Properties of ginseng saponin inhibition of catecholamine secretion in bovine adrenal chromaffin cells

Abstract

To investigate the relationship between the inhibitory effects of ginseng saponins (ginsenosides) on acetylcholine-evoked secretion of catecholamines and the structures of ginsenosides, we examined the effects of ginsenoside-Rg 3 and -Rh 2, which are panaxadiol saponins, 20( R)- and 20( S)-ginsenoside-Rg 2, which are epimers involving the hydroxyl group at C-20 of sapogenin, and other plant saponins on the acetylcholine-evoked secretion of catecholamines from cultured bovine adrenal chromaffin cells. The ginsenoside-Rg 3 (1–100 μM) and -Rh 2 (10–100 μM) greatly reduced the acetylcholine-evoked secretion in a concentration-dependent manner comparable to that of ginsenoside-Rg 2, a panaxatriol saponin, which was the most potent inhibitor in our previous study. 20( R)- and 20( S)-ginsenoside-Rg 2 (1–100 μM) similarly reduced the acetylcholine-evoked secretion. In contrast, saikosaponin-a, glycyrrhizin and the cardiac glycosides (100 nM–100 μM), digitoxin and digoxin, had no significant inhibitory effect on catecholamine secretion. Saikosaponin-c (10–100 μM), however, had an inhibitory effect, which was less than that of ginsenoside-Rg 2 and -Rg 3. These results strongly suggest that the inhibitory effects of ginsenosides on the acetylcholine-evoked secretion of catecholamines from bovine adrenal chromaffin cells are a unique property of ginseng. Further, the relationship between the inhibitory effects and the structures of ginsenosides is discussed.