Blocking effects of cycleanine dimethobromide on nerve ganglia and neuromuscular junctions

Cycleanine is an active principle from Stephania epigeae H. S. Lo. The potencies of the blocking effects of its derivative, cycleanine dimethobromide, were studied on the transmission of the impulses through isolated rabbit supracervical sympathetic ganglia and rat phrenic nerve-diaphragm preparations in comparison with those of d-tubocurarine. The relative potency of ganglionic blocking effect of this drug was found to be 28.5% of that of d-tubocurarine. As to the muscle relaxant effect, this value was only 2.3%. The EC50 values for the ganglion blocking and muscular relaxant actions of d-tubocurarine were found to be 15.3 microg/ml and 1.1 microg/ml, respectively; while those of cycleanine were 58 microg/ml and 46 microg/ml. The results show that the muscular relaxant action of cycleanine is much more weaker than d-tubocurarine. This is consistent with the clinical report that cycleanine might preferably be used in controlled hypotension during surgical operation rather than as a muscular relaxant.