Effect of osmotic stress on the developmental competence of germinal vesicle and metaphase II stage bovine cumulus oocyte complexes and its relevance to cryopreservation

Impact of anisosmotic conditions on structural and functional integrity of cumulus–oocyte complexes at the germinal vesicle stage in the domestic cat

“…Compared to similar studies conducted in the cow (Agca et al, 2000), we discovered that the cat COC at the GV stage had the capacity to withstand the inherent stressors associated with a wide range of anisosmotic conditions (from 200 to 750 mOsm) without affecting subsequent structural or functional integrity, including blastocyst formation in vitro and quality. These two tolerated extremes represented 70% and 300%, respectively, of the normal isotonic environment experienced by the cat oocyte.…”

“…When exposed to permeating cryoprotectant, an oocyte re-expands after an initial shrinking that lasts <5 min (Critser et al, 1997), which is probably too short to disrupt cumulus-oocyte communications. At the same time, sucrose as an agent for regulating osmolarity offers an advantage over sodium chloride because it promotes hydrogen bond formation with phospholipids, thereby stabilizing membranes (Stachecki et al, 1998;Agca et al, 2000;Fabbri et al, 2001). This also could explain the differences in osmotic tolerance between the cat and cow oocyte, since studies of the latter relied on sodium chloride to alter culture conditions (Agca et al, 2000).…”

“…At the same time, sucrose as an agent for regulating osmolarity offers an advantage over sodium chloride because it promotes hydrogen bond formation with phospholipids, thereby stabilizing membranes (Stachecki et al, 1998;Agca et al, 2000;Fabbri et al, 2001). This also could explain the differences in osmotic tolerance between the cat and cow oocyte, since studies of the latter relied on sodium chloride to alter culture conditions (Agca et al, 2000). An examination of the proportion of MII oocytes that were fertilized and the proportion of the latter that cleaved revealed no difference across the entire range of anisosmotic conditions.…”

“…Another important prerequisite to developing a practical freezing protocol is understanding oocyte tolerance to radical changes in osmolarity that occur during adding and removing cryoprotectant and exposing the gamete to low temperatures (Critser et al, 1997). The resulting changes in cell volume have been shown to have significant effects on oocyte developmental competence in the mouse (Litkouhi et al, 1997), human (Newton et al, 1999;Mullen et al, 2004), cow (Agca et al, 2000), and rhesus monkey (Songsasen et al, 2002). However, no information is available on the impact of osmotic stress on the immature cat oocyte.…”

Cryopreservation of bovine oocytes: Current status and recent developments

“…Oocytes at the GV stage are more sensitive to anisotonic stress than MII oocytes [30]. High concentrations of sodium are detrimental to mouse embryos during freezing [31].…”