Demoor's Active Substance of the Heart

Abstract

Demoor^{1, 2} has described a humoral regulatory substance elaborated by the nodal tissue of the heart which has the property of conferring rhythmicity upon the aperiodic beat of an isolated left auricle. His theory is based chiefly upon the observation that the right auricle of the rabbit or guinea pig, excised and dropped into a Ringer-Locke solution, soon assumes a regular rhythm; the left auricle, however, gives only aperiodic, jerky beats in this solution. If now, the solution in which the right auricle has been active for a while is poured over the left auricle, the latter gives rhythmical beats. Demoor has prepared both saline and alcoholic extracts of the right auricle of the rabbit which were able to confer periodicity upon the isolated left auricle of the rabbit. He has named this unknown substance the “active substance” of the heart. The writers have been able to confirm his observations.

All solutions used in the experiments were made from Baker's analyzed chemicals, recrystallized. The Ringer-Locke solution employed consisted of NaCl 0.9%, CaCl₂ 0.024%, KCl 0.042%, NaHCO₃ 0.01%, and Dextrose 0.1%. The pH was adjusted to 7.4, and the solution was oxygenated and maintained at a temperature of 37°C. throughout the experiment. An adult rabbit was placed under light ether anesthesia, the heart was exposed and perfused through the ascending vena cava with the Ringer-Locke solution for a short time to free the heart of blood. The heart was then excised and both auricles removed, care being taken to see that the venous openings were included in each preparation and that the left auricle was wholly free of septum. Each auricle was then placed in a few cc.'s of the warmed Ringer-Locke solution.