Isolation and identification of tetrahydrocolumbamine as a dopamine receptor ligand from Polygala tenuifolia Willd

The isolation and purification of a dopamine receptor ligand, tetrahydrocolumbamine from Polygala tenuifolia Willd is described. Tetrahydrocolumbamine was shown to inhibit the binding of [3H]-SCH23390 and [3H]-spiroperidol to rat striatum membranes in vitro with IC50 values of 0.75 +/- 0.08 mumol.L-1 and 0.92 +/- 0.10 mumol.L-1, respectively. The compound inhibited the binding of [3H]-prazosin (IC50 value of 46 mumol.L-1), while it did not change the binding of the ligands, [3H]-QNB and [3H]-muscimol to rat cortex in vitro. Scatchard plot analysis showed a mixture of competitive and non-competitive inhibition by the compound on both [3H]-SCH23390 and [3H]-spiroperidol binding to membranes from rat striatum.