Studies on antidepressant and antinociceptive effects of ethyl acetate extract from Piper laetispicum and structure-activity relationship of its amide alkaloids.

Piper laetispicum C.DC. (Piperaceae), is an endemic climbing, glabrous plant distributed in the southern part of China. A novel alkaloid amide, Laetispicine, from it has been proven to possess antidepressant activity. In this present study, antidepressant and antinociceptive effects of the ethyl acetate extract (EAE) of P. laetispicum have been studied in forced swimming, open field, acetic acid writhing and formalin tests in KM mice. A significantly antidepressant-like effect was showing at doses of higher than 60 mg/kg, which was not due to an increase in locomotive activity. The EAE also presented an analgesic effect, in our studies. At lower doses (30 mg/kg) the antinociceptive effect was likely mediated via peripheral inflammation and changes in central processing, and at higher doses (120 mg/kg) that was due to both central and peripheral pathways. We also quantitatively analyzed the major components of EAE by HPLC and approached the structure-activity relationship between structure of amide alkaloids and its antidepressant activities. The antidepressant effective components of EAE might be Leatispiamide A and Laetispicine. In their molecular structures, the isolated double bond from benzene ring and conjugated double bond located at 2-3 and 4-5 were necessary for its antidepressant activity.