Exercise produces sensitivity to metocurine

Abstract

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 by 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 analyis 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 estimated in the effect compartment which produced 50% paralysis was 0.114 ± 0.008 μg·ml-1 (mean ± SD) in exercised dogs and 0.189 ± 0.038 μg·ml-1 in nonexercised dogs, which was significant at P < 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.