Synergistic Effects of Serotonin or Dopamine Combined With Lidocaine at Producing Nociceptive Block in Rats.

Background: The purpose of this experiment was to investigate the interactions of the local anesthetic lidocaine combined with an agent (serotonin or dopamine) as infiltrative anesthetics. Methods: Cutaneous analgesia was characterized by the blockade of the cutaneous trunci muscle reflex following 6 skin pinpricks on the rat back. Serotonin or dopamine at producing cutaneous analgesia in a dosage-dependent fashion was compared with lidocaine. Drug-drug interactions were calculated using the isobolographic analysis. Results: We revealed that serotonin, dopamine, and lidocaine provoked dose-related cutaneous analgesic effects. On the 50% effective dose basis, the rank of drugs' potency was found to be serotonin (1.70 [1.56-1.85] [mu]mol) > lidocaine (5.18 [4.67-5.75] [mu]mol) > dopamine (43.0 [40.9-45.2] [mu]mol) (P

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