Studies of the physiology and biochemistry of early development in the preimplantation sheep embryo

Christine Lesley Cuneo

Preimplantation sheep embryos were collected during the initial period of embryogenesis by flushing the uteri of ewes in situ at 13, 15, 17 and 19 days after mating. The embryos and associated embryonic structures (trophoblast, yolk sac and allantois) present at each age were separated for further investigation. An initial study established the lyophylised weight of embryonic structures present at each stage of development. These values were used as a basis for later comparison of the metabolism of these structures. Changes in the pool sizes of the macromolecules, glycogen, protein, DNA and RNA with development were also determined. The major part of the project dealt with estimates of the anabolic metabolism, in particular the synthesis of glycogen, protein and RNA, by the different embryonic structures emerging over this period. Embryos and samples of the embryonic membranes were incubated in a variety of culture media containing radiolabelled precursors. After incubation, samples were recovered, lyophylised, weighed then fractionated to assess uptake and incorporation of precursors. The parameters measured were compared per unit dried weight or in terms of total incorporation per structure. Precursors used were U-14C-glucose, U-14C-amino acids and 5-3H-uridine. The results of these studies indicated that there is both a divergence in synthetic activity between structures and a change in synthetic rate of individual structures as development progresses. Finally a preliminary study of uterine fluid was undertaken. By analysis of fluid obtained by rinsing uteri in situ the volume of fluid in the uterus of the ewe at various times after ovulation was measured. The concentrations of cations and energy substrates in this fluid were estimated in order to gain some understanding of the environment for the embryo in vivo.

Studies of the physiology and biochemistry of early development in the preimplantation sheep embryo

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