Pharmacological properties of the new centrally acting muscle relaxant (R)-(+)-3-phenyl-5-[2-(1-pyrrolidinylmethyl)butyryl]isoxazole hydrochloride.

The pharmacological properties of (R)-(+)-3-phenyl-5-[2-(1-pyrrolidinylmethyl)butyryl]isoxazole hydrochloride (CAS 144576-50-1, MS-322), a new centrally acting muscle relaxant, were investigated and compared with those of eperisone-HCl (CAS 56839-43-1) in experimental animals. MS-322 (1.5-6 mg/kg i.v.) reduced both anemic and intercollicular decerebration-induced rigidity in rats. Similar doses were required for these effects. The activity of MS-322 (200 mg/kg p.o.) against intercollicular decerebration-induced rigidity was greater and longer lasting than that of the same dose of eperisone-HCl. MS-322 (0.75-6 mg/ kg i.v.) inhibited the flexor reflex in anesthetized cats in a dose-dependent manner and more strongly than eperisone-HCl. MS-322 had no effect on the neuromuscular junction in anesthetized rats. The muscle relaxant activity of MS-322 in mice, demonstrated by the traction and rota-rod tests was stronger than that of eperisone-HCl, whereas MS-322 affected spontaneous motor activity in mice less than eperisone-HCl. The results of this study suggest that MS-322 is a potent centrally acting muscle relaxant with relatively weak depressant activity at other central nervous system pathways.