In the golden hamster (Mesocricetus auratus) pseudopregnancy lasts for only 9 or 10 days. If deciduomata are induced during pseudopregnancy they undergo necrosis from Day 8 onwards (Turnbull & Kent, 1963), but if deciduomata are induced in a sterile horn, they are maintained throughout the whole 16 days of the pregnancy (Orsini, 1968). We have shown in an earlier study of hamster pregnancy (Pijnenborg, Robertson & Brosens, 1974) that the spiral arteries of the placental bed and of deciduomata undergo progressive decidualization. The morphological changes can be timed precisely according to the day of gestation; spontaneous necrosis of the decidualized spiral arteries of deciduomata begins on Day 12 and extends to the myometrial segments, but even by term does not involve the medial terminal arteries. At about the time that necrosis begins in the spiral arteries of deciduomata there is a sharp fall in the peripheral plasma progesterone level (Lukaszewska & Greenwald, 1970; Gutknecht, Wyngarden & Pharriss, 1971). It seemed possible that the necrosis could be due to progesterone deprivation, but experiments to test this hypothesis (Pijnenborg et al., 1975) failed to prevent spiral artery necrosis even when the peripheral plasma progesterone level was kept artificially high by daily parenteral injections of progesterone. To investigate the matter further we have compared the deciduomata induced in hamsters in which pseudopregnancy was artificially prolonged and fetal tissue was absent with the deciduomata induced in the sterile horn of unilaterally pregnant hamsters as described earlier (Pijnenborg et al., 1974).
R. Pijnenborg, I. Brosens and W. B. Robertson
R. PIJNENBORG, W. B. ROBERTSON and I. BROSENS
Pregnant hamsters were ovariectomized on Day 7 and daily supplements of progesterone or progesterone plus oestradiol benzoate were given. Fetal development and survival was 14% and 62% respectively. Histological examination indicated that failure of labyrinthine development in the placenta resulted in failure to form an adequate number of maternal arterial spaces communicating with the base of the trophospongium to allow trophoblast migration in the related maternal spiral arteries. Progesterone was essential at all stages of gestation to sustain decidualized tissues and allow survival of a minority of fetuses. Oestradiol supplementation significantly increased fetal survival, but not to normal levels, suggesting that other oestrogens may be essential for the maintenance of normal hamster pregnancy.
R. PIJNENBORG, W. B. ROBERTSON and I. BROSENS
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.