The development of the uteroplacental vascular system in the golden hamster Mesocricetus auratus.

The development of the uteroplacental vasculature in the golden hamster was studied by vascular casting and India ink injection methods. The hamster placenta usually has three sets of uteroplacental arteries and its maternal segment is derived from the medial arterial division of the non-pregnant uterus. The maternal segment consists of the spiral artery in the endometrium and the vascular knot in the mesometrium. The spiral arteries start developing on Day 5, simultaneously with the endometrial decidual reaction of the mesometrial side. The chorioallantoic placenta of the golden hamster is the so-called labyrinthine haemochorial type. The formation of the haemochorial placenta begins as early as Day 7, when maternal blood drains into the uterine lumen to form the maternal blood space. In this space, the maternal blood starts flowing on Day 8 and a direct contact with the chorion containing fetal capillaries is achieved on Day 9. The labyrinthine feature, in which the direction of flow of the maternal and fetal blood is in opposite directions, is achieved on Day 10. This countercurrent system functions through the central arterial space, the fetal segment of the uteroplacental artery which leads the maternal blood to the antimesometrial surface of the labyrinth.