Effects of long-term administration of ambenonium chloride on motor end-plate fine structure and acetylcholine receptor in rat.

Ambenonium chloride was administered orally in a dosage of 6 mg/kg/day to rats for 14-360 days. Motor end-plate fine structure and junctional AChR were quantitatively analyzed and red (soleus) and white (EDL) muscle fibers. In treated animals, degeneration and simplification of postsynaptic folds and widening of synaptic clefts were often observed in soleus end-plates, but infrequently in EDL end-plates. On the other hand, the postsynaptic AChR was reduced markedly in both soleus and EDL end-plates. No presynaptic changes were observed. These results show that long-term administration of Anti-ChE agents in myasthenia gravis may have an adverse effect on neuromuscular transmission.