PHARMACOLOGICAL PROPERTIES OF NK433, A NEW CENTRALLY ACTING MUSCLE-RELAXANT

The pharmacological properties of NK433 3-(1-pyrrolidinyl)-4'-trifluor omethylpropiophenone monohydrochloride), a novel muscle relaxant, were investigated. NK433 inhibited intercollicular decerebrate rigidity (g amma-rigidity) and anemic decerebrate rigidity (alpha-rigidity) dose d ependently. NK433 was stronger in inhibiting gamma-rigidity than alpha -rigidity. NK433 inhibited the increase in muscle spindle discharges i nduced by pinna pinching (gamma-activity) without affecting muscle spi ndle discharges or neuromuscular transmission. At muscle relaxant dose s in decerebrate rigidities, NK433 did not affect the muscle tone indu ced by morphine-HCl nor that of normal animals. These results suggest that NK433 selectively depresses the excessive muscle tone of decerebr ate rigidities through its effects on the central nervous system, and inhibition of gamma-activity causes a preferential depression of gamma -rigidity in comparison to alpha-rigidity. In i.v. experiments, the ef fects of NK433 on decerebrate rigidities were similar to those of eper isone-HCl and tolperisone-HCl, but in p.o. experiments, NK433 was at l east 3 times as potent as eperisone-HCl and tolperisone-HCl.