The effects of dantrolene sodium on cardiac and skeletal muscle in rats.

Dantrolene sodium in different concentrations was administered to the spontaneously beating heart placed in a modified Langendorff apparatus. Heart frequency and contractility were recorded. Dantrolene sodium was also administered to the rat diaphragm. Twitch tension after indirect supramaximal stimulation was recorded. Dantrolene sodium produced a long lasting dose-dependent reduction of the contractility of the isolated rat heart up to 75% of control values. It had no effect on the heart frequency. The drug also decreased the force of contraction of the rat skeletal muscle in vitro to the same extent. The diaphragm appeared to be more sensitive to low concentrations of dantrolene sodium than was heart muscle i.e. the dose-response curve on rat diaphragm was flatter. It may be concluded however that higher concentrations of dantrolene sodium may effect the contractility of heart muscle as well and that this may have clinical implications.