Incarvillea sinensis LAM. (Bignoniaceae) is a wild plant distributed in the northern area of China, and dried whole plants have traditionally been used in treating rheumatism and relieving pain as an ancient Chinese crude drug designated "Tougucao". 1) In the course of our investigations of its antinociceptive substances, a number of novel monoterpene alkaloids and macrocyclic spermine alkaloids have been characterized. [2][3][4][5][6][7][8][9] One of the monoterpene alkaloids, incarvillateine (INCA, Fig. 1), demonstrated a significant antinociceptive effect against the mouse pain model induced by formalin. We also reported the antinociceptive effect of INCA and comparison of its action with morphine (MOR). In comparison with antinociceptive effects of different doses of INCA and MOR, the ED 50 values of INCA were about 1.06 (early phase) and 1.33 (late phase) times lower than those of MOR. In addition, the antinociceptive effect of INCA in early phase was partially antagonized by pretreatment with naloxone (a narcotic antagonist, 5 mg/kg, s.c), while the effect of morphine was completely reversed. These results suggested the possibility that the action of INCA was partially related to its influence on the central opioid pathways.10) However, details on the pharmacological aspect of the mechanism have not, to our knowledge, been undertaken.In order to examine the antinociceptive mechanism, some opiate antagonists and adenosine receptor antagonist were administered to mice prior to incarvillateine injection in a formalin test, and the licking time of their pain reaction (paw licking) was measured.
MATERIALS AND METHODSChemicals INCA was prepared according to the previous report.2) Nor-binaltorphimine (nor-BNI) and b-funaltrexamine (b-FNA) were purchased from Tocris Cookson (Bristol, U.K.). Naltrindole (NTI) was obtained from Sigma (St. Louis, U.S.A.). Theophylline (THEO) and Tween 80 (polyoxyethylene sorbitan monooleate) were obtained from Nacalai Tesque (Kyoto, Japan). Ringer solution was purchased from Fuso Pharmaceutical (Osaka, Japan).Formalin Test This method represented a modification of that described by Dubuisson and Dennis.11) Male ddy mice (25Ϯ5 g) were used. The tested drugs were prepared as suspensions with 0.5% Tween 80/saline. Since the test has a biphasic pain response with two peaks, from 0 to 10 min (early phase) and from 10 to 30 min (late phase), the time spent licking the injected paw was recorded and the data were expressed as total licking time in the early phase and late phase.
Treatments of AntagonistsThe experiments were performed according to a modified method described by Kamei et al. 12) and Santos et al. 13) In measurement of the early phase, b-FNA (40 mg/kg, s.c) and nor-BNI (20 mg/kg, s.c) were administered 24 h before the inducer treatment, while NTI (0.5 mg/kg, s.c) and THEO (5 mg/kg, s.c.) were treated 10 min prior to the inducer injection.In measurement of the late phase, b-FNA and nor-BNI were administered 24 h before the inducer treatment. NTI and THEO were administered at ...