A study of proliferative activity of the uterine epithelium of the pregnant rat in relation to the morphogenesis of the "new" lumen.

areas between conceptuses As the chorioallantoic placenta forms towards the mesometrial aspect, a new lumen extends around the antimesometrial aspect of the implantation (Text-fig. 1), and from about Day 12 it connects the interconceptual lumina from either side. Some of the proliferative characteristics involved in the morphogenesis of the `new' uterine lumen are examined here. The Wistar rats used were primigravidae, aged 3 to 6 months, and Day 0 of pregnancy was defined as the day on which spermatozoa were seen in the vaginal smear. The rats were given tritiated thymidine (1 \g=m\Ci/gbody wt, sp. act. 5 Ci/mmol: Radiochemical Centre, Amersham, England) intraperitoneally or intravenously on Days 9, 11, 12, 13, 14, 15, 16 or 18 of pregnancy and were killed 1 hr later. Usually, at least three conceptuses were examined at each stage of pregnancy but they were not necessarily from the same animal. Tissues were fixed in buffered formol saline or Carnoys fixative. Autoradiographs were prepared using Ilford K5 emulsion and Kodak D19 developer. The percentage of labelled cells in transverse sections of the uterus was determined for each of three categories of the uterine epithelium. For the first category, approximately 200 glandular epithelial cells were counted regardless ofwhether the glands were in regions ofor between conceptuses; for the second, epithelial cells lining the whole luminal surface of a section of uterus between conceptuses were counted ; for the third, a count was made of all epithelial cells which lined the outer aspect of the 'new' lumen as it extended around the conceptus. The number of cells in the third category varied from 50 (in a section of the furthermost extension at Day 9) to about 4000 at Day 18. The epithelial cells covering the antimesometrial decidua had an atypical appear¬ ance and have been described elsewhere (Bulmer & Peel, 1974). Table 1 shows that very few glandular epithelial cells were labelled at each stage examined. In contrast, the percentage of labelled surface epithelial cells in interconceptual areas between Days 9 and 13 was between 10 and 20%.