Intraoocyte cAMP elevation induces Metaphase-I arrest in rat oocytes

Meiotic cell cycle progression from metaphase-I (M-I) to metaphase-II (M-II) is crucial since oocyte prepares to release first polar body (PB-I) and get converted into mature female gamete. Any disturbance or abnormality during this period could affect formation and extrusion of PB-I and thereby oocyte quality after ovulation. The adenosine 3’-5’-cyclic monophosphate (cAMP) is one of the major signal molecules that regulate the meiotic cell cycle in mammalian oocytes. However, its role during spontaneous exit from metaphase-I (M-I) remains obscure. Therefore, we aimed to find out whether the cell permeable analogue of cAMP that is dibutyryl cAMP could inhibit spontaneous exit from M-I in rat oocytes cultured in vitro . Female rates were exposed to 20 IU pregnant mare’s serum gonadotrophin (PMSG) for 48 hr followed by 20 IU hCG for 10 hr and then cumulus oocyte complexes (COCs) were collected from ovary by puncturing follicles with 26 gauze needles in pre-warmed M-199 culture media. The COCs were cultured in a fresh medium containing various concentrations of db-cAMP (0.0, 0.125, 0.25, 0.50 and 1.0 mM) for 5 hrs in vitro . Our data suggest that db-cAMP prevented oocytes from undergoing spontaneous meiotic resumption from M-I stage in a concentration-dependent manner. The 1.0 mM db-cAMP was sufficient to maintain cell cycle arrest at M-I stage during in vitro culturesuggest that 1.0 mM db-cAMP could be used to prevent spontaneous resumption as well as oocyte aging during in vitro handling of oocyte in various assisted reproductive technology (ART) programs.