Abstract

A spontaneously beating isolated preparation of guinea-pig right atrium is described.

Veratramine, 0.05 to 0.8 µg/ml, has an atropine-resistant negative chronotropic action on the preparation.

Veratramine, in the same concentrations, has a similar action on preparations previously accelerated with epinephrine. The antagonism between the two drugs appears to be physiological, epinephrine increasing the rate, veratramine causing slowing.

Prolonged contact with moderate or large doses of veratramine, particularly in the presence of epinephrine, gives rise to periodic rhythms.