Relation between brain and reproductive organs and activity of nitric oxide during estrus cycle

Nitric oxide (NO) is a biological messenger and has various biological actions. NO is involved in all the ovarian functions; steroidogenesis, follicular development, follicule rupture, ovulation, regulation of corpus luteum functions and atresia of corpus luteum. NO plays a crucial role as a modulator of uterus smooth muscle contractility, regulation of menstruation, facilitate implantation and prevent dismenore. The expression of nitric oxide synthase (NOS) is regulated by gonadal hormones and gonadal hormones regulated by NOS expression. In this study, we investigated the relation between reproductive organs and brain and activity of NO during estrus cycle. 32 female rats were seperated by vaginal smear into four phases of estrus cycle (proestrus, estrus, metestrus, diestrus) and sacrified. Then, plasma, brain, uterus and ovaries were taken. For detemining the NO concentration, its stable end product nitrite and nitrate measured by the colorimetric assay. Plasma estradiol, LH and FSH levels analyzed by ELISA. In this study, there is significant difference among the different tissue NO levels at different phases of estrus cycle. Brain NO level was sigificantly high in metestrus, when uterus NO level was high in estrus phase. The NO levels of plasma and ovaries high in estrus, but the difference was not statisticaly significant.In conclusion, plasma, reproductive organs and brain NO levels are changing during estrus cycle. This differences indicate that physiological roles of NO on menstrual cycle and pathophysiology of diseases which is most common in women.Key Words: Estrus, Nitric Oxide, Rat, Reproduction.