Pharmacological studies on 6-amino-2-fluoromethyl-3-(O-tolyl)-4(3H)-quinazolinone (afloqualone), a new centrally acting muscle relaxant. (II) Effects on the spinal reflex potential and the rigidity.

Effects of afloqualone on mono- (MSR) and poly-synaptic reflex (PSR) potentials and alpha- and gamma-rigidities were studied in experimental animals. Afloqualone dose dependently inhibited both MSR and PSR potentials in spinalized cats though afloqualone had no inhibitory effect on the patellar reflex in cats as reported in the previous paper. Afloqualone, like tolperisone, more selectively inhibited the PSR potential than MSR potential, whereas baclofen inhibited them in reverse order. However, the selectivity towards the PSR potential was higher with afloqualone than with tolperisone. In rats and cats, afloqualone dose dependently relaxed both alpha- and gamma-rigidity when administered p.o. as well as i.v. Its 50% inhibitory dose for alpha-rigidity was 1.5-2 times larger than that for gamma-rigidity. Tolperisone also relaxed both rigidities in i.v. administration, but had little effect when given p.o. Only mephenesin relaxed the post-ischaemic spinal rigidity in cats. These results suggest that afloqualone, like other well known centrally acting muscle relaxants except for baclofen, more strongly inhibits the polysynaptic pathway than the mono-synaptic pathway of the spinal cord as well as more strongly the gamma-system than the alpha-system.