The in vivo transport of 14C-alpha aminoisobuturic acid into mouse blastocysts during activation for implantation.

The in vivo transport of 14C-AIB (14C-alpha-aminoisobuturic acid) into mouse blastocysts was studied during activation for implantation. Mice, kept in experimentally delayed implantation, were given estrogen to induce implantation and then injections of 14C-AIB i.v. at 0, 4 and 8 h after the estrogen. After in vivo incubation times for 1/3 or 4 h with the labeled amino acid the blastocysts were flushed out of the uterus and collected. A distinct uptake of 14C-AIB occurred in the blastocysts 8 h (the highest uptake) and 12 h after the induction, provided that the in vivo incubation time was 4 h. At these times the blastocysts are lying free in the uterine lumen and consequently there is a transport of 14C-AIB from the epithelium via the uterine secretion into the blastocysts. This uptake indicates that amino acids transported by the system A are important nutrients during early activation. The uptake and retention of 14C-AIB in the uterus was tested at 4 and 8 h after the induction of implantation. The highest uptake was observed when the labeled amino acid was given at 8 h while the longest retention time occurred when 14C-AIB was given at 4 h. Since the transport ratio between the blastocysts and the uterine tissue is not maintained constant it is concluded that the metabolic rates for 14C-AIB transport are different for the uterus and the blastocysts. The AIB transport into uterine tissue preceeds that into the blastocysts. The AIB transport into the blastocysts is maintained as long as they have a negative surface charge.