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Studies of the metabolism and viability of preimplantation mammalian embryos

Ryan, John Patrick (1990) Studies of the metabolism and viability of preimplantation mammalian embryos. PhD thesis, Murdoch University.

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Abstract

The studies reported in this thesis examine the effects of a number of variables on the production, metabolism and viability of mammalian embryos. Specifically, the studies assessed factors influencing the production of sheep embryos, the use of embryonic metabolism as an indicator of viability and the effects of platelet-activating factor (PAF), a phospholipid produced by embryos during early pregnancy, on embryonic metabolism and viability.

Variations in rates of embryo recovery, fertilisation and development, and the incidence of persistent large follicles and the regression of corpora lutea affected the production of viable sheep embryos following superovulation with PMSG and/or FSH. These variables in turn were influenced by dose of gonadotrophin, the administration of GnRH, nutritional status, lactational status and age of the donor, season, timing of ovulations, time of insemination and cryopreservation.

The production of 14CO2 from DL[l--14C] lactate by preimplantation mouse and sheep embryos was measured and evaluated as an indicator of developmental potential. For embryos of both species, a positive correlation between the oxidative metabolism of lactate and subsequent developmental potential was observed. The reduced viability of mouse embryos exposed to suboptimal culture conditions was also reflected in decreased rates of lactate oxidation. Furthermore, the influence of a number of factors on the metabolism of sheep embryos was assessed. These included cell stage, the use of semen from different sires, the collection of embryos from different ewes and cryopreservation of spermatozoa used for insemination.

Direct effects of platelet-activating factor (PAF) on the oxidative metabolism of glucose and lactate by preimplantation mouse, sheep and polyploid human embryos were demonstrated. Using lyso-PAF and a specific PAF-receptor antagonist, SRI 63-441, the specificity of the effect of PAF on mouse embryos was demonstrated. The effects of PAF on the activity of the pentose phosphate pathway and the incorporation and turnover of glucose carbon in various biochemical fractions of mouse embryos were also evaluated. In relation to this, PAF was shown to have marked effects on the acid-soluble glycogen fraction of mouse morulae and early blastocysts. Supplementation of culture medium with PAF increased cell numbers in blastocysts, cultured from the 2-cell stage, and their ability to oxidise lactate. Moreover, it significantly increased the ability of mouse embryos to implant following transfer to pseudopregnant recipients.

In conclusion, these studies have (i) identified a number of variables that influence the production of sheep embryos following superovulation, (ii) demonstrated a relationship between the oxidative metabolism of lactate by embryos and their viability and (iii) established that exogenous PAF has a direct effect on the metabolism and viability of embryos cultured in vitro suggesting an autocrine role for embryo-derived PAF in early pregnancy.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary Studies
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Wales, Ray
URI: http://researchrepository.murdoch.edu.au/id/eprint/53056
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