Synergistic effect of propranolol and quipazine on desipramine enhanced shock-elicited fighting in rats.

Changes in shock-elicited fighting (SEF) were measured following single or repeated injections (IP) of dl-propranolol (5 mg/kg, 20 mg/kg) or quipazine (1.25 mg/kg, 2.5 mg/kg) given either alone or in combination to saline or desipramine (DMI) (10 mg/kg) treated rats. DMI + propranolol (20 mg/kg) caused a greater increase in fighting than DMI + saline 18 hours after last dose. Propranolol (20 mg/kg) produced an equal inhibition in both of these groups at 15 min. Propranolol (5 mg/kg) had no effect. Quipazine (2.5 mg/kg) failed to alter DMI induced increase in SEF. The combination of propranolol (5 mg/kg) + quipazine (1.25 mg/kg) blocked the enhanced SEF significantly in DMI treated rats in comparison to DMI + saline treated group. This combination of propranolol + quipazine produced no significant change in SEF in saline treated group in comparison to the pretest level. These results suggested that propranolol + quipazine act synergistically at low doses to inhibit the increased SEF seen in DMI treated rats and might have therapeutic implications for the management of irritable aggression or mania.