Secretory Function of the Ovine Uterus: Effects of Gestation and Steroid Replacement Therapy

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Abstract
In Exp. 1, changes in uterine fluid content of protein, calcium and prostaglandin F2α (PGF) were examined between d 30 to 144 of gestation. Volume of uterine fluid (X̅ ± SE) in the nongravid uterine horn of unilaterally pregnant ewes increased (P<.05) between d 30 (8 ± 1 ml) and d 144 (749 ± 46 ml) of gestation. Protein concentration and total protein in uterine fluid also increased (P<.05) between d 30 (2.3 ± .4 mg/ml; 19 ± 7 mg) and d 144 (23.5 ± 3.3 mg/ml; 17.4 + 2.0 g). Total recoverable calcium (mg) in secretions increased from .1 mg (d 30) to over 1.4 g (d 144) due to day of gestation effects (P<.05). Total PGF also increased (P<.01) from 7 ng on d 30 to 15.7 g on d 144. In Exp. II, ovariectomized (OVX) ewes were treated with either corn oil, estrone (E), progesterone (P) or P+E (PE) for 30 d. Treatment with P or PE increased calcium concentration and content (P<.01) in secretions, but differences in uterine fluid volumes and concentrations of protein and PGF were not significant. Treatment of OVX ewes with P stimulated (P<.05) in vitro synthesis of secretory proteins by endometrium, whereas treatment with E enhanced release of unlabeled proteins (P<.05). The major endometrial secretory proteins were identified in allantoic fluids from d 60 to term and were detected along the mesenchymal border of the chorioallantois using immunohistochemistry. Results from this study indicate that P may be a primary hormone regulating accumulation of fluid, protein, calcium and specific endometrial proteins in the uterine lumen during gestation, and that uterine milk proteins gain access to the fetal-placental unit.