The use of natural substances as hormonal-replacement therapy in menopause is well documented in the literature though the availability and safety margin is a source of concern. In this study, germinated brown rice and its bioactives after eight weeks of oral treatment grossly restored the weight and length of atrophied uteri and vagina of rats compared to those of oophorectomised non-treated control group. A significant increase in both the weight and length of the uterus and the vagina was observed when comparing the sham-operated with the oophorectomised non-treated groups, and the groups treated with GBR, ASG, oryzanol, GABA and oestrogen with the group treated with Remifemin(p < 0.0001). Similar effects were observed on uterine weight between oophorectomised and non-oophorectomised rats treated with Daidzine, Genistein, oestradiol or honey [
32‐
34].There are observable differences on the vaginal cytology between the various treatment groups compared with the oophorectomised non-treated rats, including the ratio of distribution between the three cells. Cornified cell were observed in high number in the group treated with GABA fractions, the epithelial cells were observed in higher number in groups treated with oestrogen, oryzanol and ASG, while the group treated with GBR had almost an equal number of the two cells. Oestrous cycle is a rhythmic reproductive cycle that is influenced by the release of gonadotropin-releasing hormone from the hypothalamus, gonadotropins from the pituitary gland and sex hormones from the gonads [
35]. The average number of vaginal cells at a particular time of the oestrous cycle gives a clear picture of the functional status of the neuro-endocrine – reproductive system and ovarian activity [
36]. Therefore, the high number of cornified as well as epithelial cells observed after treating the rats with GBR and its bioactives indicate the effects of these compounds in restoring the neuro-endocrine reproductive and ovarian function already lost due to oophorectomy. These changes observed on vaginal cytology and gross modification may be an indication that GBR and its bioactives possess oestrogenic activity, and Remifemin has little or no effect on the uterine tissue as earlier reported [
37]. Histologically, rat uteri treated with GBR and its bioactives showed increased activity of the uterine cells and also the glands. PCNA, which is an indicator of DNA synthesis as well as cell proliferation, showed positive reactions on the treated cells and this showed that the cells are on their early propagation and duplication at the synthetic (S) phase cycle as reported by other workers [
38,
39]. Thus, the cells of the treated groups were in the early stages of duplication and showed strongly positive nuclear reactivity. The PCNA reaction also correlated well with the stages of oestrous cycle in this study and this finding is comparable with an earlier study [
21]. It has been reported that mitosis usually increased from dioestrus toward proestrus, while cell death and apoptosis was low at this stage, and high towards oestrous, and the observation is related to the concentration of ovarian steroid hormones that increases at dioestrus and proestrous and decreases towards oestrous [
40,
41]. In this study, we observed that our sham- and oophorectomy-treated rats hada higher average number of cornified and epithelial cells than the oophorectomised non-treated groups, which showed that the GBR- and its bioactive compound-treated oophorectomised rats were mostly at their pro- or dioestrous stage of the oestrous cycle. A positive light-brown staining immunoreactivity was observed in the control sham groupand ASG- and oryzanol-treated groups at both the stroma, glandular and luminal epithelium –this clearly indicated that the induction of proliferation by these compounds was controlled and minimal. Previous studies have shown that GBR contains a lot of bioactives that have antioxidant [
26,
42], anti-colon cancer [
43], anti-diabetic [
29,
44‐
46] and other numerous effects, ASG, for instance, which is a glycosidase, has been implicated in physiologically important processes in plants, such as response to biotic and abiotic stresses, defence against herbivores, activation of phytohormones, lignification and cell-wall remodelling [
47]. Despite the fact that the different compounds give almost the same gross effects in terms of restoring the measured anatomical indices of the uterus, cytological evidences showed variability in distribution of leucocytes and epithelial and cornified cells across the treatment groups(Table
2). Likewise, the histological appearance of the various cells in the groups showed different configurations in term of glands, epithelial lining and activity (Figure
2). Furthermore, the PCNA reaction observed within the various treatment groups varied in the staining pattern of the cells. These differences may be as a result of different molecular mechanisms of action, which need to be ascertained in further studies.