Age-Dependence of the Chronotropic Response to Noradrenaline, Acetylcholine and Transmural Stimulation in Isolated Rabbit Atria

Toda, Noboru; Fu, Wang L.H.; Osumi, Yoshitsugu

doi:10.1254/jjp.26.359

Cited by 9 publications

(9 citation statements)

References 16 publications

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“…Similar results were obtained in isolated papillary muscles (Boerth, 1975), although threshold concentrations of ouabain and those at which the maximum contraction was induced appreciably differed in atria (present study) and papillary muscles (Boerth, 1975 Schwieler, Douglas & Bouhuys, 1970;Friedman, 1972;Toda, Fu & Osumi, 1976). However, the involvement of noradrenaline released from adrenergic nerves in the positive inotropic effect of ouabain is excluded, since f-adrenoceptor antagonists and pretreatment of animals with reserpine do not reduce the effect of the glycoside (present study; Moran, 1972 …”

Section: Discussionsupporting

confidence: 86%

Cardiotoxic and Inotropic Effects of Ouabain on Atria Isolated From Rabbits of Different Ages

Toda

1981

British J Pharmacology

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I In sino-atrial node-right atrial preparations and left atrial preparations obtained from rabbits of different ages (2 to 360 days old), cardiotoxic and inotropic effects of ouabain were compared. Tachyarrhythmias were produced in immature and mature rabbit right atria exposed for 6 to 8 min to ouabain (5 x 10-6 M). The total number of contractions before the arrhythmias developed varied inversely with age (2 to 90 days old). Percentage reductions in the resting membrane potential, overshoot and maximum rate of rise induced by ouabain were greater in mature rabbit atria than in immature rabbit atria. 2 Reduction of Ca2 + in the bathing media suppressed the development of tachyarrhythmias. 3 In electrically-driven left atria isolated from immature and mature rabbits, similar frequencycontractile force curves were obtained, maximum contractions being attained at a frequency of 120/min. Ouabain at 2 x 10-' M shifted the curve upward and at 10-6 M greatly potentiated the contractile force developed at low frequencies (6 to 30/min). Increase in contractions induced by ouabain relative to pre-drug contractions at a frequency of 60/min were greater in immature rabbit atria (15 days old) but the positive inotropic effect of 2 x 10 M ouabain relative to the effect seen at 10-6 M was appreciably less. 4 It may be concluded that atria isolated from immature rabbits tolerate higher concentrations of ouabain than those isolated from mature rabbits.

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Section: Discussionsupporting

confidence: 86%

Cardiotoxic and Inotropic Effects of Ouabain on Atria Isolated From Rabbits of Different Ages

Toda

1981

British J Pharmacology

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“…This shows that the negative chronotropic effect of chronic hypoxia which we had shown after 12 weeks of treatment [3,4] is present after a mini mum of 3 weeks of chronic hypoxia. The chronotropic changes normally seen with ageing [10,11] were magnified by exposure to chronic hypoxia, and paralleled the physi cal changes produced by chronic hypoxia [3,[12][13][14],…”

Section: Discussionmentioning

confidence: 77%

Effects of Chronic Hypoxia during Maturation on the Negative Chronotropic Effect of [H<sup>+</sup>] on the Rabbit Sino-Atrial Node

Posner

Baker²,

Epstein³

et al. 1991

Neonatology

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Previous studies in our laboratory have shown an effect of 12 weeks of hypoxia on the electrophysiology of the heart. This study was designed to determine the effects of hypoxia for shorter periods (1,2,3 and 6 weeks) on the neonatal heart as well as the chronotropic effects of [H⁺] on sino-atrial automaticity. Rabbits (2 days of age) were raised for 1, 2, 3 or 6 weeks in either a normal or hypoxic environment. At the end of 1, 2, 3 or 6 weeks, they were killed and studied using an isolated sino-atrial tissue preparation and standard microelectrode techniques. Measurements of hematocrit, ventricular weight and ventricular total protein were made. Right ventricular hypertrophy appeared at 2 and 3 weeks in the hypoxic hearts. There was no difference in left ventricular weight or total protein between normal and hypoxic groups over the time studied. Both the basal and maximal (isoproterenol stimulated) spontaneous rates decreased with age. The baseline and maximal rates from hypoxic rabbits were significantly less than those from normal rabbits at 3 and 6 weeks (p < 0.05). The net negative chronotropic effect of elevated [H⁺] was more pronounced in the hypoxic than the normal preparations at 3 and 6 weeks. In summary, neonates raised in hypoxia for as short a period as 3 weeks show right ventricular hypertrophy and a decrease in sino-atrial automaticity. The net negative chronotropic effect of [H⁺] is enhanced with development and chronic hypoxia.

