Migration of leucocytes into the uterus after acute removal of ovarian progesterone during early pregnancy in the sheep.
The effects of acute deprivation of progesterone during early pregnancy on the occurrence of maternal leucocytes in uterine tissues was studied in sheep. Ovariectomy on day 21 of pregnancy resulted in a rapid influx of polymorphonuclear (PM) leucocytes into both caruncular and intercaruncular (glandular) endometrium but not into the myometrium. The infiltration had commenced by 24 hours after ovariectomy when the fetal membranes appeared histologically normal. By 72 hours after ovariectomy infiltration of PM leucocytes and degradation of the fetal syncytium were severe and extensive. The effect was specifically due to progesterone deprivation in pregnant animals since it was not seen in progesterone-treated ovariectomized pregnant animals or in non-pregnant animals ovariectomized in the mid luteal phase of the oestrous cycle. The PM leucocyte influx was not associated with changes in the number of intra-epithelial lymphocytes, the occurrence of which was only slightly reduced at the time of attachment. The results implicate maternal progesterone as a local anti-inflammatory agent within the gravid uterus and also show that total expulsion of lymphocytes from uterine epithelia at implantation is not a mechanism for immunoprotection of the sheep fetal allograft.