Exercise produces sensitivity to metocurine

Chronic muscle disuse decreases the sensitivity of skeletal muscle to nondepolarizing relaxants, such as metocurine (MTC). In this study, the authors determined whether chronic conditioning would produce the opposite effect and increase the sensitivity of skeletal muscle to MTC. Five dogs were exercised by daily running over a period of 5 weeks. At the conclusion of this training period, a pharmacokinetic and pharmacodynamic study of the MTC dose-response relationship was performed. The same analysis was performed on four dogs housed in the same kennel who did not undergo conditioning. Neuromuscular blockade was measured and recorded bilaterally in both gastrocnemius muscles while the animal was anesthetized with nitrous oxide and pentobarbital, 30 ml.kg-1. Plasma concentrations of MTC were measured by radioimmunoassay. The MTC concentration estimated in the effect compartment which produced 50% paralysis was 0.114 +/- 0.008 micrograms.ml-1 (mean +/- SD) in exercised dogs and 0.189 +/- 0.038 micrograms.ml-1 in nonexercised dogs, which was significant at P less than 0.005). The MTC concentration versus response curves were parallel. This supports the authors' hypothesis that exercise increases sensitivity to the nondepolarizing muscle relaxant metocurine.