Abstract
The objective of this experiment was to determine the effect of mifepristone, a progesterone receptor antagonist, on pregnancy and secretion of steroids, pregnancy-specific protein B (PSPB) and prostaglandins at mid-pregnancy in ewes. Ninety-day pregnant ewes were ovariectomized (OVX) and treatments were initiated 72 h post-OVX. Ewes received (1) vehicle, (2) prostaglandin F 2α (PGF 2α, 8 mg/58 kg/bw, i.m.) 84 h post-OVX, (3) mifepristone (50 mg intrajugular at 72, 84, 96, and 108 h post-OVX), (4) mifepristone (50 mg)+ PGF 2 α , (5) mifepristone (100 mg intrajugular at 72, 84, 96, and 108 h), and (6) mifepristone (100 mg)+ PGF 2 α . Ewes treated with vehicle or PGF 2α alone did not abort ( P≥0.05). But, 60, 80, 60, and 100% of ewes treated with mifepristone (50 mg), mifepristone (50 mg)+ PGF 2 α , mifepristone (100 mg), and mifepristone (100 mg)+ PGF 2 α , respectively, aborted ( P≤0.05). Profiles of progesterone, estradiol-17β, prostaglandin E (PGE), or PSPB did not differ ( P≥0.05) among treatment groups. Profiles of PGF 2α of treatment groups receiving mifepristone with or without PGF 2α differed ( P<0.05) from vehicle or PGF 2α alone-treated ewes. It is concluded that progesterone actions are necessary to suppress uterine/placental secretion of PGF 2α and that maintenance of critical progesterone: estradiol-17β and PGE:PGF 2α ratios are necessary for maintenance of pregnancy.
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