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“…In newborn kittens, responses to vagal stimulation were undetectable until they were 11 days of age (5,23). Vagotomy caused less increase in heart rate in newborn puppies than in adult dogs (14,40). Newborn rabbits, however, did exhibit a greater bradycardia than did adults to vagal stimulation (41).…”

Section: Discussionmentioning

confidence: 99%

Neural Control of Heart Rate: a Comparison between Puppies and Adult Animals

Mace

Levy

1983

Pediatr Res

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SummaryThe heart rate responses to stimulation of the right and left cardiac autonomic nerves were evaluated in 20 puppies and 17 adult dogs. In every puppy and adult dog, the changes in heart rate were much greater with right-than with left-sided stimulation of the vagal or sympathetic nerves. At maximal stimulation frequencies, the % changes in heart rate (mean k S.E.M.) were: right stellate, adults +50.0 ( 2 5.1) and puppies +23.6 (k2.8); left stellate, adults +20.0 (k2.4) and puppies +5.6 (k2.3); right vagus, adults -74.0 (25.2) and puppies -43.6 (f3.3); and left vagus, adults -44.1 (k2.0) and puppies -24.9 (k2.3). At any given stimulation frequency, the heart rate responses were significantly greater in adult dogs than in puppies, with either stellate or vagal stimulation. In 47% of the puppies and in 11% of the adult dogs, left stellate stimulation had no detectable effect on heart rate, although there was evidence of an increase in blood pressure in each of these animals. In these animals, fibers from the left stellate ganglion did not innervate the sinoatrial node.Cardiac function in newborns and young animals is different from adults (2,7,20,47,48). Biochemical and histologic studies suggest that the sympathetic innervation of the heart is anatomically incomplete in newborns (18,27,33,42), whereas the parasympathetic innervation appears to be anatomically complete (8,12,15,17,44). The functional status of these autonomic nervous pathways in young animals has not been fully established, however. In the present investigation, we have evaluated functionally " the chronotropic responses to autonomic stimulation in puppies. Also. we have com~ared the chronotro~ic resDonses to rieht-and " left-sided autonomic stimulation in puppies and adult dogs. MATERIALS AND METHODSTwenty puppies from six litters and 17 adult dogs were anesthetized with sodium pentobarbital (30 mg/kg, intravenously or intraperitoneally). A tracheal cannula was inserted in each animal, and intermittent positive pressure respiration was instituted. The chest was opened transversely at the fourth intercostal space. Both stellate ganglia in the chest and both cervical vagi were isolated. Crushing the vagi and the rami communicantes to the stellate ganglia by means of tight ligatures eliminated the tonic neural activity to the heart (1, 26).The atrial electrogram was recorded from a bipolar electrode catheter, which was introduced into the right atrial cavity. The atrial electrogram, arterial blood pressure (Statham PB23A transducer), and the heart rate were recorded on an eight-channel oscillograph (Brush, Mark 200). The heart rate was derived from the atrial electrogram with an analog computer (EAI-580).Bipolar iridium electrodes were connected to a Grass S4 stimulator (with an isolation unit), in order to stimulate both stellate ganglia and the cardiac segments of both vagi. To prevent drying and to decrease current spread, mineral oil was applied to the cardiac nerves in the region of the stimulating electrodes. Stimuli to the stellate gang...

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Age-Dependence of the Chronotropic Response to Noradrenaline, Acetylcholine and Transmural Stimulation in Isolated Rabbit Atria

Cited by 9 publications

References 16 publications

Cardiotoxic and Inotropic Effects of Ouabain on Atria Isolated From Rabbits of Different Ages

Cardiotoxic and Inotropic Effects of Ouabain on Atria Isolated From Rabbits of Different Ages

Effects of Chronic Hypoxia during Maturation on the Negative Chronotropic Effect of [H<sup>+</sup>] on the Rabbit Sino-Atrial Node

Neural Control of Heart Rate: a Comparison between Puppies and Adult Animals

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