Cardiac effects of lappaconitine and N-deacetyllappaconitine, two diterpenoid alkaloids from plants of the Aconitum and Delphinium species.

Aconitum and Delphinium alkaloids are currently under investigation in search for new analgesic and anti-inflammatory drugs. It has been reported that the analgesic compound lappaconitine (LA), a C19 diterpenoid alkaloid from Aconitum sinomontanum nakai is an inhibitor of tetrodotoxin-sensitive, voltage-dependent sodium channels. In the present study we investigated the cardiac effects of LA and its metabolite N-deacetyllappaconitine (DLA) in electrically stimulated left and spontaneously beating right atria isolated from guinea-pig hearts. In all experiments, equieffective concentrations were larger with DLA than with LA. At a stimulation frequency of 2.5 Hz the time constant for the onset of LA effects (tau = 56 +/- 29 min) was markedly larger than the one for DLA effects (tau = 14 +/- 8 min). The compounds exerted a significant negative inotropic action at 0.06 microM (LA) and 0.2 microM (DLA). Asystolia of right atria occurred at 4.5 microM (LA) and 10 microM (DLA). Therefore, cardiotoxicity of LA and DLA was much lower compared to aconitine, which caused arrhythmia at 10 nM in our model. For both alkaloids a use-dependent mode of action could be demonstrated. In addition, preincubation with 0.3 microM LA prevented arrhythmia induced by aconitine or ouabain. We conclude that lappaconitine is a naturally occurring compound with class-I antiarrhythmic action.