It has previously been shown that high osmolarity is detrimental to cleavage-stage mouse embryo development in vitro, and that the presence of several organic osmolytes can provide protection against the detrimental effects of raised osmolarity. Whether the same is true for post-compaction stage embryos is unknown. In the present work, it was found that mouse post-compaction stage embryo development was inhibited by raised osmolarity. However, inhibition of embryo development from the 8-cell to

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... the blastocyst stage occurred only at much higher osmolarities than that which inhibited development from the 1-cell stage. Glutamine, glycine, L-alanine and beta-alanine, which have been proven to function as organic osmolytes providing protection against increased osmolarity in cleavage-stage embryos (during the 1-cell through 4-cell stages), also protected post-compaction stage embryos from the detrimental effects of high osmolarity. Two other organic osmolytes, betaine and proline, which are effective in pre-compaction embryos, were not effective in providing protection against raised osmolarity in embryos developing in vitro from the 8-cell stage, nor were myo-inositol and taurine, which have been shown to be ineffective in cleavage-stage embryos. In addition, cleavage-stage embryos and post-compaction stage embryos were found to use different transport mechanisms to accumulate the four organic osmolytes that provided them with osmoprotection. When assessed in morulae, the amino acid transport system beta was found to be responsible for beta-alanine transport, while transport system B0+ mediated transport of glutamine, glycine and L-alanine. Glutamine, glycine, L-alanine and beta-alanine supported post-compaction stage embryo development, higher embryo cell number in blastocysts, and greater embryo volume at higher osmolarities. The four compounds identified do not share metabolic pathways or other such properties in common, and thus it is likely that post-compaction mouse embryos utilize them, in large part, as organ [...]