STUDIES ON VERATRUM ALKALOIDS. XXII. PERIODIC ACTIVITY OF THE SINO-AURICULAR NODE OF THE DENERVATED CAT HEART CAUSED BY VERATRAMINE

¹ Department of Pharmacology, Harvard Medical School, Boston

Veratramine, injected in spinal cats in doses of 1 mgm./kgm., caused a rapid decrease in the rate of the denervated heart from 160-240 to about 40-60 beats/ min. This was followed by a peculiar periodic rhythm characterized by phases of complete absence of electrical and mechanical activity alternating with phases of apparently normal sino-auricular activity. After an inactive phase, the frequency (90-140 beats/mm.) was higher than that of the regular rhythm immediately before the onset of the periodic rhythm but declined to 50-70 beats/ min. prior to the next inactive phase. This cycle of activity and inactivity recurred at regular intervals for ten to thirty minutes, the inactive phases becoming progressively shorter and the active ones longer. Eventually, the periodic rhythm was replaced by a slow, but regular, rhythm of about 60-80 beats/min.

During the first few minutes after the administration of veratramine, infusion of epinephrine or norepinephrine, or stimulation of the postganglionic cardioaccelerator fibers, either reduced the number of inactive phases and prolonged the active phases, or changed the periodic rhythm to a regular rhythm. However, when the periodic rhythm had just given way to a regular rhythm, at a later stage of the action of veratramine, infusion of the amines, or stimulation of the accelerator nerves nearly always caused the periodic rhythm to return.