DIFFERENCES IN AMINO-ACID CONTENT OF PREIMPLANTATION MOUSE EMBRYOS THAT DEVELOP IN-VITRO VERSUS IN-VIVO - IN-VITRO EFFECTS OF 5 AMINO-ACIDSTHAT ARE ABUNDANT IN OVIDUCTAL SECRETIONS

Although it is now well established that amino acids can improve preim plantation development of mouse embryos in vitro, the mechanisms by wh ich they influence development have not been determined. To investigat e these mechanisms, we compared the contents of seven abundant amino a cids (alanine, aspartate, glutamate, glutamine, glycine, serine, and t aurine) in 4-8-cell embryos and blastocysts developing in vivo with th e contents in those developing from the 2-cell stage in vitro. We also studied the effects of five amino acids (alanine, glutamate, glutamin e, glycine, and taurine) that are abundant in the oviductal lumen on t he amino acid content of embryos developing in vitro. Blastocysts that developed in vitro contained about six times more alanine and about o ne-sixth as much taurine as blastocysts that developed in vivo, but th ey contained about the same amounts of glycine and serine. In the pres ence of glycine and four other abundant amino acids in oviductal secre tions, however, blastocysts that developed in vitro had higher levels of both glycine and serine than those that developed in vivo. In contr ast, glycine either alone or in combination with the other amino acids reduced the alanine content of blastocysts developing in vitro to nea rer that of blastocysts developing in vivo. Similarly, taurine in the medium allowed blastocysts developed in vitro to increase their conten t of this amino acid to normal levels. The levels of taurine and, some what surprisingly, glutamine and glycine became abnormally low in embr yos within 24 h of the onset of in vitro culture in medium that did no t contain the amino acid. These results could, in part, account for th e reduced viability of embryos that develop in vitro and for the benef icial effects of taurine, glutamine, and glycine in culture. We also d etected a decrease in the glutamine, glutamate, and aspartate content of blastocysts as they approached implantation in vivo. These decrease s may result from uterine suppression of the activities of the Na+-dep endent systems that transport amino acids in blastocysts. Regulation o f the levels of these amino acids in and around blastocysts may contri bute to chemical signaling among uterine and embryonal tissues near th e time of implantation.