Involvement of cannabinoid CB1 receptors in the antinociceptive effect of dipyrone.

Cannabinoid CB1 receptors have been implicated in the antinociceptive effect of paracetamol. In the current study, we examined whether blockade of CB1 receptors prevent the analgesic activity of dipyrone, in a similar way to paracetamol. Hot-plate and tail-flick tests were used to assess the antinociceptive activity in mice. Dipyrone and WIN 55,212-2, a cannabinoid agonist, exerted significant antinociceptive effects in both hot-plate and tail flick tests. The CB1 receptor antagonist, AM-251 (3 mg/kg), at a dose which had no effect when used alone, did not alter the antinociceptive effect of dipyrone, whereas completely prevented the antinociceptive activity of WIN 55,212-2 in both thermal antinociceptive tests. Our findings suggest that, unlike paracetamol, cannabinoid CB1 receptors do not participate in the antinociceptive action of dipyrone when acute pain tests used.