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Positive chronotropic and inotropic responses to guanosine in the isolated dog atrium
European Journal of Pharmacology, 49 (1978) 319--321
319
© Elsevier/North-Holland Biomedical Press
Short communication POSITIVE C H R O N O T R O P I C AND INOTROPIC RESPONSES TO GUANOSINE IN THE ISOLATED DOG ATRIUM SHIGETOSHI CHIBA, MIYOHARU KOBAYASHI and YASUYUKI F U R U K A W A
Department of Pharmacology, Faculty of Medicine, Shinshu University, Matsumoto 390, Japan Received 20 February 1978, accepted 14 March 1978
S. CHIBA, M. KOBAYASHI and Y. FURUKAWA, Positive chronotropic and inotropic responses to guanosine in the isolated dog atrium, European J. Pharmacol. 49 (1978) 319--321. The effects of guanosine on chronotropism and inotropism in isolated dog atria were studied in spontaneously beating preparations which were suspended in a bath perfused with arterial blood from a carotid artery of a heparinized support dog. Guanosine administered into the cannulated sinus node artery in a dose range of 30 gg to 3 mg produced a dose-related positive inotropic and chronotropic effect. The positive responses to guanosine were not inhibited by treatment with propranolol or a non-depressant H-blocker, carteolol, in doses which blocked responses to norepinephrine. From these results, it is concluded that guanosine has a direct effect on atrial rate and contractility. Guanosine
Isolated canine atrium
Carteolol
1. Introduction Adenosine and guanosine are intrinsic biogenic substances which are c o m m o n l y found in mammals. Adenosine has a number of actions on cardiac tissue and the possibility of a role for adenosine as a mediator of metabolic vasodilation has been studied in the heart. Negative chronotropic and inotropic actions of adenosine have been shown while definite cardiac actions of guanosine have not been reported. In 1964, Rosenblum and Stein reported that guanosine caused a positive inotropic effect on isolated atria o f humans, guinea pigs, rabbits and rats. They concluded that the positive inotropic effect of guanosine resulted from the release o f endogenous norepinephrine,because the guanosine-induced positive inotropic effect was inhibited b y pretreatment with reserpine or b y cocaine treatment. In the present experiments, the effect of guanosine on atrial pacemaker activity and contractility was examined, using the isolated,
blood-perfused dog atrial preparation which was developed b y Chiba et al. (1975a, b).
2. Materials and methods
7 adult mongrel dogs weighing 12--16 kg were anesthetized with sodium pentobarbital (30 mg/kg, i.v.). The right atrium was quickly removed and immersed in Tyrode solution at 4--10°C. The isolated atrium was then perfused with arterial blood led from the carotid artery of the support dog. The atrium was suspended in a bath filled with blood at a constant temperature of 37°C. Atrial rate was measured with a tachometer which was triggered b y the atrial electrogram and isometric tension development was measured with a force displacement transducer (Grass FTO3B). The muscle was usually subjected to a 2 g tension. Perfusion pressure was kept constant at 100 mm Hg and the rate o f perfusion flow was also measured. The details of the preparation
320
S. CHIBA ET AL.
were described previously (Chiba et al., 1975a, b).
7O
60
~///~)
50
4030
3. Results Guanosine injected into the cannulated sinus node artery produced a positive inotropic and chronotropic response in isolated atria. The threshold dose for inducing positive effects was approximately 30 pg. Guanosine produced a dose-related increase in positive chronotropic and inotropic activity. The quantitative data obtained with various doses of guanosine is shown in fig. 1. The positive chronotropic 'and inotropic effects of guanosine (100--1000 #g) were not significantly suppressed by treating the tissue with doses of the ~-adrenoceptor antagonists, propranolol (10 pg) or carteolol (10 pg) which antagonized the action of norepinephrine (0.1 pg) in all three experiments. Fig. 2 shows tracings from such an experiment. As previously reported for the isolated dog atrial preparation, a dose range of 0.01--0.1 pg of norepinephrine was completely inhibited by 10 pg of propranolol (Hashimoto et al., 1972); carteolol was approximately 10 times more potent than was propranolol (Hashimoto et al., 1976). In fig. 2, a positive chronotropic effect of 1000 pg of guanosine seems to have
20 10
~ J
(,~." 6) .,.....~. ~b) ~
(5)
(6) ,
,
,
300
1000
3000
0 15 1 O|
30
100
,
Fig. 1. Positive chronotropic and inotropic responses to guanosine in the spontaneously beating atrium of dog heart. The control sinus rate was 101 ± 7.1 beats] min (mean ± S.E.M.) in 6 atrial preparations. Vertical lines represent the standard errors of the mean and the figures in parentheses refer to the number of observations. Upper ordinate: % increase in developed tension; lower ordinate: % increase in sinus rate. Abscissa: dose of guanosine (pg).
been suppressed by 10 pg of carteolol, but the maximal rate was almost the same. Moreover, in two other preparations, the effects of 1000 #g of guanosine were not significantly influenced.
