Submitted to: Biology of Reproduction Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2002
Publication Date: December 20, 2002
Citation: Vallet, J.L., Christenson, R.K. 2002. Mifepristone (RU486) treatment on day 2 decreases uterine protein secretion and conceptus diameters on day 11 of pregnancy in swine [abstract]. Biology of Reproduction. 66(Supplement 1):229. (Abstract No. 324) Technical Abstract: Previous results suggested that small conceptuses are associated with decreased embryonic mortality and increased uterine capacity. Furthermore, progesterone treatment on day 2 and 3 of pregnancy increased uterine protein secretion and conceptus estrogen secretion on day 11 and increased fetal weights and decreased uterine capacity at day 105 of pregnancy. Thus, our objective was to determine whether inhibition of progesterone using mifepristone on day 2 could decrease uterine protein secretion and conceptus development on day 11 of pregnancy. White crossbred gilts were observed daily for estrous behavior and were mated after at least one normal estrous cycle (17-23 days). Gilts (n=10 or 11 per treatment) were given either no treatment, 100, 200 or 400 mg of mifepristone in corn oil on day 2 of pregnancy. On day 11 of pregnancy, uterine horns of each gilt were flushed with 20 ml saline. The number and diameters of conceptuses were recorded for each gilt. Uterine flushings were assayed for protein and acid phosphatase activity. The 400 mg dose decreased (P<0.05) average conceptus diameter compared to controls (2.8+/-0.8, 4.9+/-0.7 mm, respectively). Furthermore, mifepristone decreased (P=0.06) total protein in the uterine flush compared to control (45, 65, +/-9 mg, respectively). Acid phosphatase (P<0.05) tended to decrease in the 400 mg-treated gilts compared to controls (3 and 7, +/-8 mg Pi/30 min.ml, respectively). These results suggest that 400 mg mifepristone delayed both uterine protein secretion and conceptus development, and thus, may be useful to increase uterine capacity and litter size in swine.