Aspectos relacionados à ocorrência da polispermia durante a fertilização in vitro (fiv) em suínos

Abstract

Polyspermy is the most common pathological condition observed during the fertilization of oocytes and, in pigs its present greatest incidence, both in vivo and in vitro. In vitro fertilization is a technique that allows the study of the mechanisms by which the oocytes to block polyspermy, a fact of great importance, since in pigs, their occurrence exceeds 50% of oocytes penetrated. In vitro, the polyspermy occur due to several factors, and among those, are indicated, the fertilization of immature and/or aged oocytes, the high sperm capacitated concentration used, the failures in the process of reaction of the zona pellucida after the sperm penetration and failures in the release of cortical granules. Furthermore, in vitro studies have evaluated the role of cells and secretion of the oviduct and also the preovulatory follicular fluid in blocking the polyspermy in pigs. The addition of numerous molecules to the culture media in attempt to decrease the high rates of polyspermic penetration during the technique have also be performed. Other factors of high importance in the polyspermic penetration rates are the pH control and the calcium levels in the media used, the use of elevated temperatures during the fertilization and also the stay of high concentrations of potassium ions, very important for a appropriate hypermotility process, capacitation and acrosome reaction. Thus, suboptimal conditions in these characteristics also induce an increase in polyspermic fertilization rates. Therefore, the main problem of the in vitro fertilization is the high incidence of polyspermy and consequently low rates of embryonic development. Because of this, the pig is one species of choice for studying the mechanisms that involve the polyspermy, including in other species.