[The localization of SP1-like substance in the rat placenta by immunohistochemical method]

A protein which reacted with an anti-serum to pregnancy specific beta 1-glycoprotein (SP1) was found in rat placenta by the immunohistochemical method, and is tentatively called SP1-like substance in this paper. By means of a PAP method, the localization of SP1-like substance in the placentae of mice and rats was investigated. Placentae were fixed with 10% neutralized formaldehyde and Bouin's fluid. In mice placentae, SP1-like substance could not be detected with either fixation procedure. In rat placentae, however, the substance was observed to be fixed with Bouin's fluid; the strongly stained substance for anti-SP1 serum was localized at the cytoplasma in tertiary giant cells of the junctional zone near the labyrinth. The animals were examined at 12-13 days, 15-16 days and 19-20 days of gestation. The SP1-like substance was not stained at 12-13 days gestation, but stained weakly at 19-20 days gestation and strongly at 15-16 days gestation in the rat's placentae. These results probably reflect the change in placental aging.