Thunbergia laurifolia Linn. (TH) and Simplocos racemosa Roxb. (SY) are herbal medicines used in the treatment of drug addiction without scientific support for their mechanism of action. The present study investigated the effects of these medicinal plants on dopaminergic neurotransmission in comparison with amphetamine. The effect of crude water extracts (0.1 g/ml) of TH and SY on K(+) (20 mM)-stimulated dopamine release from rat striatal slices were compared with amphetamine (10(-4) M) using high-performance liquid chromatography with electrochemical detection to measure endogenous dopamine. Amphetamine and TH, but not SY, significantly increased K(+)-stimulated dopamine release (P < 0.001) from rat striatal slices when compared with K(+)-stimulated alone. TH potentiated the effect of amphetamine on K(+)-stimulated dopamine release (P < 0.001) when compared with amphetamine alone. The results indicate that TH may stimulate dopamine release in the same manner as amphetamine. It remains to be determined whether the effect of these extracts on dopamine function is important in their therapeutic use in the treatment of drug addiction.
Copyright 2002 Elsevier Science Ireland Ltd.