[A comparison of the effects of baclofen and some other muscle relaxants on alpha-rigidity in rats].

Muscle relaxant effects of baclofen were compared with those of dantrolene, diazepam, chlordiazepoxide and tolperisone. When administered intraduodenally (i.d.), baclofen and dantrolene but not diazepam suppressed the sustained rigidity of forelimbs in anemically decerebrated rats, and ED50 values of the former two drugs were 2.9 and 22 mg/kg, respectively. Baclofen, dantrolene and diazepam reduced the phasic rigidity of the decerebrated animals induced by mechanical stimulation of hindlimbs, with their respective ED50 values of 6.2, 140 and 1.4 mg/kg, i.d. Both the rigidities were almost insensitive to chlordiazepoxide and tolperisone. With the exception of tolperisone, these drugs also produced a muscle relaxation in intact animals as measured by traction (rats), rotarod (mice), and grip-strength (mice) tests. ED50 or eD25 values were calculated to be in the following ranges: 5.6 approximately 12 mg/kg, p.o. for baclofen, 15 approximately 35 mg/kg, p.o. for dantrolene, 2.1 approximately 6.5 mg/kg, p.o. for diazepam and 33 approximately 64 mg/kg, p.o. for chlordiazepoxide. These results suggest that baclofen, unlike other drugs, may be effective in reducing both tonic and phasic rigidities at lower doses than those causing muscle relaxation in intact animals.