The influence of urea on nervous stimulation of cardiac muscle

Summary

A study was made of the effect of urea on regeneration in cardiac muscle. Urea was chosen because according to results obtained by Kh. S. Koshtoyants, this substance promotes the liberation of free sulfhydryl groups from the protein molecule, and so plays an important part in the oxidation-reduction processes in the tissues, and in neurohumoral regulation.

The experiments reported here were carried out on isolated frog hearts, and the sympathetic and vagus nerves were retained for stimulation. Blood pressure and fluctuations in pulse amplitude were recorded in acute experiments on dogs. Usually, the vagosympathetic or sympathetic nerves were first stimulated by current from an induction coil. A study was then made of the specific features of the effect exerted by these nerves on an isolated frog heart perfused by 0.5–1% urea solution, or on the heart of an intact animal which was given an intravenous injection of 20–40% urea solution. In evaluating these results, attention was paid to the frequency and amplitude of the cardiac contractions, and in dogs to the blood pressure and pulse pressure. Perfusion of the isolated frog heart with 1–2 ml of 0.5 or 1% urea solution caused transient changes in both the amplitude and the rate of the heart beat, but intravenous injection of 0.5–1 ml per kg of 20–40% urea solution caused no significant drop in blood pressure but produced a rise in the amplitude of the pulse pressure. Treatment with urea considerably intensified the effect of stimulation of the cardiac sympathetic and vagosympathetic nerves.