Bay K 8644 induces a reversible spasticity-like syndrome in rats.

The dihydropyridine Bay K 8644 exerts a positive modulation of Ca2+ channels. Administration of Bay K 8644 3-5 mg/kg i.p. to rats induces within 15 min a severe spasticity syndrome consisting of stiff tail, arched back, stretching and twisting of forelimbs and hindlegs and backwards motility and rolling over. The syndrome was effectively antagonized by nifedipine 3-30 mg/kg but not by the other Ca2+ channel blockers flunarizine, diltiazem and verapamil. Diltiazem even enhanced the spasticity. Diazepam 10-30 mg/kg i.p. completely blocked the spasticity whereas the other muscle relaxants (-)-baclofen and the beta-carboline ZK 93423 were completely inactive. These findings with Bay K 8644 suggest that spasticity may be caused by changed Ca2+ homeostasis.