Effect of urea on the mechanical and electrical activity of the perfused rat heart.

The mechanical and electrical activities of Langendorff perfused isolated hearts from albino female rats were studied before and after the addition of 17 mM urea to the medium. The effect of urea on the osmolarity of the perfusing solution was evaluated by also carrying out the measurement in 17 mM saccharose. The rate of the spontaneously beating hearts did not change after urea or saccharose treatment. However, urea promoted a decrease in the left ventricle isovolumic systolic pressure and a reduction of the total QRS amplitude. Saccharose did not alter mechanical or electrical characteristics. Although the concentration of urea which reduced systolic isovolumic pressure development and altered the ECG is well below that required to modify protein conformation in vitro, our results suggest that its action could be at the sarcolemmal level.