Effect of prostaglandin F2 α ( PGF2 α) on sources of progesterone and pregnancy in intact, ovariectomized and hysterectomized 90–100 day pregnant ewes

Abstract

A single dose of 8 or 16 mg of PGF 2 α per 58 kg body weight was injected intramuscular into intact, ovariectomized or hysterectomized 90–100 day pregnant sheep in three separate experiments. Both doses of PGF 2 α decreased the weights of the corpora lutea ( P≤0.05) and the concentration of progesterone in ovarian venous plasma at 72 hr ( P≤0.05) compared to the 0 hr sample within treatment groups and to control ewes at 72 hr in intact and hysterectomized pregnant ewes. In hysterectomized pregnant ewes, progesterone in jugular plasma declined ( P≤0.05) from 0 to 72 hr but never fell below 4 mg/ml and this decrease in progesterone after 8 or 16 mg PGF 2 α was greater than in control hysterectomized ewes ( P≤0.05). There was a significant decrease in progesterone over time in jugular or uterine venous plasma in the presence of absence of the ovaries in 90–100 day pregnant ewes ( P≤0.05) but the profiles of progesterone were not different between vehicle and PGF 2 α -treated ewes ( P≥0.05). Uterine venous progesterone never declined below 30 ng/ml in the presence or absence of the ovaries and there was a significant quadratic increase ( P≤0.05) in uterine venous progesterone toward the end of the 72 hr sampling period indicating an increase in steroidogenic activity of the placenta. PGF 2 α did not affect the number of abortions in intact or ovariectomized pregnant ewes ( P>0.05). Thus, the corpus luteum of sheep at 90–100 days of pregnancy is functional and responsive to PGF 2 α , placentomes are functional but do not appear to be responsive to the doses of PGF 2 α tested and PGF 2 α was not an abortifacient over the 72 hr treatment period.