Carteo[o[ 10 pg I rain
c O 4 c O'~
cISO I
NE 0.1
GU GU 30 100
GU 300
GU 1000
NE GU Oh 100
GO 300
GU 1000 (pg)
Fig. 2. Effects of 10 ~g of carteolol on the guanosine-induced positive chronotropic and inotropic responses. NE: norepinephrine, GU: guanosine.
GUANOSINE ON DOG HEART
321
4. Discussion
References
The present experiments demonstrate that intra-arterial administration of guanosine producesdose-dependent positive chronotropic and inotropic effects in the isolated bloodperfused atrium of the dog. In 1965, James reported that guanosine in a 1 mg dose produced sinus acceleration when it was injected into the sinus node artery of the dog in situ. In this study also, at doses above 100 pg, guanosine consistently induced positive chronotropic and inotropic effects in all 7 preparations. In 1964, Rosenblum and Stein reported that the positive inotropic property of guanosine appeared to be mediated through the release of heart catecholamines. However, in this study, the potent ~-adrenoceptor blocking agents propranolol or carteolol failed to inhibit the guanosine-induced positive chronotropic and inotropic effect. It is therefore concluded that guanosine has a direct positive effect on sinoatrial pacemaker activity and atrial contractility in dog atria.
Chiba, S., T. Kimura and K. Hashimoto, 1975a, Muscarinic suppression of the nicotinic action of acetylcholine on the isolated, blood-perfused atrium of the dog, Naunyn-Schmiedeb. Arch. Pharmacol. 289, 315. Chiba, S., Y. Yabuuchi and K. Hashimoto, 1975b, Comparison of the effects of norepinephrine and acetylcholine between intraarterial and extravascular administration of the isolated, bloodperfused canine atrium, Jap. J. Pharmacol. 20, 32. Hashimoto, K., T. Kimura and Y. Yabuuchi, 1976, Comparison of newly synthesized ~-adrenergic blockers, OPC 1085 and SQ 11725, with pindolol and propranolol in the blood-perfused canine SA node and papillary muscle preparations, Jap. J. Pharmacol. 26, 504. Hashimoto, K., K. Kubota, S. Chiba and N. Taira, 1972, Comparison of ~-adrenergic blocking activity of eight blockers in the excised and bloodperfused canine sino-atrial node preparation, Experientia 28,822. James, T.N., 1965, The chronotropic action of ATP and related compounds studied by direct perfusion of the sinus node, J. Pharmacol. Exptl. Therap. 149, 233. Rosenblum, I. and A.A. Stein, 1964, Mechanism of the positive inotropic action of purine nucleosides in isolated atria, J. Pharmacol. Exptl. Therap. 145, 78.
319
© Elsevier/North-Holland Biomedical Press
Short communication POSITIVE C H R O N O T R O P I C AND INOTROPIC RESPONSES TO GUANOSINE IN THE ISOLATED DOG ATRIUM SHIGETOSHI CHIBA, MIYOHARU KOBAYASHI and YASUYUKI F U R U K A W A
Department of Pharmacology, Faculty of Medicine, Shinshu University, Matsumoto 390, Japan Received 20 February 1978, accepted 14 March 1978
S. CHIBA, M. KOBAYASHI and Y. FURUKAWA, Positive chronotropic and inotropic responses to guanosine in the isolated dog atrium, European J. Pharmacol. 49 (1978) 319--321. The effects of guanosine on chronotropism and inotropism in isolated dog atria were studied in spontaneously beating preparations which were suspended in a bath perfused with arterial blood from a carotid artery of a heparinized support dog. Guanosine administered into the cannulated sinus node artery in a dose range of 30 gg to 3 mg produced a dose-related positive inotropic and chronotropic effect. The positive responses to guanosine were not inhibited by treatment with propranolol or a non-depressant H-blocker, carteolol, in doses which blocked responses to norepinephrine. From these results, it is concluded that guanosine has a direct effect on atrial rate and contractility. Guanosine
Isolated canine atrium
Carteolol
1. Introduction Adenosine and guanosine are intrinsic biogenic substances which are c o m m o n l y found in mammals. Adenosine has a number of actions on cardiac tissue and the possibility of a role for adenosine as a mediator of metabolic vasodilation has been studied in the heart. Negative chronotropic and inotropic actions of adenosine have been shown while definite cardiac actions of guanosine have not been reported. In 1964, Rosenblum and Stein reported that guanosine caused a positive inotropic effect on isolated atria o f humans, guinea pigs, rabbits and rats. They concluded that the positive inotropic effect of guanosine resulted from the release o f endogenous norepinephrine,because the guanosine-induced positive inotropic effect was inhibited b y pretreatment with reserpine or b y cocaine treatment. In the present experiments, the effect of guanosine on atrial pacemaker activity and contractility was examined, using the isolated,
blood-perfused dog atrial preparation which was developed b y Chiba et al. (1975a, b).
