Pharmacological Properties of β-Amyrin Palmitate, a Novel Centrally Acting Compound, Isolated from Lobelia inflata Leaves

Abstract

Abstract Effects of β-amyrin palmitate isolated from the leaves of Lobelia inflata were studied on the central nervous system of mice and were compared with those of antidepressant drugs, mianserin and imipramine. In the forced swimming test, β-amyrin palmitate, like mianserin and imipramine, reduced the duration of immobility of mice significantly in a dose-dependent manner (5, 10 and 20 mg kg−1). β-Amyrin palmitate (5, 10 and 20 mg kg−1) or mianserin (5, 10 and 20 mg kg−1) elicited a dose-related reduction in locomotor activity of mice and antagonized locomotor stimulation induced by methamphetamine. In contrast, imipramine (5, 10 and 20 mg kg−1) increased locomotor activity and potentiated methamphet-amine-induced hyperactivity. β-Amyrin palmitate showed no effect on reserpine-induced hypothermia, whilst mianserin (10 mg kg−1) and imipramine (10 and 20 mg kg−1) antagonized the reserpine-induced effect. Unlike imipramine, β-amyrin palmitate and mianserin did not affect haloperidol-induced catalepsy, tetrabenazine-induced ptosis and apomorphine-induced stereotypy. β-Amyrin palmitate and imipramine had no effects on the head-twitch response induced by 5-hydroxytryptophan, whereas mianserin (5, 10 and 20 mg kg−1) decreased it in a dose-dependent manner. A potentiating effect of β-amyrin palmitate (5, 10 and 20 mg kg−1) on narcosis induced by sodium pentobarbitone was stronger than that of imipramine (10, 20 and 40 mg kg−1) but weaker than that of mianserin (2·5, 5 and 10 mg kg−1). These results suggest that β-amyrin palmitate has similar properties in some respects to mianserin and might possess a sedative action. We suggest that β-amyrin palmitate has antidepressant activity with a mianserin-like profile of action.