Senecio biafrae, which is the plant of interest in this study, is used by some people in Africa for its nutritional and pharmacological properties [6, 7, 9–11]. Its effect on the onset of puberty (age and phase of the estrous cycle at vaginal opening) and the ovarian folliculogenesis of immature female rats were evaluated. The choice of these parameters was not only guided by the influence of the gonadotrophic hormones (FSH, LH, PMSG, GnRH) on the precocious onset of puberty and the induction of the follicular growth in immature female rats, but also by the clinical usage of these hormones in the treatment of various forms of infertility (ovulatory defects or hypogonadal infertility) . Puberty is the culmination of a complete sequence of maturational events that lead to the activation of the gonadotrophic axis, linked to the increase in serum levels of LH and FSH and attainment of sexual maturity. Estradiol has been reported to peak just before the vaginal opening in female rats, showing that it is the effective molecule for puberty induction . In various mammals, precocious puberty onset can be induced in a prepubertal animal by repeated injections of GnRH, FSH, LH or of an analogous compound of a general excitatory neurotransmitter of the central nervous system, like glutamate or aspartate which induce the pulsatile releases of GnRH . The pulsatile secretion of GnRH hormone at puberty leads to the pulsatile release of FSH and LH. These pituitary hormones in turn enhance the proliferation of the follicular cells and the production of estrogens (principally estradiol) by ovarian cholesterol catabolism . The overall hormonal signalization culminates in the opening and cornification of the vagina, and to the increase in ovarian and uterine weight .
Oral administration of AESb for 30 days, at doses of 32 and 64 mg/kg, to immature female rats led to a precocious onset of vaginal opening. This shows that the plant extract could contain molecules acting, as one of the above compounds, on the precocious onset of puberty. The same result was obtained, at 8 mg/kg dose, with the ethanolic extract of the plant . This shows that the active compound of the plant would be more extracted by organic solvents.
The opening of the vagina on attainment of the pubertal age of rats resulted from the increase in the secretion of estrogens by ovarian follicles. The vaginal cells are also keratinized in this high estrogenic environment . That is why the vaginal smear of pubertal rats the day of vaginal opening corresponds to the estrus phase of the cycle or to the nearest phase following it (metoestrus), as shown in Table 1. In animals treated with 8 and 32 mg/kg doses, the proestrus phase (preovulatory phase) was slightly reduced. This could be linked to the acceleration in the ovarian follicular growth, given the high estrogenic environment of the ovarian cells, following the induction of pulsatile secretion of GnRH and gonadotrophins by AESb.
A significant reduction in the body weight gain of animals, after three weeks of oral administration of AESB, was also noticed. During the same period of treatment, no significant changes in various biochemical parameters of toxicity (data not shown) nor in the daily food intake of AESB treated animals was observed. Thus, this body weight reduction may be related to the cumulated slight decrease, during the same period of treatment, in food intake of those treated with the doses of 32 or 64 mg/kg of AESB.
Estrogens and estrogen-like compounds (phytoestrogens) are well known regulators of growth and differentiation in a number of tissues. They exert their biological effect following their fixation to the receptors in their main target organs (ovary, uterus, hypothalamus, bone,...) thus leading to a chain of reactions, culminating in the biosynthesis of biomacromolecules (DNA, RNA, and proteins) and the increase in the weight of these organs, principally the ovary and uterus [1, 40, 41]. This weight increase is a combination of hypertrophic response of tissues following cell proliferative activities and water imbibition in the tissue . The data on uterine parameters presented in this study has shown an increase of more than 96% and 87% in uterine proteins and uterine weight respectively, at all the doses. This increase in uterine proteins and weight may have resulted not only from the uterine cell proliferation induced by the oestrogenic effects of some chemical components of AESB but also from the increase in their water imbibition effect, especially at low dosage, in these cells. This estrogenic potential of AESB is also attested with the increase, at the dose of 8 mg/kg, in ovarian weight and corpora lutea number.
As concerns the test on gestational parameters, a slight reduction in the number of corpora lutea, and gestational rate with the highest dose (64 mg/kg) could be linked to the reduction in the ovulation rate of these animals following the negative feed-back effect, at the level of the hypothalamus, of high estrogen level induced by this dose of the extract . This could also results from the fact that estrogenic compounds cause contraction in the uterine smooth muscle, which could lead to the resorption of the fetus after its implantation .