[Oxidation and female reproduction: the good, the bad and what's between]

Reactive oxygen and nitrogen species constitute an inseparable part of aerobic life on earth. They have been known to science for about 90 years, but only during the last 50 years research in this field has expanded. Initially, scientists focused on the free radicals-induced damage to biological systems. Since the eighties, a new concept has emerged, namely, that alongside the oxidative stress-induced deleterious effect and its association with a variety of diseases, a certain threshold level of oxidation is essential to intracellular signaL transduction. Recently, some data has accumulated regarding the involvement of oxidative processes in various aspects of female reproduction, including ovarian function, fertilization, early development of the embryo and implantation. Nevertheless, there is still a long way before comprehensive and thorough understanding of their role, both at the molecular level and the expression in the clinical setup of fertility patients can be achieved. In this article, we shall address some molecular biochemical processes involved in the activity of free radicals, and review the present knowledge regarding their role in female fertility, including ovarian physiology, follicular and oocyte maturation, development of the early embryo and implantation, as well as their association with reproductive pathologies such as endometriosis, polycystic ovary disease and recurrent pregnancy loss.