DL-TETRAHYDROPALMATINE-PRODUCED HYPOTENSION AND BRADYCARDIA IN RATS THROUGH THE INHIBITION OF CENTRAL NERVOUS DOPAMINERGIC MECHANISMS

The effects of DL-tetrahydropalmatine (THP; a main active substance of the Chinese herb corydalis), haloperidol (a dopamine D-2 receptor antagonist), apomorphine and amphetamine on cardiovascular function and striatal dopamine (DA) release were compared in rats under general anesthesia. Intravenous administration of THP (1-10 mg/kg) or haloperidol (0.5-1.25 mg/kg) produced hypotension, bradycardia and increased DA release in the striatum. On the other hand, amphetamine (0.5-1.25 mg/kg) produced hypertension, tachycardia and increased striatal DA release. However, intravenous injection of apomorphine (0.5-1.25 mg/kg) produced hypotension, bradycardia and decreased striatal DA release. In addition, the THP-induced hypotension was attenuated by pretreatment with spinal transection or amphetamine, while the THP-induced bradycardia was attenuated by pretreatment with bilateral vagotomy or amphetamine. Thus, it appears that THP acts through DA D-2 receptor antagonism to induce hypotension and bradycardia in rats.