Neuromuscular blocking activity of alkaloids of Cyclea hainanensis

The neuromuscular blocking activity of 4’’-o-methyl-d-curine and dl-curine isolated from Cyclea hainanensis in Hai-nan Island were studied. It was found that the dimethyl dl-curine dimethochloride was 1-2.5 times more active than d-tubocurarine in conscious rabbits,cats and dogs,while 4’’-o-methyl-d-curine dimethiodide was less potent than d-tubocurarine.Dimethyl dl-curine dimethochloride. Dimethyl dl-curine dimethochloride and 4’’-o-methyl-d-curine dimethiodide had a non-depolarizing mode of action.In contrast to d-tubocurarine,its ganglion-blocking potency and histamine-releasing properties were weak. Hence the side effect of hypotension seen with d-tubocurarine was less severe than that with dimethyl dl-curine dimethochloride and 4’’-o-methyl-d-curine dimethiodide. In mice and rats dimethyl dl-curine dimethochloride and 4’’-o-methyl-d-curine dimethiodide exhibited a higher therapeutic index than d-tubocurarine.