A comparison of skeletal, cardiac, and smooth muscle actions of dantrolene sodium--a skeletal muscle relaxant.

Dantroline sodium, a skeletal muscle relaxant, has been proposed to inhibit the relase of Ca++ from the sarcoplasmic reticulum. Such a mechanism suggests that other muscle contractile systems operating with the same Ca++ denominator should also be affected by the drug. In the present studies dantrolene sodium effects on smooth, cardiac and skeletal muscle have been evaluated with in situ and in vitro techniques. In anesthetized dogs in situ skeletal muscle contractions were inhibitied in a dose-dependent manner, but cardiac muscle contractions were not. Effects on intestinal smooth muscle responses were highly variable and of short duration. In vitro, ED50 values were developed with dantrolene sodium (0.15-120 mg/l) in DMSO for each tissue. Skeletal muscle was the most sensitive (ED50 = 4.1 mg/l), cardiac muscle contractions were not inhibited by the drug and intestinal smooth muscle (ED50 = 59.0 mg/l) was approximately 1/14 as sensitive as skeletal muscle. It is concluded that skeletal muscle is uniquely sensitive to dantrolene sodium. A hypothesis for this specific action is offered.