A possible central antinociceptive effect of dipyrone in mice.

The antinociceptive effect of dipyrone, a nonsteroidal and inflammatory drug, was studied in a series of experiment employing tail-flick and hot-place models and the abdominal constrictor test. The drug was given via intracerebroventricular (i.c.v.), intrathecal (i.t.) or subcutaneous (s.c.) routes. Dipyrone exhibited no analgesic activity in the tail-flick and hotplate tests while it inhibited the number of stretches in a dose-dependent manner. The antinociceptive effect of dipyrone administered by the i.c.v. and i.t. routes was almost complete reversed by naloxone treatment. The same procedure attenuated but not completely inhibited the dipyrone action induced by s.c. administration. Histopathological examination revealed that i.t. dipyrone application produces no significant lesion in the spinal cord. The results suggest that dipyrone may exert a central antinociceptive action reversed by naloxone.