EFFECTS OF DICHLOROISOPROTERENOL AND PHENOXY BENZAMINE ON THE TRANSMEMBRANE POTENTIALS OF THE ISOLATED RABBIT'S HEART
1965 年 15 巻 2 号 p. 176-186
詳細
1965 年 15 巻 2 号 p. 176-186
The inhibitory effects of α-receptor blocking agents such as dibenamine, yohimbine and chlorpromazine on the transmembrane potentials in the atria isolated from intact and reserpinized rabbits were reported previously (1-3). Although acetylcholine (ACh) as well as adrenaline and noradrenaline could restart the atrial action potential which had been ceased by the application of the adrenolytics, the restarting effect of ACh showed considerable differences from that of catecholamines. It was described by several investigators that positive inotropic and chronotropic responses of catecholamines in the mammalian heart were not prevented by α-receptor blocking agents (4) but were antagonized by dichloroisoproterenol (DCI), a β-receptor blocking agent (5, 6). In the isolated heart preparations, the stimulating effect of ACh was blocked by the pretreatment with DCI or by the full reserpinization of the animals (7-10). These results proposed the assumption that the stimulating effect of ACh derived from endogenously released catecholamine. However, as already confirmed in the previous report (2), the evidence that the addition of ACh could restart the action potential which had been ceased by the pretreatment of α-receptor blocking agents even in the reserpinized rabbit was against the afcre-mentioned assumption.
In order to elucidate whether the stimulating effect of ACh derives from endogenously released catecholamine or not, the effects of ACh and catecholamine on the transmembrane potentials of the heart should be observed in relation to β-receptor blocking effects of DCI.
The present experiments have been designed to compare the effects of DCI and phenoxybenzamine, an α-receptor blocking agent, on the atrial and ventricular transmembrane potentials in the isolated rabbit's heart, and to elucidate the correlation between the actions of DCI and ACh or catecholamines. Further, the effects of DCI and phenoxybenzamine on the conduction time and the effective refractory period of the ventricle have been comparatively studied.
