Jpn. J. Pharmacol. 71 (4), 345-349 (1996)

The Possible Involvement of GABAA Systems in the Antinarcotic Effect of Majonoside-R2, a Major Constituent of Vietnamese Ginseng, in Mice

Nguyen Thi Thu Huong (1), Kinzo Matsumoto (1), Kazuo Yamasaki (2), Nguyen Minh Duc (3), Nguyen Thoi Nham (3) and Hiroshi Watanabe (1,*)

(1) Division of Pharmacology, Research Institute for Wakan-Yaku (Oriental Medicines), Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-01, Japan (2) Department of Biological Active Substances, Institute of Pharmaceutical Sciences, Hiroshima University School of Medicine, Kasumi 1-2-3, Minami-ku, Hiroshima 734, Japan (3) The Science-Production Centre of Vietnamese Ginseng, Ho Chi Minh University of Medicine and Pharmacy, 41 Dinh Tien Hoang, District 1, Ho Chi Minh City, Vietnam (*) To whom all correspondence should be addressed.

Abstract: The effect of majonoside-R2 on morphine- and U-50,488H-induced antinociception was examined by the tail-pinch test in mice and compared with that of diazepam. Majonoside-R2 and diazepam inhibited the morphine- and U-50,488H-induced antinociception, and the actions were antagonized by the benzodiazepine receptor antagonist flumazenil and the GABA-gated Cl- channel blocker picrotoxin. Diazepam but not majonoside-R2 exhibited a protective activity against convulsion caused by the GABAA antagonists bicuculline and picrotoxin. These results indicate that GABAA systems are involved in the effect of majonoside-R2 on the opioid-induced antinociception and suggest that the mechanisms of action of majonoside-R2 may differ from those of diazepam.

Keywords: Majonoside-R2, Antinociception, GABAA-receptor

Copyright© The Japanese Pharmacological Society 1996

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