Effect of corticosteroids on sciatic nerve-tibialis anterior muscle of rats treated with hemicholinium-3. An experimental approach to a possible mechanism of action of corticosteroids in myasthenia gravis.

We studied the effect of intraperitoneally administered corticosteroids on the neuromuscular transmission in the sciatic nerve-tibialis anterior muscle preparation of the anesthetized rat stimulated at a rate of 10 Hz. Administered simultaneously with hemicholinium-3 (HC-3), 80 mug per kilogram (that is, half the lethal dose for 50 percent survival), prednisolone and dexamethasone cause a marked reversal of the block of the neuromuscular transmission caused by HC-3. The effect of aldosterone is very small. The blocking action of d-tubocurarine is not antagonized by either prednisolone or dexamethasone. Choline provides total protection against the HC-3 blockade, whereas physostigmine, in a just sublethal dose, is ineffective. We tentatively conclude that in myasthenia gravis the carrier-mediated transport of choline into the nerve endings may be deficient and that the beneficial effect of corticosteroids in this condition is based on their ability to ameliorate the deficient choline transport.