Ovine uterine morphogenesis: effects of age and progestin administration and withdrawal on neonatal endometrial development and DNA synthesis.

To determine effects of age and administration and withdrawal of a synthetic progestin (P) on endometrial development and DNA synthesis, ewe lambs were ovariectomized on d 0 (birth) and assigned to one of four groups (n = three/group) that provided (by means of hemihysterectomy) the following uterine tissue types: 1) d 0 control, 2) d 13 control, 3) d 26 control, 4) d 13 after 13 d exposure to P (13P) and 5) d 26 after P exposure from d 0 to 13 (26P). Uterine tissues were processed for histology or explanted with [methyl-3 H] thymidine for autoradiography. Labeling index (LI) was determined for stroma and epithelium in caruncular and intercaruncular endometrial areas and for lumenal and glandular epithelium in uteri with glands. Endometrial glands were absent on d 0, evident at d 13 and well developed by d 26. Day 0 LI was greater (P less than .05) in caruncular than in intercaruncular areas, and greater in stromal than in epithelial tissues. Relationships were reversed in d 13 endometrium (day X endometrial area, P less than .07). Caruncular stromal LI was greater on d 0 than later (P less than .02), whereas intercaruncular epithelial LI was greater after d 0 (P less than .05), but decreased from d 13 to 26 (P less than .05). Glandular epithelial LI was higher on d 13 than on d 26 (P less than .03). Administration of P inhibited endometrial gland development and suppressed d 13P intercaruncular LI (P less than .05). Withdrawal of P was followed by endometrial gland development and increased (P less than .01) intercaruncular epithelial LI in d 26P uteri. Ovary-independent initiation of endometrial gland development involves age- and region-specific alterations in DNA synthesis and could involve negative control.