The invivotransport of14C-α-aminoisobuturic acid into mouse blastocysts during activation for implantation

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Abstract
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, blastocysts were flushed out of the uterus and collected. A distinct uptake of 14C-AIB occurred in the blastocysts 8 h (highest uptake) and 12 h after induction, provided that the in vivo incubation time was 4 h. At these times, blastocysts were lying free in the uterine lumen, and consequently there was a transport of 14C-AIB from the epithelium via the uterine secretion into the blastocysts. Amino acids transported by the system may be important nutrients during early activation. Uptake and retention of 14C-AIB in the uterus was tested at 4 and 8 h after induction of implantation. Highest uptake was observed when 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 uterine tissue was not constant, the metabolic rates for 14C-AIB transport apparently were different for the uterus and the blastocysts. AIB transport into uterine tissue preceded that into the blastocysts. AIB transport into blastocysts was maintained as long as they had a negative surface charge.