by Chiu Tak Yu Tony. / "June 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (p. 156-182). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

No description available.

Acquisition of full developmental competence of oocytes not only occurs during growth stage, and the final preparation during oocyte maturation is also critical. Previous studies have shown that nuclear maturation can occur spontaneously following culture in vitro; however, there may be some insufficiency in cytoplasmic maturation of the in vitro matured oocytes. But till now, the differences of the events of cytoplasmic maturation between in vitro and in vivo matured oocytes are still not clear. Ovarian stimulation by gonadotrophins is used to permits the growth and development of follicles, to time the initiation of pre-ovulatory oocyte maturation, and to increase the numbers of oocytes ovulated. It is one of the foundations of current treatments of human infertility. The success of clinical IVF has been depending on generation of matured oocytes at high frequency. However, ovarian stimulation with gonadotropins is associated with side effects and complications. / In order to illuminate mechanisms which affect the developmental competence of oocytes produced in vitro, in the present study, we have compared the difference of the quality of oocytes produced in vitro with that of the oocytes produced in vivo using mouse model. In order to understand the relationship between oocyte competence and ovarian responses to stimulation in the mouse, we also have compared difference of the quality of oocytes produced in vitro or in vivo from gonadotrophns stimulated ovaries with that of from natural cycling ovaries. / In-vitro matured oocytes were collected from (1) naturally ovulated mice and (2) superovulated (PMSG + hCG) mice. Immature oocytes were retrieved from (3) naturally cycling mice, and (4) from mice primed with PMSG. The results indicate that the percentages of cleavage and blastocyst formation are significantly different (P<0.05) between in-vivo and in-vitro matured oocytes. Blastocyst formation rate is significantly higher (P<0.05) in immature oocytes derived from PMSG primed mice compared to immature oocytes derived from naturally cycling mice. The percentages of oocytes with comet tails and the length of comet tails are significantly higher and longer respectively in in-vitro matured oocytes compared to in-vivo matured oocytes. Total cell numbers of blastocyst are also significantly different (P<0.05) between in-vivo and in-vitro matured oocytes. However, there are no differences in ratio of trophectoderm (TE)/inner cell mass (ICM) between in-vivo and in-vitro matured oocytes. In conclusion, in-vivo matured mouse oocytes are more competent than those of matured in-vitro, suggesting that it may be due to its less damage of DNA. Embryonic development capacity of in-vivo matured oocytes is not promoted by ovarian stimulation. Gonadotropin priming prior to immature mouse oocyte retrieval is beneficial to subsequent embryonic development. / Keywords. mouse oocyte, IVM, IVF, gonadotropin, development

A delicate balance of steroid and gonadotrophic hormones is essential for intrafollicular oocyte maturation and successful fertilization and embryonic development. Previous studies have demonstrated that a superovulatory dose of pregnant mare serum gonadotrophin (PMSG) has excessive gonadotrophic activity and alters intrafol1icular steroid hormone levels. In a series of four experiments, the morphology of oocytes and embryos retrieved from immature rats, treated with either a low or high dose of PMSG, and mature, cycling rats was compared to determine whether a superovulatory dose of PMSG has an adverse effect on oocyte maturation and subsequent fertilization and embryonic development in immature rats. Morphological criteria for the assessment of intraoviductal oocyte aging were established in the first experiment. During intraoviductal aging, progressive morphological changes directed by the intrinsic developmental program of the oocyte were observed. Further alterations in morphology were attributed to abnormalities of cytoskeletal function. In the second experiment, no difference in morphology was observed between oocytes retrieved from immature rats treated with either 4 or 40 IU PMSG. When compared with mature rats, changes attributable to cytoskeletal instability were observed in aged oocytes from immature rats treated with both doses of PMSG. This was concluded to be a manifestation of altered intrafollicular oocyte maturation as a result of the administration of exogenous gonadotrophin. In the third and fourth experiments, delayed fertilization and a significant reduction in fertilization rate were observed in superovulated, immature rats. The major cause of fertilization failure was determined to be intraoviductal oocyte aging. A significant increase in abnormal embryos was observed as a result of parthenogenetic activation of the aged oocytes. Abnormal, fertilized embryos retrieved from the superovulated group were concluded to be the manifestation of delayed fertilization. In conclusion, the major effect of a superovulatory dose of PMSG on oocyte fertilizability and embryonic development was intraoviductal oocyte aging and delayed fertilization. Changes attributed to altered intrafol1icular maturation were manifested during oocyte aging in immature rats treated with either the low or high dose of PMSG. / Medicine, Faculty of / Obstetrics and Gynaecology, Department of / Graduate