EFFECT OF EPHEDRINE ON MUSCLE WEAKNESS IN A MODEL OF MYASTHENIA-GRAVIS IN RATS

In addition to therapy with anticholinesterases, ephedrine is sometime s used to improve muscle strength in myasthenia gravis, with variable results. The efficacy of ephedrine was tested in rats with a alpha-bun garotoxin-induced model of myasthenia gravis. The rats showed a droopi ng lower lip and impaired capability of drinking. Injections of neosti gmine caused an improvement of the position of the lip. Ephedrine caus ed some improvement. However, ephedrine had no effect, either on the l ower lip or on water consumption, when the sleep-wake cycle was revers ed and the rats had their active period during day time. It was conclu ded that the effect of ephedrine was unspecific and probably due to ar ousal from drowsiness. The results suggest, therefore, that the variab ility of the effect of ephedrine in myasthenic patients is unrelated t o neuromuscular transmission per se but rather due to a difference in susceptibility to arousal.