Stimulation of LH Release from Cultured Pituitary Cells by Saponins of Petersianthus macrocarpus: A Permeabilizing Effect

Abstract

Aqueous extracts from stem bark of Petersianthus macrocarpus contain substances exhibiting both estrogenic and antiestrogenic potency. Triterpenic saponins were identified and extracted as a bulk. Their action on the in vitro LH released by cultured rat pituitary cells was investigated. P. macrocarpus saponins stimulated the LH release in a dose-dependent manner (from 10 µg/ml to 300 µg/ml). When added simultaneously, saponins and LHRH exerted initial additive effects on LH release, demonstrating independent mechanisms of stimulation. If cells were pre-treated with saponins for 15 min, the amount of LH released under a subsequent LHRH stimulation was lowered, presumably due to a partial depletion of the cells in hormone (data not presented). However, the action of saponins on LH release did not appear specific since a general permeabilizing effect of the cell membrane was evidenced both by trypan blue exclusion and by analysis of the total protein output. When using low concentrations of saponins (10 µg/ml), scanning electron microscopy did not reveal any significant alteration of the cell structure, which explains why the cells remain responsive to LHRH after withdrawal of saponins. With higher concentrations (> 30 µg/ml), the same analytical studies evidenced numerous perforations of the cell membrane, with subsequent cell death. Two highly purified saponin species were tested on LH release by cultured cells; one of them (petersaponin I) appeared responsible for the observed biological effects in vitro. But as cells were shown to be efficiently protected from saponin effects by the presence of serum, it may be concluded that saponins of P. macrocarpus extracts are probably not candidate molecules promoting the in vivo estrogenic and antiestrogenic effects.

Key words

Petersianthus macrocarpus - LH release - pituitary cells - saponins - petersaponin 1 - estrogenic activity - antiestrogenic activity - membrane permeabilizing effect