Alkaline phosphatase activity in the rat uterus

A COMPARATIVE study of the distribution of placental scars from the first and second pregnancies in laboratory rats indicated that the most posterior scar of first pregnancy tends to be nearer to the cervix than the most posterior second pregnancy scar (Momberg & Conaway, 1956). Frazer (1955) in an earlier study observed that more embryos implanted in the caudal half of the uterus of the rat than in the cranial half when the embryo number was four or less. Momberg & Conaway (1956) found this difference to be greater when the embryo number was high. The reasons for such distributions are not known, but these findings suggest that the uterus varies along its length and does not provide a uniform environ-ment for the implanting embryos. It would further appear that analyses of the various regions of the uterus might furnish information about conditions offering favourable and less favourable environments for the implantation of the blastocysts. Conspicuous alterations in total mass and composition of the rat uterus during the estrous cycle are well established. However, relativel