Quantitative aspects of protein synthesis in non-cultured and cultured rabbit blastocysts.

Day 4 rabbit blastocysts were cultured in Ham's F-10 medium supplemented either with homologous serum or uterine flushings. Development was assessed by leucine and methionine incorporation at 24 h and 48 h, respectively, after initiation of culture and compared with day 4 and day 5 non-cultured controls. After 24 h in culture, incorporation data were similar for both media groups. After 48 h, a significantly higher protein synthesis activity was found in blastocysts which had access to uterine secretions in vitro. However, incorporation levels of day 5 controls were not reached. Modes of incorporation of leucine and methionine revealed to be very similar in all experimental groups but ranged on a different level. Leucine was incorporated on a 5.5-fold higher level than methionine. We conclude that (i) supplementation of culture media with uterine secretions is beneficial for blastocyst development, and (ii) further studies should focus on non-serum components within the uterine fluid and their significance for embryonic development.