Maintaining the normal vaginal fluid acidity

Maintaining the normal vaginal fluid acidity is important for vaginal functions (Wagner and Levin 1984). Estrogen has been shown essential in maintaining the acidity of vaginal fluid, in which its deficiency could cause vaginal fluid pH to increase (Gorodeski et al. 2005). After menopause, low estrogen levels have been found to increase the risk of vaginal and urinary tract infections (Raz and Stamm 1993). Thus, restoring the estrogen levels near normal either via exogenously administering estrogen or estrogen-like compounds are important to overcome complications related to low estrogen levels. We have shown that oral treatment with MPE ameliorates the increase in vaginal fluid pH in sex-steroid deficient state, and this suggested that MPE could be used to overcome the abnormal vaginal milieu in E deficient condition. In view of the effect of MPE was almost similar to E, there is a possibility that the compounds present in MPE might possess estrogen;like effects. Quercetin and kaempferol are the two known estrogen-like compounds (Palma-Duran et al. 2015) which could produce effects similar to estrogen. Besides, rutin (Horcajada‐Molteni et al. 2000) and myricetin (Aquila et al. 2013) which were also reported to possess estrogen-like activities might also be capable of producing the vaginal effects resembles that of estrogen. In this study, the mechanisms underlying the lesser increase in vaginal fluid pH following MPE and E treatments have been proposed. MPE and E were found to up-regulate the expression of V-ATPase A & B in the vagina. Furthermore, the findings from this study found that V-ATPase was expressed at the apical membrane of the vaginal epithelium, which suggest that this protein could be involved in H+ extrusion into the vaginal lumen. Our findings were similar to the reported apical distribution of V-ATPase in human cervical-vaginal epithelial Concanamycin A synthesis (hECE) (Gorodeski et al. 2005). In the meantime, our findings which indicate V-ATPase expression in the vagina was increased under the influence of E was consistent with a report that shows estrogen deprivation attenuates while estrogen treatment augments active H+ secretion into the vagina of post-menopausal women (Gorodeski 2005). Therefore, up-regulation of V-ATPase A and B by MPE could be the likely mechanisms that restore low vaginal fluid pH in sex-steroid deficient condition. The other mechanisms that might also contribute towards the lesser increase in vaginal fluid pH following E and MPE treatments are the up-regulation of CA isoenzymes i.e. CAII, CAIII, CAIX, CAXII and CAXIII, which are known to participate in H+ generation. To the best of our knowledge, this study is the first to show that the levels of CA isoenzymes in the vagina were increased under E influence. The importance of CA isoenzymes in general in luminal fluid acidification has been described. CAII plays important role in the conversion of CO2 and H2O to H2CO3, which then dissociates into H+ and HCO3− (Boron 2010). CAII has also been shown to interact with HCO−3 transporter including Cl−/HCO3− exchanger (Sowah and Casey 2011). These might affect the luminal fluid pH i.e. causing luminal fluid pH to decrease. CAXII, which is expressed at the apical membrane of the epithelium could participate in the conversion of H+ and HCO3− in the lumen into CO2 and H2O, where both diffuse back into the cell to ensure continuous H+ and HCO3 generation (Karim et al. 2016a). We have shown that in vagina, CAXII expression is under the influence of E. On the other hand, in the uterus, expression of this isoenzyme is under the influence of progesterone (Karim et al. 2016a). Besides CAII and CAXII, other CA isoenzymes including CAIII, IX and XIII which are also expressed in the vagina might also be involve in the acidification of vaginal fluid. Ability of MPE to up-regulate expression of these CA isoenzymes in the vagina suggested that H+ generation could be stimulated, leading to acidification of the vaginal fluid.