The present study was attempted to compare ginsenoside-Rb2 (Rb2) one of panaxadiol saponins with Ginsenoside-Rg2 (Rg2), another panaxadiol saponin in the inhibitory effects on the secretion of catecholamines (CA) from the perfused model of the rat adrenal gland.Design and Method:
The adrenal gland was isolated and perfused with Krebs-bicarbonate. CA was measured directly by using the fluorospectrophotometer.Results:
Both Rb2 and Rg2 during perfusion into an adrenal vein for 90 min inhibited the CA release evoked by ACh, angiotensin II, DMPP, high K+, and McN-A-343 in a time-dependent manner. Also, in the presence of Rb2 or Rg2, the CA release evoked by veratridine (an activator of voltage-dependent Na+ channels), Bay-K-8644 (a voltage-dependent L-type Ca2+ channel activator), and cyclopiazonic acid (a cytoplasmic Ca2+-ATPase inhibitor) were significantly reduced. Both two ginsenosides also greatly induced NO release from adrenal medulla. Based on the same concentration of Rb2 and Rg2, for the CA release evoked by ACh, high K+, DMPP, McN-A-343, Ang II, veratridine, Bay-K-8644 and cyclopiazonic acid, as well as for No release, the following rank order of inhibitory potency was obtained: Rg2> Rb2. In the simultaneous presence of fimasartan, an antagonist of angiotensin II receptors and Ginsenoside-Rg2, ACh- or angiotensin II-evoked CA secretion was more strongly inhibited compared with that of fimasartan- or Rg2-treated alone.Conclusions:
Collectively, these results demonstrate that both Rb2 and Rg2 can inhibit the CA secretion evoked by activation of both cholinergic and AT1 receptors stimulation from the perfused rat adrenal medulla. When these two ginsenosides were used in combination with a different antihypertensive agent, antihypertensive effects were enhanced, which may also be of clinical benefit. Based on concentrations used in this study, the inhibitory effect of ginsenoside-Rg2 on the CA secretion seems to be more potent than that of ginsenoside-Rb2.