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Accessory deciduomata in artificially prolonged pseudopregnancy in the golden hamster

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).