MICHAILOV. W. FELIX AND U. WELSCHER

Technical assistance: M. IDEL BERGER AND M. SCHUBERT

Institut f~~ Bioloqie der Gesellschaft fu~ Strahlen-und Umweltforschung. Munchen­

Neuherberg. Institut fur Pharmakologie der Universita't' Munchen,Federal Republic of Germ~nv

Summary: The vasodilator and tocolytic substance buphenin (10 (1.mol/l) stimulated the spontaneousphasic activity of some (8 out of 18) isolated rat portal vein preparations; 0.1-1 mmol/I buphenindimi nished 0 r abo Iished the activity in all preparations. The isotonic and isom etric; tonic contractions ofpo rtal vein in response to adrena line. noradrena line and phenyleph rine (0.1-1 (1.molj/) disappearedalmost completely after addition of buphenin in equimolar concentrations. whereas acetylcholine con­tractions persisted. The beta-adrenergic blocking agents propranolol and dichloisoprenaline (10(1.fflolll) only slightly. antagonized the inhibitory effect of buphenin on the contractile ~esponses tocatecholamines. It IS concluded that buphenln exerts dual action upon rat portal vein: the drugpartially stimulates the beta-receptors and pa rtial!y blocks the alpha-adrenergic receptors.

Key words: buphenin

mechanical activity

adrenaline acetylcholine portal vein

alpha- and beta-adrenergic receptors

INTRODUCTION

Buphenin (nylidrin). an arylalkylated catecholamine derivative. dilates peripheralarteric:l vessels (' nd lowers the systolic and diastolic arterial blood pressure via beta·adrenergic stimlJlation (1.2.3.1'..19). The drug also relaxes tracheal (1.2) and uterine·smooth muscle and it is used as a tocol'ltic substance (11.17). In addition bupheninproduces alpha-adrener~ic b:ockade of the seminal vesicle (12) and the vas deferens(1.2) and in guinea-pig and human detrusor muscle stimulates the spontaneousmechanical activity and contractions in response to electric31 stimUlation (13.14.15).In the present paper is described the effect of buphenin on the machanical activity ofisolated rat portal vein smooth muscle and it::. possible relation t0 alpha- and bela­odrenergic recept~rs is discussed.

The rat portal vein is constructed of longitudinal and circular smooth muscle layers(4) and shows spontaneous rhythmic activity due to myogenic automaticity (9). The in­herent contractions are modified after stimulation of sympathetic (adrenergic) vasomotorlibers (10), The rat portal vein reacts to acetylcholine, adrenaline and noradrenaline

Volume 23 Effects of Buphenin on Rat Portal Vein 255umber 4

with augmented phasic actl'lIty and tonic contractions (3,5.6). The mechanical responseof the portal smooth muscle to noradrenaline and to sympathetic nerve stimulation can beinhibited by treatment with phenoxybenzamine (alpha-adrenergic blockade) (3,10). Thebeta-receptor stimulating agent isoprenaline in low concentrations (10..... -10-7 glml"weight/volume") reduces the individual (phasic) mechanical responses, while higherconcentrations (10-5 "weight/volume") act like noradrenaline causing a temporary initialinhibition by followed contraction summation and fusion of the tension (3).

MATERIALS AND METHODS

Helical muscle strips (length: 10-20 mm) were cut from the portal vein of malealbino rats (Wistar. pathogen-free, 300-350 g). The preparations were kept in an organ

bath containing a modified Krebs-Henseleit solution (compositio:l in mmo/II: NaCI 122;KCI 4.75; CaCI2 2.49; MgSO.. 1.19; NaHC03 15.48; KHzPO.. 1.49; glucose 11.5) at37°C. aerated with a mixture of 95% O2 and 5% COz. The mechanical activity of the portal

vein was recorded under isotonic (preloaded with 100-200 mg. rotary motion transducer:Harvard Model 386. magnification 1:32) or isometric (force displacement transducer:Grass Model FTO 3C) conditions on a Schwarzer polygraph. The preparation was cauti­ously st,etchej until regular rhythl1ic activity appeared. giving a passive tension of 200­

300 mg.

Drugs: acetylcholine chlorid~. adrenaline hydrogene tartrate. azapetine (liidar·. Hoffman­La Roche). buphenin (Dilatol*. Tropon). dichlorisoprenaline. propranolol hydrochloride.noradrenaline. phenylephrine.

