One‐cell hamster embryos placed in culture have always shown a complete block to development at the two‐cell stage. In a preliminary study using a chemically defined culture medium containing 20 amino acids (HECM‐1), many one‐cell embryos were able to escape the “two‐cell block” and develop to the four‐cell stage. Use of a simpler formulation containing only the amino acids hypotaurine and glutamine revealed marked inhibitory and stimulatory effects of adding the other amino acids. In the first experiment, 19 amino acids were separately examined for effects on one‐cell embryo development. Six amino acids (phenylalanine, valine, isoleucine, tyrosine, tryptophan, and arginine) inhibited embryo development (reduced mean cell number; MCN), and three others (glycine, cystine, and lysine) stimulated development (increased MCN), compared with basic medium containing only glutamine and hypotaurine (low control). When the responses with the six inhibitory amino acids were totalled, only 3 of 185 (2%) one‐cell embryos reached the six‐or seven‐cell stage compared to a total of 15 of 76 (20%) embryos that developed to these stages using the three stimulatory amino acids. When tested together in a second experiment, the six inhibitory amino acids significantly reduced the MCN, from 4.28 ± 0.44 (low control) to 3.71 ± 0.55. In this group, 17 of 117 (15%) of one‐cell embryos reached more than four‐cell and only 4 of 117 (3%) reached six‐ or 7‐cell stages, compared with 39 of 117 (33%) and 12 of 117 (10%), respectively, for the basal medium group. The stimulatory (glycine, cystine, lysine) and “neutral” (cysteine‐SH, proline, serine, threonine, histidine, alanine, hydroxyproline, leucine, aspartic acid, methionine) groups did not significantly alter the MCN, but both supported development of a substantial proportion of one‐cell embryos to more than four‐cell stages (38% and 48%, respectively, of 126 embryos in each group), and to six‐ or seven‐cell stages (20% and 29%, respectively, for the stimulatory and neutral groups). In these two groups, a few one‐cell embryos even reached the eight‐cell or blastocyst stages. This study shows that the type of amino acid in the culture medium has a profound influence on the number of cleavage divisions undergone by one‐cell hamster embryos and suggests that, at least in vitro, amino acids may play an important regulatory role in early preimplantation development in this species. Copyright © 1990 Wiley‐Liss, Inc.
