Effects of the Adrenergic Drugs on the Chrono- And Inotropic Responses to the Cholinergic Stimulation of the Isolated Guinea-Pig’s Atria

Abstract

Hukovic (1) was the first to suggest the existence of the cholinergic fibers in the sympathetic nerve of the rabbit's atria. He showed that stimulation of the sympathetic nerve in the isolated reserpinized heart produced the negative chrono and inotropic effects which were potentiated by eserine and abolished by atropine. A series of ex periments in this laboratory (2-5) have excluded an essential role of the heart cate cholamine on initiation and maintenance of the spontaneous contraction and action potential of the rabbit's atria. Recently, Misu (6, 7) and Misu and Takaori (8) in this laboratory have demonstrated that the atrial action potentials abolished by the con centration of 10-5 of dibenarnine, chlorpromazine and yohimbine, are restarted by ad renaline as well as by acetylcholine, and that noradrenaline mainly shortens the repo larization phase of the potential, while acetylcholine serves to restore the depolariza tion phase. This suggests a modulating role of the endogenous noradrenaline in the rhythmic contraction or action potential of the heart, and led us to study the effects of catecholamine-relating drugs on the atrial responses to cholinergic stimulation. METHODSThe isolated atria of guinea-pig, weighing 250 to 350 g and of either sex, were mainly used. In some of the experiments the isolated atria of rabbit, weighing 1.8 to 2.2 kg, were also used.Preparation of the isolated atria attached with innervated vagus nerves : The animal was fixed on the animal-board in a supine position, and after longitudinal incision in the neck the right and left vagus nerves and carotid arteries were separated from the sur rounding connective tissues toward the entrance of the nerves and arteries into the thorax. Immediately after a full exsanguination by cutting both carotid arteries the thorax was opened and the atria with the vagus nerves were prepared following sur gical procedures described previously (9). Spontaneous contraction of the atria in the

Effects of 10-Methoxydeserpidine on the Ecg Changes Induced by Vasopressin in Unanesthetized Rabbit

“…These effects of 10-methoxydeserpidine on 'the ECG changes following vasopressin were more marked at 5 or 6-hour interval than at I or 2-hour interval. Although whether catecholamine depletion in the coronary vessel is related to the preventive effect of 10-methoxydeserpidine against vasopressin was not determined in the present experiment, the time course of the preventive action of l0-methoxydeserpidine coincided well with the course of the skin temperature rise of the rabbit ear shown by Toda et al (5).…”

The Effect of Physostigmine on Heart Phosphorylase Activity in the Spinal Rat

“…Many investigators (11)(12)(13)(14) reported that pressor response to physostigmine in rats resulted from an activation of the central sympathetic mechanism. Toda et al (15) in this laboratory have shown that vagal stimulation of the isolated rabbit atria produces the positive ino and chrono-tropic effects and the effects are prevented by reserpinization. Along with this the activating effect of vagal stimulation on heart phosphorylase a in the spinal rat suggested that there might be adrenergic fibers or mechanism in the cholinergic innervation within the heart.…”

Modifications of the Vagal Effect on the Heart and the Cardiac Metabolism by Reserpine in Vitro

“…Preparation of isolated guinea-pig atria with the vagus nerve : The procedures to make the vagus-atrial preparation, to stimulate the vagus nerve, to record the chronotropic and inotropic responses and to compose the nutrient medium in which the preparation was suspended were described in the previous report (10).…”