Stimulation of LH release from cultured pituitary cells by saponins of Petersianthus macrocarpus: a permeabilizing effect.

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 micrograms/ml to 300 micrograms/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 micrograms/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 (greater than 30 micrograms/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.

Inhibitory effects of saponins from Tetrapleura tetraptera on the LH released by cultured rat pituitary cells.

Ethanolic extracts from stem bark of Tetrapleura tetraptera exerted an inhibitory effect on the luteinizing hormone (LH) released by cultured rat pituitary cells. These extracts contained triterpenic saponins, tannins, and flavonoids as estimated through phytochemical screening. Saponins were extracted. They apparently inhibited the luteinizing hormone-releasing hormone (LHRH)-induced LH release, the inhibition level being dose-dependent. Yet, the intracellular LH content remained constant whatever the saponin concentration, which demonstrated a lack of effect on the true release process. Accordingly, an interaction between saponins and LH released into the medium was demonstrated, which led to a decrease in the amount of immunoassayable hormone. This decrease was both time- and dose-dependent. It occurred even in the presence of serum in the medium, which suggests that the inactivation process may occur in vivo. Taken together, these results could explain the anti-gonadotrope properties of T. tetraptera extracts that are used as natural contraceptives in Ivory Coast pharmacopoeia.

Combretodendron Africanum bark extract as an antifertility agent. I: Estrogenic effects in vivo and LH release by cultured gonadotrope cells.

An aqueous extract from the stem bark of Combretodendron africanum was prepared to investigate its potency as a regulator of fertility. The intraperitoneal LD50 in mice was 95.2 +/- 4.3 mg/kg. Daily i.p. injections of 50 mg/kg promoted a significant increase in the uterine weight of 25 day-old female rats while pituitary weight remained unaffected. Similar injections for 21 days to mature females blocked the estrous cycle in the luteal phase with a mean length of efficiency of 15 days and decreased plasma LH and FSH levels. Regular cycles were restored 10 days following the last injection. C. africanum extract was shown to compete with estradiol and with progesterone on uterine receptors. Consequently, it is thought to contain substances exhibiting estrogenic (and possibly anti-estrogenic) potency. The effects of the extract on LHRH-induced release were investigated on cultured pituitary cells. Although gonadotropin release was amplified, the extract itself appeared as to be a potent secretagogue not requiring LHRH receptors. It follows that the active molecules contained in C. africanum extracts may be different from classical steroid estrogens.

[Natural substances regulating fertility. Effect of plant extracts in the Ivory Coast pharmacopoeia on the release of LH by hypophyseal cells in culture]. / Substances naturelles régulatrices de la fécondité. Action d'extraits de plantes issues de la pharmacopée ivoirienne sur la libération de LH par des cellules hypophysaires en culture.

The in vitro action of hydro-alcoholic extracts of plants from Ivory Coast pharmacopoeia was analyzed on cultured rat pituitary cells. Cells were treated for 24 hours with various doses of extracts and then stimulated for 4 hours with 10(-8) M LHRH. Extracts from Afrormosia laxiflora, Cola nitida, Pterocarpus erinaceus and Tetrapleura tetraptera inhibit the LHRH-induced release of LH. On the contrary, extract from Combretodendron africanum stimulates the basal release of LH and this increase is added to the LHRH-induced release. Therefore, the natural substances contained in these plants may in vitro exert a regulation of the gonadotropin release.