The arterial migration of trophoblast in the uterus of the golden hamster, Mesocricetus auratus.

Abstract

Summary. Fifty pregnant golden hamsters, twenty of which were unilaterally pregnant and had deciduomata induced in the sterilized horn, were studied. Conceptuses, without the fetus, and deciduomata were examined histologically from Day 7 to term, Day 16. Special attention was directed towards trophoblast arterial migrations, structural changes in maternal vessels before and during trophoblast migration, and the interaction between trophoblast and maternal vascular tissue. Changes occurred in the maternal vessels during pregnancy which were independent of trophoblast influence; they included the formation of stromal sheaths that became decidualized and were accompanied by intramural stromal granulocyte proliferation. These changes were identical in time and sequence in a conceptus and a deciduoma and were probably mediated by the altered hormonal and haemodynamic status of pregnancy. In a conceptus, there were two separate waves of retrograde arterial trophoblast migration, the first by way of the circumferential system between Days 8 and 12 to the mesometrial triangle, and the second from Day 12 onwards by way of the central spiral arteries and the medial terminal arteries. The first circumferential migration provoked an inflammatory cellular response in the mesometrial triangle whereas the second migration resulted in the transformation of the central arterial supply, as far as the medial terminal arteries, to a series of distended fibrinoid tubes. In the absence of trophoblast, the central arterial supply in deciduomata underwent spontaneous necrosis at the time when the central trophoblast migration was taking place in the conceptus. The results are discussed in relation to the alterations in hormonal status and haemodynamics consequent upon pregnancy and the reaction of trophoblast with maternal blood vessels in relation to possible local hormonal influences and immunological reactions. The general conclusion is that hamster pregnancy, under properly controlled experimental conditions, is a useful model for the study of fundamental mechanisms in haemochorial placentation.