Assessment of hamster blastocysts derived from eight-cell embryos cultured in hamster embryo culture medium-2 (HECM-2): Cell numbers and viability following embryo transfer

Abstract

The viability of hamster blastocysts, cultured from the eight-cell stage using hamster embryo culture medium-2, was examined by embryo transfer. Approximately 15–20 cultured hamster blastocysts were surgically transferred unilaterally to uterine horns of pseudopregnant recipient hamsters that had been mated to vasectomized males 3 days previously. Control recipients received in vivo developed, freshly recovered eight-cell embryos or blastocysts on day 2 or 3 of pseudopregnancy, respectively. Of the successful embryo transfers, the experimental group (receiving cultured blastocysts;n=10) gave 51.8% implantations and 28.2% live pups. These values were closely similar to those of the controls; the percentages of control implantations and offspring were 51.1 and 34.0%, respectively, for eight-cell embryo transfer (n=7,P>0.69) and 48.5 and 28.9% for blastocyst transfer (n=6,P>0.52). To evaluate the quality of cultured hamster blastocysts, the following two parameters were examined. (1) The mean number of cells per blastocysts was 24.4±0.7 for cultured blastocysts. This value was similar to that (range, 14–24) obtained in this laboratory for in vivo developed freshly recovered blastocysts. (2) Oxygen consumption analysis revealed that cultured blastocysts actively respired at a level close to that observed with freshly recovered eight-cell embryos (slopes of oxygrams: 0.25 and 0.26, respectively). From these results, it is concluded that hamster blastocysts, cultured from the eight-cell stage, are (a) qualitatively similar to freshly recovered in vivo developed blastocysts and (b) biologically viable as revealed by the production of live offspring upon embryo transfer. Therefore, hamster embryo culture medium-2 could be useful for studies relating to embryo-derived proteins involved in the process of implantation and for the production of transgenic hamster embryos, for example, using embryonic stem cells.