Potentiation of electroacupuncture analgesia by l-tetrahydropalmatine and its analogues in rabbits

l-Tetrahydropalmatine (l-THP), tetrahydroberberine (THB) and l-stepholidine (l-SPD) are the homologues of tetrahydroproto berberines and have a common antagonistic effect to central dopamine receptors. In the present experiment, the potassium iontophoretic dolorimetry was used to determine the pain threshold of rabbits. Unilateral "Hegu" point (the dorsum of the front paw, between 1st and 2nd metacarpals) and "Waiguan" point (the dorsum of the foreleg, between radius and ulna, 2 cm above the wrist joint) of each rabbit were electrically needled. The effects of iv l-THP 8 mg/kg, THB 16 mg/kg or l-SPD 4 mg/kg on electroacupuncture analgesia were investigated. The experimental results indicated that these 3 agents enhanced the potency of electroacupuncture analgesia and prolonged the duration as well. This investigation gives the evidence that the drug possessing antagonistic effect to central dopamine receptors could be used as a synergist of acupuncture analgesia.