Antinociceptive effects of (+)-matrine in mice

The antinociceptive potency of matridin-15-one ((+)-matrine) was examined using the acetic acid-induced abdominal contraction test and the tail-flick test in mice. (+)-Matrine, at doses of 1 to 10 mg/kg, s.c., produced a marked and dose-dependent inhibition of the number of acetic acid-induced abdominal contractions in mice. The antinociceptive effect of (+)-matrine in the acetic acid-induced abdominal contraction test in mice was identical to that of pentazocine. Indeed, there was no significant difference in the ED 50 (mg/kg with 95% confidence limits) values for the inhibition of acetic acid-induced abdominal contractions between (+)-matrine (4.7 (4.1–5.3)) and pentazocine (3.3 (2.2–5.0)). Furthermore, in the tail-flick assay, (+)-matrine at doses of 10 and 30 mg/kg, s.c., again produced a dose-dependent antinociceptive effect. When nor-binaltorphimine (20 mg/kg, s.c.), a selective κ-opioid receptor antagonist, was administered 3 h before treatment with (+)-matrine, the antinociceptive effect of (+)-matrine was markedly antagonized. Furthermore, the antinociceptive effect of (+)-matrine was partially antagonized by pretreatment with β-funaltrexamine, a selective μ-opioid receptor antagonist. Naltrindole, a selective δ-opioid receptor antagonist, had no effect on the antinociceptive effect of (+)-matrine. In conclusion, (+)-matrine produced an antinociceptive effect mainly through the activation of κ-opioid receptors and partially through μ-opioid receptors.