2. Materials and methods
7 adult mongrel dogs weighing 12--16 kg were anesthetized with sodium pentobarbital (30 mg/kg, i.v.). The right atrium was quickly removed and immersed in Tyrode solution at 4--10°C. The isolated atrium was then perfused with arterial blood led from the carotid artery of the support dog. The atrium was suspended in a bath filled with blood at a constant temperature of 37°C. Atrial rate was measured with a tachometer which was triggered b y the atrial electrogram and isometric tension development was measured with a force displacement transducer (Grass FTO3B). The muscle was usually subjected to a 2 g tension. Perfusion pressure was kept constant at 100 mm Hg and the rate o f perfusion flow was also measured. The details of the preparation
320
S. CHIBA ET AL.
were described previously (Chiba et al., 1975a, b).
7O
60
~///~)
50
4030
3. Results Guanosine injected into the cannulated sinus node artery produced a positive inotropic and chronotropic response in isolated atria. The threshold dose for inducing positive effects was approximately 30 pg. Guanosine produced a dose-related increase in positive chronotropic and inotropic activity. The quantitative data obtained with various doses of guanosine is shown in fig. 1. The positive chronotropic 'and inotropic effects of guanosine (100--1000 #g) were not significantly suppressed by treating the tissue with doses of the ~-adrenoceptor antagonists, propranolol (10 pg) or carteolol (10 pg) which antagonized the action of norepinephrine (0.1 pg) in all three experiments. Fig. 2 shows tracings from such an experiment. As previously reported for the isolated dog atrial preparation, a dose range of 0.01--0.1 pg of norepinephrine was completely inhibited by 10 pg of propranolol (Hashimoto et al., 1972); carteolol was approximately 10 times more potent than was propranolol (Hashimoto et al., 1976). In fig. 2, a positive chronotropic effect of 1000 pg of guanosine seems to have
20 10
~ J
(,~." 6) .,.....~. ~b) ~
(5)
(6) ,
,
,
300
1000
3000
0 15 1 O|
30
100
,
Fig. 1. Positive chronotropic and inotropic responses to guanosine in the spontaneously beating atrium of dog heart. The control sinus rate was 101 ± 7.1 beats] min (mean ± S.E.M.) in 6 atrial preparations. Vertical lines represent the standard errors of the mean and the figures in parentheses refer to the number of observations. Upper ordinate: % increase in developed tension; lower ordinate: % increase in sinus rate. Abscissa: dose of guanosine (pg).
been suppressed by 10 pg of carteolol, but the maximal rate was almost the same. Moreover, in two other preparations, the effects of 1000 #g of guanosine were not significantly influenced.
Carteo[o[ 10 pg I rain
c O 4 c O'~
cISO I
NE 0.1
GU GU 30 100
GU 300
GU 1000
NE GU Oh 100
GO 300
GU 1000 (pg)
Fig. 2. Effects of 10 ~g of carteolol on the guanosine-induced positive chronotropic and inotropic responses. NE: norepinephrine, GU: guanosine.
GUANOSINE ON DOG HEART
321
4. Discussion
References
The present experiments demonstrate that intra-arterial administration of guanosine producesdose-dependent positive chronotropic and inotropic effects in the isolated bloodperfused atrium of the dog. In 1965, James reported that guanosine in a 1 mg dose produced sinus acceleration when it was injected into the sinus node artery of the dog in situ. In this study also, at doses above 100 pg, guanosine consistently induced positive chronotropic and inotropic effects in all 7 preparations. In 1964, Rosenblum and Stein reported that the positive inotropic property of guanosine appeared to be mediated through the release of heart catecholamines. However, in this study, the potent ~-adrenoceptor blocking agents propranolol or carteolol failed to inhibit the guanosine-induced positive chronotropic and inotropic effect. It is therefore concluded that guanosine has a direct positive effect on sinoatrial pacemaker activity and atrial contractility in dog atria.
Chiba, S., T. Kimura and K. Hashimoto, 1975a, Muscarinic suppression of the nicotinic action of acetylcholine on the isolated, blood-perfused atrium of the dog, Naunyn-Schmiedeb. Arch. Pharmacol. 289, 315. Chiba, S., Y. Yabuuchi and K. Hashimoto, 1975b, Comparison of the effects of norepinephrine and acetylcholine between intraarterial and extravascular administration of the isolated, bloodperfused canine atrium, Jap. J. Pharmacol. 20, 32. Hashimoto, K., T. Kimura and Y. Yabuuchi, 1976, Comparison of newly synthesized ~-adrenergic blockers, OPC 1085 and SQ 11725, with pindolol and propranolol in the blood-perfused canine SA node and papillary muscle preparations, Jap. J. Pharmacol. 26, 504. Hashimoto, K., K. Kubota, S. Chiba and N. Taira, 1972, Comparison of ~-adrenergic blocking activity of eight blockers in the excised and bloodperfused canine sino-atrial node preparation, Experientia 28,822. James, T.N., 1965, The chronotropic action of ATP and related compounds studied by direct perfusion of the sinus node, J. Pharmacol. Exptl. Therap. 149, 233. Rosenblum, I. and A.A. Stein, 1964, Mechanism of the positive inotropic action of purine nucleosides in isolated atria, J. Pharmacol. Exptl. Therap. 145, 78.