Chronotropic and Inotropic Effects of Bradykinin on Isolated, Blood-Perfused Canine Atrium

Chronotropic and Inotropic Effects of Bradykinin on Isolated, Blood-perfused Canine Atrium Miyoharu KOBAYASHI, M.D., Yasuyuki FURUKAWA, M.D., and Shigetoshi CHIBA, M.D. SUMMARY Effects of bradykinin on SA node pacemaker activity and atrial contractility were studied, using isolated, blood-perfused dog atrium preparations. Bradykinin (0.1-100ƒÊg) caused a slightly but consistently positive chronotropic action, although it did not produce a consistent inotropic action. When successive doses of bradykinin were given in a short period, these preparations displayed tachyphylaxis. Bradykinin- induced action was not suppressed by a potent ƒÀ-adrenoceptor blocking agent, carteolol. In addition, kallikrein (0.1-3 units), was administered into the sinus node artery to investigate the effect of endogenous kinins. Kallikrein had no effect on SA node pacemaker activity nor atrial contractility at any examined doses. On the other hand, a kallikrein inhibitor, aprotinin, induced dose-relatedly a negative inotropic and chronotropic effect at a dose range from 100 to 3,000 units. These negative actions of aprotinin were not blocked by an adequate dose of atropine. From these results, it is concluded that bradykinin has a slight direct positive chronotropic effect, and that aprotinin has direct negative inotropic and chronotropic effects in the isolated, blood-perfused canine atrium in a wide dose range. Additional Indexing Words: Isolated canine atrium Bradykinin Tachyphylaxis Kallikrein Aprotinin T is widely accepted that bradykinin is one of the most potent vasodilator substances.1)-3) However, there is a controversy on the cardiac action of this substance. In regard to chronotropism, Nakano4),5) reported that bradykinin given intravenously increased heart rate mostly due to the reflex sympathetic stimulation through its hypotensive actions in anesthetized dogs . Staszewska-Barczak and Dusting6) also described that bradykinin-induced tachycardia was suppressed after the blockade of ƒÀ-adrenoceptors with pro- pranolol in the open-chest, anesthetized dog. On the other hand, Rosas et al7) demonstrated that bradykinin produced some increases of heart rate From the Department of Pharmacology, Faculty of Medicine , Shinshu University, Matsumoto 390, Japan. Received for publication May 21, 1979. Manuscript revised August 31, 1979. 121 Jap. Heart J. J 122 KOBAYASHI, FURUKAWA AND CHIBA anuary, 1980 even after autonomic blockade, and they concluded that bradykinin had a direct cardiac action. However, it was reported that bradykinin had no sig- nificant chronotropic effect studied by direct perfusion of the dog sinus node8) and even in isolated perfused guinea-pig hearts.9) With regard to inotropism, Rosas et al7) found that bradykinin had a positive inotropic effect in the anesthetized rat. Heeg and Meng9) reported that bradykinin had a positive inotropic effect in the isolated heart as well as in the isolated auricle, but that in the papillary muscle this peptide had no effect. Conversely, Hashimoto et al10) observed that bradykinin exerted a negative inotropic action on the intact dog heart. However, it is difficult to separate experimentally the reflex sympathetic activity which follows hypotension from a possible direct cardiac effect of bradykinin in the whole animal. The present experiments were therefore designed to observe the direct effect of bradykinin on heart function using the isolated blood-perfused canine atrial preparations.11),12) Furthermore, direct effects of kallikrein and a kallikrein inhibitor, aprotinin, were also studied, because the use of these drugs for the therapeutic purpose has increased in recent years. MATERIALS AND METHODS Twenty-one mongrel dogs weighing from 7 to 20Kg were anesthetized with sodium pentobarbital, 30mg/Kg i.v. After treatment with 200 units/Kg of sodium heparin i.v., the right atrium was quickly excised and immerged into a cold Tyrode solution at 4•‹ to 10•Ž. The sinus node artery was cannulated via the right coronary artery and perfused with arterial blood conducted from the carotid artery of the donor dog by the aid of a peristaltic pump (Harvard Apparatus, Model 505-1200). The perfusion pressure was maintained at 100mmHg. The atrium was suspended in the bath filled with blood at a constant temperature of 37•Ž. The upper part of the crista terminalis of the atrium was connected directly to a force displacement transducer (Grass FTO3B) by a silk thread. The donor dogs weighing 12 to 27Kg were also anesthetized with 30mg/Kg of sodium pentobarbital i.v. Sodium heparin, 500 units/Kg, was intravenously administered at the beginning of the perfusion and 200 units/Kg were added at 1-hour intervals. Bipolar platinum electrodes were placed in contact with atrial