Abstract
It was reported that the occurrence of bradycardia by cardiac glycosides was connected with not only vigi (1, 2) but also sinus nerves (2-4). Recently, it was demonstrated that strospeside inhibited efferent discharges in the pre and postganglionic stellate fibers (5), and that dichloroisoproterenol prevented the production of bradycardia by strospeside in vagotomized cats (6). These evidences show that sympathetic nerves as well as sinus nerves play an important role as an extravagal factor of bradycardia produced by strospeside.
Abiko (2) set forth the opinion that there are at least two possible pathways of reflex in producing bradycardia by cardiac glycosides: One is the vagal nerve which exerts slowing on the heart rate by vago-vagal reflex and the other is the carotid sinus-sympathetic nervous chain which exerts a slowing effect on the heart rate by way of the sinus nerve, cervical cord and the stellate ganglia.
However, a question has arisen as to whether the inhibition of efferent sympathetic activity is induced solely by sinus nerves, independent of afferent fibers of vagi or not. The present study deals with this question.
