[Effects of muscle relaxant E-0646 on human stretch reflex and responses]

The experiment examined the effects of a muscle relaxant E-0646 on short latency stretch reflex (SLR) and long latency stretch responses (LLRs) of lower leg muscles in 5 healthy male subjects, aged 24-41 years. An AC servomotor produced an ankle rotation of comfortably seated subjects in the direction to stretch the triceps surae muscle for the SLR and the tibialis anterior muscle for the LLRs. Following control measurements, after the oral administration of 50, 100, 150, and 300 mg of E-0646, the SLR and LLRs were recorded every 2 hours for 4 or 6 hours with simultaneous blood sampling to measure E-0646 plasma levels. Electromyograms (EMGs) of the soleus and tibialis anterior muscles were recorded with surface electrodes on each muscle belly. A precision potentiometer was used to measure the ankle angle. The soleus SLR, evoked by a torque pulse (7 msec duration) of one of 5 different amplitudes, decreased 2 hours after the 300 mg administration. A SLR decrease was also found in a simple relationship between the integrated SLR EMG and the angular velocity at 20 msec after the torque onset, in which the slope and intercept of the relationship changed. The plasma E-0646 level roughly correlated with the SLR decrease. No significant change of the SLR was observed when dosage was less than 150 mg. The LLRs of the tibialis anterior muscle were tested under the instruction "resist when perturbed" during a weak isometric contraction against a constant plantar flexion torque.(ABSTRACT TRUNCATED AT 250 WORDS)