Effects Of Postmortem Interval On Mouse Oocytes And Embryos

Most oocytes used in all kinds of experiments were from animals killed in abattoirs. The body will take place physiological and biochemical changes,the impact on oocytes quality is in need of study. we studied the effect of the length of time the ovaries, oviducts and uterus remained in the mice after cervical dislocation on ovary oocytes, ovulation oocytes, zygotes and other stage preimplantation embryos. This study provided scientific proof to make better use of oocytes and embryos, as well as to effectively conserve organs. We obtained the results as follows: 1.With the time the oviducts remained in the body after the mice were killed extending, ovulation oocytes death rate and spontaneous activation rised. At the same time, with the increase of the oocytes age oocytes death rate and spontaneous activation rose too. 2.Among three groups, one was that oviducts were layed in M2, another one was that oviducts were obtained after delay while abdomen was opened wholly, the third one was that oviducts were obtained after delay while abdomen was opened half. Except the third group delayed for 15minute with the death rate of 27.8%, others had low death rate and the difference is not significant. Among three groups spontaneous activation rose in turn. In the first group no oocyte died or took place spontaneous activation. 3. Different strains have different reaction to the delay of oviducts in body after animal death. After 10min delay C57BL/6 mouse oocytes have death rate of 56.5%,significantely higher than Kunming mouse (47.6%);Spontaneous activation rates were respectively 13.3% and 46.0%, C57BL/6 were obviously lower than Kunming mouse.4. The oviducts were obtained after being delayed 5min 24h after the mice were injected with hCG. The oocytes were cultured in CZB. About 81.1% occurred spontaneous activation, evidently lower than parthenogenetic rate (96.4%) with SrCl₂. Spontaneous activable oocytes had high cleavage rate(93.2%) and 4-cell rate(87.3%). However, spontaneous activable oocytes had blastula development rate(18.7%) as low as parthenogenetic oocytes by SrCl₂(22.9%). 18 hours after the mice wereinjected hCG, oocytes were parthenogenetic activated about 64.6%, significantely higher than spontaneous and induced activation rate of 24h aged oocyte.5.20min delay didn't bring the pronucleus, 2-cell embryos, morula and blastula into death. After lOmin delay only 81.2% pronucleus developed to blastula, significantly lower than control (93.2%). 20min delay reduced the blastula development rate to 67.5% more lower than lOmin delay.6.After 30min delay cumulus-oocytes complexions were cultured in vitro, the mature rate was 97.2%, not different significantly compared to the control(98.5%).The treated group activated oocytes had 15.7% blastula development rate, not different significantly compared to the control (16.7%). Conclusion: 1. Short time delay don't result in ovary oocyte degeneration, but can interfere severely in ovulation oocytes, leading to death and spontaneous activation .With the aging of the oocytes in vivo, the effect gets more obvious. 2.Short time delay don't result in preimplantation embryos death, but impacted blastula rate of pronucleus embryos. 3.The postmortem delay of the oviducts in the mouse body made different effect on different strains mice. 4.0penning the abdomen reduced the effect of the delay on the ovulation oocytes. 5.Oocytes obtained after the oviducts were delayed in dead animal body for a short while 24h after the mice were injected hCG took place spontaneous activation and developed to blastula, but the blastula rate was very low because of the aging of the oocytes.