Neuromuscular Blocking Action of Alkaloids from a Japanese Crude Drug “Shin-I” (Flos Magnoliae) in Frog Skeletal Muscle

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Abstract
From the dried buds of Magnolia salicifolia MAXIM, d-coclaurine (1), d-reticuline (2), 1-N-methylcoclaurine (3) and yuzirine (4) were isolated. Fifty percent inhibitory doses (µM) in acetylcholine (ACh, 27.5 µM)-induced contraction of frog skeletal muscle were as follows: d-tubocuraine (d-TC) 3.09, 2 93.2, 3 211, 1 467 and 4 more than 945. 4 (94.5 and 315 µM) increased the ACh-induced contraction. Indirectly stimulated twitching of frog nerve-muscle preparations were completely blocked by the following doses (µM): d-TC 1.47, 1 31.1, 2 239 and 3 more than 257. 1, 2 and 3 did not or only slightly block directly stimulated twitching. In contrast 271 µM 4 blocked the directly stimulated twitching.