Release of acetylcholine by Die-Huang-Wan to enhance insulin secretion for lowering plasma glucose in Wistar rats

We have recently observed that Die-Huang-Wan has an ability to stimulate the secretion of insulin to decrease the plasma glucose levels in normal rats. In the present study, this effect of Die-Huang-Wan was reversed by the general muscarinic antagonists atropine and scopolamine, but not affected by the ganglionic nicotinic antagonist pentolinium or hexamethonium. Moreover, disruption of synaptically available acetylcholine using an inhibitor of choline uptake, hemicholinium-3, or vesicular acetylcholine transport, vesamicol, abolished the actions induced by Die-Huang-Wan. Mediation of acetylcholine released from nerve terminals by this product can thus be considered. Also, physostigmine at concentration sufficient to inhibit acetylcholinesterase enhanced the effect of Die-Huang-Wan. Blockade of the increase of plasma insulin and plasma glucose lowering action of Die-Huang-Wan by 4-diphenylacetoxy-N-methylpiperdine methiodide (4-DAMP) indicated the mediation of muscarinic M3 receptors. The results suggest that Die-Huang-Wan may enhance the release of acetylcholine from nerve terminals to stimulate the muscarinic M3 receptors for augmenting insulin release to produce plasma glucose lowering action.