Impact of ginsenoside-Rg3 on catecholamine secretion in the perfused model of the rat adrenal medullae

Abstract

Background: The present study was the first attempt to explore the characteristics of ginsenoside-Rg3 (Rg3) on release of catecholamines (CA) in the perfused rat adrenal medullae and also to verify the underlying action mechanism. Materials and Methods: The adrenal medulla was separated by some modification of the previous method and perfused with Krebs solution. CA was assayed directly by the fluorometry. Results: Rg3 reduced acetylcholine (ACh)-produced CA release in a dose- and time-dependent manner. Rg3 time-dependently depressed CA release produced by 3-(m-chloro-phenyl-carbamoyl-oxy)-2-butynyltrimethyl ammonium chloride (McN-A-343), 1,1-dimethyl-4-phenyl piperazinium iodide, and angiotensin II. In the presence of Rg3, the CA release produced by high K+, veratridine, cyclopiazonic acid, and methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4- (2-trifluoromethyl-phenyl)-pyridine-5-carboxylate (Bay-K-8644) was also markedly suppressed. However, during the simultaneous perfusion of Rg3 and Nω-nitro-l-arginine methyl ester hydrochloride (l-NAME), the release of CA produced by ACh, angiotensin II, Bay-K-8644, and veratridine was restored closely to the level of each control, in contrast to that of Rg3-treatment alone. The nitric oxide (NO) release was significantly elevated by Rg3-treatment. Furthermore, in the coexistence of Rg3 and fimasartan, ACh-produced CA release was more significantly reduced as compared to that of fimasartan-treatment alone. Conclusions: We present the first evidence that Rg3 markedly depresses the CA secretion produced by activation of neuronal cholinergic and angiotensinergic receptors. Rg3-produced inhibition appears to be evoked not only by blocking the inflow of Na+ and Ca2+ into adrenomedullary cells but also by preventing the Ca2+ release from intracellular storage, partly through enhancement of NO release by NO synthase activation. Coadministration of Rg3 and fimasartan may be clinically beneficial for the treatment of cardiovascular diseases. Abbreviations used: Rg3: Ginsenoside-Rg3; VDCC: L-type voltage-dependent Ca2+ channels; Bay–K-8644: Methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethyl-phenyl)-pyridine-5-carboxylate; ACh: Acetylcholine; McN-A-343: 3-(m-chloro-phenyl-carbamoyl-oxy)-2-butynyltrimethyl ammonium; DMPP: 1.1-dimethyl-4-phenyl piperazinium; NO: Nitric oxide; L-NAME: Nω-nitro-l-arginine methyl ester; nNOS: Neuronal NO synthase.