Increase of acetylcholine release by Panax ginseng root enhances insulin secretion in Wistar rats

The present study was designed to ascertain the effect of Panax ginseng root on plasma glucose and investigate the possible mechanisms for the effect. Ninety minutes after the oral administration of P. ginseng root to fasting Wistar rats, plasma glucose decreased in a dose-dependent manner. Simultaneous with the reduction in plasma glucose, an increase in the plasma level of insulin and C-peptide was also observed. Moreover, disruption of the available synaptic acetylcholine (ACh), using the inhibitor for choline uptake (hemicholinium-3), or the inhibitor for vesicular choline transport (vesamicol), abolished the metabolic actions of P. ginseng root. Conversely, physostigmine, at a concentration sufficient to inhibit acetylcholinesterase, enhanced the metabolic effect of P. ginseng root. It is possible that P. ginseng root mediates the release of ACh from nerve terminals to enhance insulin secretion. Blockade of the actions of P. ginseng root by 4-diphenylacetoxy-N-methylpiperdine methiodide (4-DAMP) suggested that the site of action is the muscarinic M3 receptor. Taken together, the results suggest that P. ginseng root has the ability to increase the release of ACh from nerve terminals in rats so as to stimulate muscarinic M3 receptors activity located in the pancreatic cells for the secretion of insulin, which in turn lower plasma glucose.