TETRAHYDROPALMATINE, (+)- is an alkaloid found in the plants of the Carydalis species. Tetrahydropalmatine (THP) has two enantiomers with different effects on the brain dopaminergic system. Dopamine (DA) content reduction in the rat striatum induced by d-THP is much more dose-dependent. At a small dose, d-THP predominantly reduced the DA level but left serotonin and noradrenaline level unaffected. d-THP is probably a DA depletor. There were stereoselective differences between the two THP enantiomers on the activity of cytochrome P450 (CYP450) isozymes, i.e., d-THP had the potential to inhibit the activities of CYP2D6 and CYP1A2 isozymes, while l-THP inhibited CYP1A2 isozyme and induced CYP3A4 and CYP2C9 isozymes. The plasma levels of l-THP were always higher than those of d-THP in rats.

Protopine is the isoquinoline alkaloid found primarily in the plant families Berberidaceae, Ranunculaceae, Rutaceae, Fumariaceae. It has diverse biological activities, such as anti-thrombotic, anti-inflammatory, anti-parasitic activity, antimicrobial activity, as well as hepatoprotective effects in animal models. The biological activities of protopine are associated with its ability selectively inhibits K(ATP) channels by targeting on SUR1 subunit. In addition, was discovered that β2 -adrenoceptor (β2 -AR) is a target for antiasthma activities of protopine. On this target, binding of the drug occurs on the amino acid residual of Ser 169 through the formation of hydrogen bonds and receptor‐drug bumps.