Effect of gonadotropins during in vitro maturation of feline oocytes on oocyte-cumulus cells functional coupling and intracellular concentration of glutathione

Information about the mechanisms of meiotic arrest and resumption of meiosis in feline oocytes is still limited. The aim of this study was to investigate the effect of the presence of gonadotropins during IVM, on meiotic progression in relation to the status of gap junction mediated communications between oocyte and cumulus cells, to the cAMP intracellular content, and to the intra-oocyte concentration of glutathione (GSH) in feline oocytes. Our results indicated that about 50% of cumulus-oocyte complexes (COCs) showed functionally open communications at the time of collection, while the remainder were partially or totally closed. After 3h of culture, the percentage of COCs with functional gap junctions was significantly greater in the group matured in the presence of gonadotropins than in those matured without them, where an interruption of communications was observed. Moreover, this precocious uncoupling was associated with a moderate increase of cAMP concentration in the oocyte, lower than in the group exposed to gonadotropins. Intra-oocyte glutathione levels decreased significantly after 24h of IVM, whether gonadotropins were present or absent during the culturing process. The presence of thiol compounds in the IVM medium induced an intra-oocyte GSH concentration significantly higher than that found in oocytes cultured without these compounds, and similar to the GSH content of immature oocytes. Moreover, the intracellular GSH concentration increased as meiosis progressed. The present study suggests that in feline oocytes, gonadotropins affect the dynamic changes in communications between oocyte and cumulus cells during IVM. However, the intracellular concentration of GSH is not influenced by the gonadotropin stimulation. Moreover, the presence of gonadotropins and thiol compounds results in an increase of GSH levels along with meiotic progression of the oocytes.