Participation of the sympathetic system in acetic acid-induced writhing in mice

We investigated the participation of a sympathetic component in the abdominal contortions induced by intraperitoneal injection of 0.6% acetic acid in the mouse. The beta blocker propranolol (4 mg/kg, sc) caused a small significant (19%) blockade of the contortions but strongly potentiated (greater than 80%) the effect of indomethacin (30% at 5 mg/kg, sc). Significant inhibition of writhing was also observed with sympatholytics such as guanethidine (27% at 30 mg/kg, sc) and by a specific dopamine-I antagonist, SCH 23390 (62% at 400 micrograms/kg, sc). Tyramine, which releases sympathomimetic amines, and cocaine, which partially blocks the uptake of amines, potentiated acetic acid writhing. Intraperitoneal administration of noradrenaline (187 micrograms/kg)potentiated acetic acid-induced writhing. These results are consistent with the suggestion of Nakamura and Ferreira (1) that inflammatory nociception has a dual component: one mediated by cyclooxygenase metabolites and another by sympathetic amines, possibly acting through a DA-1 type receptor.