Prostaglandin E1 or E2 inhibits an oxytocin-induced premature luteolysis in ewes when oxytocin is given early in the estrous cycle

Abstract The objective of this study was to determine whether PGE 1 or PGE 2 prevents a premature luteolysis when oxytocin is given on Days 1 to 6 of the ovine estrous cycle. Oxytocin given into the jugular vein every 8 hours on Days 1 to 6 postestrus in ewes decreased (P ≤ 0.05) luteal weights on Day 8 postestrus. Plasma progesterone differed (P ≤ 0.05) among the treatment groups; toward the end of the experimental period, concentrations of circulating progesterone in the oxytocin-only treatment group decreased (P ≤ 0.05) when compared with the other treatment groups. Plasma progesterone concentrations in ewes receiving PGE 1 or PGE 1 + oxytocin were greater (P ≤ 0.05) than in vehicle controls or in ewes receiving PGE 2 or PGE 2 + oxytocin and was greater (P ≤ 0.05) in all treatment groups receiving PGE 1 or PGE 2 than in ewes treated only with oxytocin. Chronic intrauterine treatment with PGE 1 or PGE 2 also prevented (P ≤ 0.05) oxytocin decreases in luteal unoccupied and occupied LH receptors on Day 8 postestrus. Oxytocin given alone on Days 1 to 6 postestrus in ewes advanced (P ≤ 0.05) increases in PGF 2α in inferior vena cava or uterine venous blood. PGE 1 or PGE 2 given alone did not affect (P ≥ 0.05) concentrations of PGF 2α in inferior vena cava and uterine venous blood when compared with vehicle controls or oxytocin-induced PGF 2α increases (P ≤ 0.05) in inferior vena cava or uterine venous blood. We concluded that PGE 1 or PGE 2 prevented oxytocin-induced premature luteolysis by preventing a loss of luteal unoccupied and occupied LH receptors.