epicardium. The atrial rate was measured with a cardiotachograph triggered by the signal from the atrial depolarization on an electrogram. The isometric tension development was recorded on an ink-writing rectigraph (Sanei Sokki Instrument) through a carrier preamplifier (Nihon Kohden RP-3), RC circuit and a high gain amplifier (Nihon Kohden RPH-2). Details of the isolated, blood-perfused canine atrial preparations were described in previous papers.11),12) Drugs used in this study were as follows: bradykinin triacetate (Sigma), dl- norepinephrine hydrochloride (Sankyo), carteolol (dl-5(3-tert-butylamine-2-hy- droxy) propoxy-3, 4-dihydrocarbostyril hydrochloride, Ohtsuka), kallikrein (Bayer), aprotinin (Trasylol, Bayer), acetylcholine chloride (Daiichi Seiyaku), and atropine Vol.21 No.1 BRADYKININ ON SA NODE AND CONTRACTILITY 123 Fig. 1. Slight positive chronotropic and inotropic responses to increasing doses of bradykinin (BK) when injected into the sinus node artery of an isolated, blood-perfused atrium preparation of the dog. Fig. 2. Repetitive positive chronotropic and inotropic effects of 3ƒÊg of bradykinin (BK) when injected into the cannulated sinus node artery of an isolated, blood-perfused atrium preparation of the dog. sulfate (Tanabe). RESULTS 1. Effect of bradykinin on SA nodal pacemaker activity and atrial contractility: When bradykinin was injected into the cannulated sinus node artery of the isolated canine atrium, slight but consistent positive chronotropic effects were induced at a relatively higher dose. Fig. 1 shows an example of the effect of bradykinin on an isolated atrial preparation. Tachyphylaxis, however, developed when successive doses of bradykinin were administered in a short period (Fig. 2). Thus, bradykinin was injected at 30 to 60min intervals in the present experiments. With regard to inotropism, bradykinin did not produce a consistent inotropic action. Ten ƒÊg of this peptide induced only a positive inotropic action in 3 out of 6 preparations, no evidence of increasing tension development in 2 preparations and only a negative inotropic action in 124 KOBAYASHI, FURUKAWA AND CHIBA Jap. Heart J. J anuary, 1980 Fig. 3. Dose-response curves for bradykinin in the isolated, blood- perfused canine atrium preparations. Control sinus rate is 109•}7 beats/min (mean•}SEM) in 6 preparations. Vertical lines represent standard errors of mean. Fig. 4. Effect of 1ƒÊg of carteolol on action of 10ƒÊg of bradykinin (BK) and 0.1ƒÊg of norepinephrine (NE) in an isolated atrium. 1 case. Moreover, 30ƒÊg of bradykinin caused biphasic responses consisting of an initial decrease followed by an increase in 3 out of 6 preparations. Fig. 3 reveals dose-response curves to chronotropic and inotropic actions for bradykinin determined on 6 preparations. 2. Effects of carteolol on positive chronotropic and inotropic responses to bradykinin and norepinephrine: Positive chronotropic and inotropic effects of norepinephrine were suppressed by carteolol, a potent ƒÀ-adrenergic blocking agent,13),14) while those of bradykinin were not influenced by carteolol treatment. Fig. 4 shows that 1ƒÊg of carteolol completely blocks the effects of 0.1ƒÊg of norepinephrine but does not inhibit those of 10ƒÊg of bradykinin. Table I summarizes the data Vol.21 No.1 BRADYKININ ON SA NODE AND CONTRACTILITY 125 Table I. Effect of Carteolol on Bradykinin- and Norepinephrine-induced Positive Inotropic and Chronotropic Responses in 5 Preparations The results are expressed as means with standard errors of 5 experiments. Control sinus rate was 106•}7 beats/min in 5 preparations. Comparisons with control values (paired t-test): (1) p>0.05, (2) p<0.01, (3) p<0.05. Fig. 5. Negative inotropic and chronotropic responses to increasing doses of aprotinin when injected into the sinus node artery of an isolated, blood-perfused atrial preparation of the dog. obtained. 3. Absence of effect of kallikrein on SA nodal pacemaker activity and atrial contractility: Kallikrein (0.1 to 30 units) was administered into the sinus node artery in 5 preparations. However, kallikrein had no any effect on SA node pacemaker activity and atrial contractility in all examined trials. 4. Negative chronotropic and inotropic effects of aprotinin: When aprotinin was injected into the cannulated sinus node artery, negative chronotropic and inotropic effects were dose-relatedly induced in an extremely wide dose range. Fig. 5 shows a typical experiment in an isolated atrial preparation. Dose-response curves for aprotinin were determined in 5 preparations (Fig. 6). Negative chronotropic and inotropic effects of aprotinin were not influenced by treatment with atropine, although those of acetylcholine were markedly inhibited by atropine. Fig. 7 shows that 10ƒÊg of 126 KOBAYASHI, FURUKAWA

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