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E Tachikawa, K Kudo, T Kashimoto and E Takahashi
Department of Pharmacology, School of Medicine, Iwate Medical University, Morioka, Japan.
The effects of various ginseng saponins (ginsenosides Rb1, Rb2, Rb3, Rc, Rd, Re, Rf, Rg1, Rg2, Rh1, Ro and Rs1), which are isolated from the root of Panax ginseng, on the catecholamine secretion from bovine adrenal chromaffin cells stimulated by ACh were examined. Most of the ginsenosides (1-100 microM) had a tendency to reduce the ACh-evoked secretion of catecholamines. The order of inhibitory potency (at the concentration of 10 microM) was as follows: Rg2 > Rf > Re > Rh1 > Rb2, Rg1 > Rb1 > Rc > Rb3, Rd, Ro, Rs1. The inhibition of ginseoside Rg2 at 10 microM was 72%, but ginsenosides Rb3, Rd, Ro and Rs1 did not show the inhibitory effect. On the other hand, ginsenoside Rg2 (1-100 microM) did not at all affect the secretion induced by high K+ or veratridine, a potent specific activator of voltage-sensitive Na+ channels. Ginsenoside Rg2 (1-100 microM) also inhibited both ACh- induced Na+ and Ca++ influxes into the cells in a concentration- dependent manner. The concentration-response curves for ginsenoside Rg2 inhibition of Na+ influx, of Ca++ influx and of catecholamine secretion were quite similar. The inhibitory effect of ginsenoside Rg2 on the secretion was not overcome by increasing ACh or external Ca++ concentrations. These results strongly suggest that the ginseng saponins, especially ginsenoside Rg2, block the nicotinic ACh receptors or the receptor-operated Na+ channels (but not voltage-sensitive Na+ and Ca++ channels), inhibit Na+ influx through the channels and consequently reduce both Ca++ influx and catecholamine secretion in bovine adrenal chromaffin cells.(ABSTRACT TRUNCATED AT 250 WORDS)
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