kappa-Opioid receptor-mediated antinociceptive effects of stereoisomers and derivatives of (+)-matrine in mice.

The antinociceptive effects of seven matrine-type lupin alkaloids were examined using the acetic acid-induced abdominal contraction test (the writhing test) and the tail-flick test in mice. (+)-Allomatrine, the C-6 epimer of (+)-matrine, produced the antinociceptive effect at 1/3 potency of (+)-matrine or pentazocine. It was demonstrated that the antinociceptive effects of (+)-allomatrine were mediated through the activation of kappa-opioid receptors, while the antinociceptive effect of (+)-matrine was mediated by both mu- and kappa-opioid receptors. (-)-Sophoridine, the C-6 epimer of (+)-matrine, (+)-sophoranol, (-)-14 beta-hydroxymatrine and (+)-matrine N-oxide, which possess a hydrophilic group, and (-)-sophocarpine and (-)-sophoramine having a double bond(s) did not show significant antinociceptive activity.