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Haemodynamic effects of the quaternary ammonium compound QX 572 in anaesthetized cats. II. Studies on the mechanism for the cardiac chronotropic effects.

The antiarrhythmic compound, QX 572, has been shown to increase heart rate both in patients and experimental animals. In anaesthetized cats the positive cardiac chronotropic effects were mainly due to increased sympathetic activity. The present experiments were designed to localize the active sites within the sympathetic nerve system. It was found that QX 572 caused an increased heart rate in response to electrical stimulation of the cardiac sympathetic nerves, but this was not due to effects on the CNS, the sympathetic ganglia or the cardiac adrenergic beta-receptors. It is concluded that QX 572 by some action increased the amount of noradrenaline released from the cardiac sympathetic nerve endings. The mechanism for this effect has not been clarified.