Comparative analysis of in vitro development of outbred mouse embryos cultured in Krebs-Ringer or tyrode-derived media.

Culture media for mouse preimplantation development are usually derived from two basic solutions: Krebs-Ringer and Tyrode. We have used outbred mice (OF1) to make a comparative analysis of derived media of both types and their success in sustaining development from the one-cell to the blastocyst stage. The best results (up to 50%), in terms of overcoming the two-cell block and sustaining development to expanded blastocyst, were obtained with media derived from Tyrode's solution and with Krebs-Ringer-based media in which the high concentrations of certain metabolites (Cl-, K+, Mg2+ and PO(4)3+) were reduced to the values present in the Tyrode-derived media. Interestingly, medium T6 (based on Tyrode and incapable of avoiding developmental block on its own), yielded the best development rate with the addition of ethylenediaminetetraacetic acid (EDTA). The addition of glutamine to medium T6 did not have any effect. We further developed T7, a medium based on T6 but incorporating the concentrations of nutrients present in the oviduct. This medium also proved better than its Krebs-Ringer counterpart (MTF), but not better than T6, probably due to the different nutritive requirements in the transition from morula to blastocyst. The two most significant findings were: i) that Tyrode-based formulations were superior to media based on Krebs-Ringer solution, and ii) that medium T6 with EDTA was as effective for mouse egg culture as the recently developed KSOM medium.