RESULTS

After an adaptation time of about one hr the muscle tone of the portal vein pre­paration became stable for many hours. The siz-e of the automous rhythmic contractionsvaried and the contractions often fused. The frequency of the vi!>ible spontaneous con­tractions was 2.86%0.33 (mean±S.E.M.) per min. Under isotonic conditions theiramplitudes had a maximal value of 1.39±0.25% of the total length of the preparation (n=11), and under isometric conditions (n=13) a value of 85.76:%19.07 mg tension per emlength of the preparations. After buphenin in concentrations -of-up to 1 ,.,.molll the portalmuscle showed no visible changes in muscle tone or spontaneous activity (Figs. 1a and b).In some of the preparations 10 ,.,.mo/II also had no visible effect. while the contraction­amplitudes were augmented in 8 of 18 of the preparations. (Fig. 1b). Treatment with0.1-1 pomolll buphenin generally diminished or completely abolished the spontaneous---,--

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256 Michailov et af. October- December 1979Ind. J. Phvsiol. Pharmac.

activity (Fig. 1a). This inhibition was sometimes preceded by an increase in tone and con­tractile activity (Fig_ 1c) (see Table I).

Vena portae

tBuphenin

Propanolol

BP

b)

B 5·1O- 5 M B 510- 4 M

~ ~ t[ 1 em

P 10-5 M

~ t

0) .l~11UJll'l.L~~lillltlt~,~llJL'J.lLLl.--J1J~_~~~...... JLLl~B B

Fig.1: (a) Inhibitory effect of buphenin (B) on the spontaneous phasic activity of the portal vein.

(b) Augmentor effect of buphenin on the phasic activity_

fc) Changes in tone and phasic activity after bubhenin; action of propranolol.

TABLE I: Action of buphenin on the mechanical activity of rat portal vein(number of preparations in brackets).

Reaction after buphenin

10-6 M

10-5 M

--------10-4 M

Muscle tone

unchanged (7)

unchanged (18)

(a) unchanged (9)

(b) elevated (6)

Phasic activity

unchanged (7)

(a) unchanged (10)

(b) augmented contraction­amp litudes (8)

(a) increased frequency anddiminished contraction­amp I;tudes (5)

(b) abolition (10)

Volume 23Number 4

Effects of Buphenin on Rat Portal Vein 257

In most cases the muscle tone remained unchanged after buphenin (0.1mmolll) , some preparations showed an elevated tone andlor a persistent phasicactivity which was characterized by higher frequency and smaller contraction­amplitudes (Table I). The alpha-adrenolytic substance azapetine (1 0 ~o!ll) andalso the beta-adrenolytic substance propranolol (10 porno!I!) inhibited this increase inportal mechanical activity (Fig. 1c). In concentrations ~igher than 10 porno!l! these twoadrenergic blocking substances had an effect similar to that of 0.1 porno!l! buphenin,i.e. they abolished the mechanical activity of the portal vein.

Adrenaline and acetylcholine in concentrations of 0 1-1 porno!11 caused reproducibletonic contractions and an increase in phasic activity of the portal muscle. Figure 2 shows

Vena portae

[ 150 mg

a)

B 10·7 M

~

~,~~ --......'""',.....-----~

Ad r ACH

t

Adr ACH

tOnI.......

ACEltylcholine ACH

Adrenaline Adr

Buphenin 8

5' 30'

r--l 3 min Adr AC.H A dr Adr ACH

Fig ,2: Action cf buphenin on the aarenaline 3nd acetylchc, line responses of rat portal ve:in unde~

isometric and isotonic conditions (magnification 1 :30) : in contrast to the adrenaline cont-actionsthe acetylcholir:e contractions are not visible influenced by buphenin.

258 Michailov f!t! al. October-December 1979Ind. J. Physio!. Pharmac.

the action of buphenin on the isometric and isotonic test-contractions of the two hormones.Buphenin inhibited dose-dependently the adrenaiine. noradrena line and phenylephrine con­tractions and in equimolar concentrations almost completely abolished these reactions(30 preparations). In contrast to these findings the acetylcholine test-reaction to 0.1-1,wIol/lwas not visibly changed by huphenin in equimolar concentrations (20 preparations).After 0,1 rnmolll buphenin the acetylcholine reaction to 1 pornoll/ disappeared (5 pre­parations). Table II gives a quantitative analysis of the action of buphenin on the adrena­

line and acetylcholine test-contractions.

Ven~ portae

lem

>---o3m'n

Adrenal'ne Ad.

B u P hen In"? B

Propranolol P

40'

Ad. 10. 6 ,.,

B 10. 6 M + P 10'6 M

~ ~

~fujl~~~lliI1~~~Wj_

Ad.

20'

Ad.

20'

Adr

Adr Ad. Ad r Adr Adr

Fig.3: Antagonbing action of the p-adrenergic blocking agent propranololon the buphenin inhibitory effect upon the adrenaline test·reactio:1.

The inhibitory effect of buphenin on the adrenaline and phenylephrine test-reaction(0,1-1 po77oll/) was only partially antagonized by propranolol or dichlorisoprenaline (1-10porno/II), (9 preparations, see Fig. 3). In preparations that had not been pretreated withbuphenin, propranolol (0.1-10 pomdll) had no visible influence on the adrenaline- andphenylephrine-test-contracti on s.

