[Possible participation of lactic acid in formation of a non-mediator agent stimulating the heart during exposure of the myocardium to sympathetic influences].

Release of A-factor, the physiologically active substance of a non--mediatory nature under sympathetic stimulation, depends upon the glycolytic process. To examine the assumption that A-factor may be a glycolytic product, lactic acid was studied in particular, and it was shown that A-factor is not identical to lactic acid. However it was found out that lactic acid participates in the release of A-factor in the heart. It was shown that under the effect of lactic acid a substance having high cardiostimulating activity was released in the frog heart muscle. This cardiostimulating substance as well as A-factor increases the amplitude of contractions of A-factor, was not abolished with beta-sympathicolytic inderal. The ability of both substances to stimulate heart activity was preserved after 20 min heating in a water bath. The cardiostimulating substance similar to A-factor increases heart sensitivity to sympathetic and decreases it to parasympathetic stimulations. It may be suggested that the cardiostimulating substance released in the heart under the effect of lactic acid is identical to A-factor released in the myocardium under the action of catecholamines and stimulation of the sympathetic nerve.