Reflex arc of the teeth clenching-induced pressor response in rats
Dantrolene sodium, a peripherally acting skeletal muscle relaxant, at doses up to 30 mg/kg iv had no effect on respiratory volume, respiratory rate, blood pressure, or heart rate in anesthetized dogs. The ED50 for inhibition of skeletal muscle contractions was 4.5 mg/kg in anesthetized dogs. In anesthetized sheep, the ED50 for skeletal muscle relaxation was 3.2 mg/kg under methoxyflurane anesthesia and 1.7 mg/kg under pentobarbital anesthesia. Unanesthetized sheep administered doses up to 30 mg/kg iv evidenced no dose-related cardiovascular effects. Respiratory volume decreased and respiratory rate increased, with the net result that the respiratory minute volume was not affected by dantrolene sodium. The results indicate that dantrolene sodium has no effect on the cardiovascular or respiratory systems that would preclude its use intravenously in acute conditions where direct relaxation of skeletal muscle is required, as in the management of malignant hyperthermia.