Effects of a single methylprednisolone dose on a facilitatory response of mammalian motor nerve.

Long-term glucocorticoid dosing directly enhances a facilitatory function of cat soleus motor nerve terminals. Posttetanic potentiation (PTP) of soleus contraction is a manifestation of this prejunctional facilitation. The present study demonstrates that the same enhancement of facilitation is produced with a single large intravenous dose methylprednisolone. The single dosing method, however, showed an initial suppression of facilitation that neared recovery in four hours. Thereafter, the characteristic augmentation of prejunctional facilitation emerged, peaking in 24 hours. Return to control required four days. Knowledge of this time course enabled centrally disconnected motor nerve endings to be identified as the site of both phases of the steroid action. Since the neuromuscular facilitation studied is equivalent to that triggered by neostigmine-like drugs, the results infer that the antimyasthenic effect of glucocorticoids may involve a direct action on motor nerve endings.