Volume 23 Effects of Buphe'1in on Rat Portal Vein 25Number 4

TABLE II: Inhibitory effect of buphenin on the contractile responseof isolated rat portal vein to adrenaline and acetylcholine.

Inhibitory action of buphenln on the con-cnslon tmqlpr("para- or <;ho:'"t('nlnq III tractIon In , (reaction a f t..er contractingns(__1 agent = 100 )

~,10- 6 I p 10-~i M M Pr84.;5~2-7.64 - r----i-)!l . 3 24 .62~6.64 I <0.002 45. 20~1) .96 <0.005

I < a .005 <0.001 I <0.005-- I - . - f--86 . 40!.4.91 [o.~ -92.'S6!.S-:SO-

.-.- _.7. I .2 ]'..3. )8'85.69 <0.001

I-

--- - -_. -_.0_-s10n

j85. 76~19 06

caused by spontaneous activityrtcnlng 1.39:0.15

- .. - '-- ~-- .-8.2. I t 3.43:1.23 16 11.:9 28 > 0.05 25.00.:14 4) >0.01

.. -- _.--~.- _.- ~_.....-i > (l. 5 < 0.001 <0.001.-

r..

0'1 6 4.41"+1 22 9 ) 42~3 28 < 0.001 97.36!.1 87 <0.001

I

I~~an l~'~g'h I~~anIf 10

8 12.

-j'1ean ten

I'

ACC'lylchol ~n'"

11"\ -6 '1

Mean sho

Ac~ty lChOll._oe---+_61_2'u I (l-6 M

----g r

~ lM~c~~llnE" 8 I I)

I I n-6

M i

~.......~ -ArI-rc-na-l-ln-c-

10'6 '1S"-1---+------>

O

n"'1 .[ (:rJntr.lctlnqoJ>. ~ ,HI,..r;t

;., J;

~ OJ.a:

DISCUSSION

Perfusion of isolated dog liver with buphenin decreases both the portal venous flowand the ratio of portal vein outflow to total hepatic outflow. while the hepatic arterial flow isincreased. Propranolol abolishes the effect of buphenin on the hepatic arteria I flow (beta­adrenergic blockade) and further diminishes the portal venous flow (30). These findings arein accordance with our observation that buphenin augments the spontaneous mechanicalactivity in the rat portal vein and that propranolol in low concentration does not antagonizethis effect. It seems that buphenin. azapetine and propranolol in high concentrations (100pmol/I) act unspeci1ically on the port:)1 mechanical activity because all these drugs inhibitthe phasic contractions. The nature of the stimulatory and inhibitory effects of bupheninon the portal spontaneous (phasic) activity is not clear.

Buphenin strongly inhibits the catecholamines-test-contractions whereas the con­tractions in response to acetylcholine and to potassium and 5-hydroxytryptamine are onlydiminished (16). These findings can be explained by the alpha-adrenergic blocking pro­perties of buphenin (1.2.12). On the other hand it is evident that buphenin also possessessome beta-adrenergic stimulatory action on the portal vein since propranolol and dicholriso­prenaline partially antagonized the inhibitory action of buphenin on the contractile responseto adrenaline. This beta-adrenergic effect of buphenin in the rat portal vein is slight com­pared to that of isoprenaline: this drug produces a relaxation in canine veins from variousorgans preconstricted with noradrenaline. 5-hydroxytryptamine and histamine (18) and

260 Micha:lov et al. October-December 1979Ind. J. Physio!. Pharmac.

also in untreated rat portal vein (3) and in rabbit aortic strip (7) via stimulation of beta­

adrenergic receptors of the venous smooth muscle.

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2. Ariens. E.J. The Structure-Activity Rela tionships of Beta-Adrenergic Drugs and Beta-Adren~rgic Bloci<­ing Drugs. New York Acad. Sci.. 139 : 606-631. 1967.

3. Ax~lsson. J .• B. Johanssen. O. Janssen and B. Wahlstrom. The effect of adrenergic drugs on electricaland mechanical activity of the portal vein. Symp. Electr. Ac tiv. Innerv. Blood Vessels, Cambridge1966: Bibl. Anal.. 8 : 5-10 Karger. Basel/New York. 1966.

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15. Michailov. M. CH., E. Elsasser, U. E. Welscher and F. Weiss. 0 ie Beeinflussung der mensch lichen Harnblase(Detrusormuskel-praparat) durch tokolytische Substanzen. In 'Gynakologie und Geburtshilfe" Ed. H. Eger.mann, Wien, 741-7461977.

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17. Mosler. K. H. and H. Schwalm. Vergleichende Untersuchungen tokolyisch und relaxierend wirkend er Substan­zen am i so lie rten Uterus. Zeneralbibl. Gynak .• 18 : 603, 1965.

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