Effects of Intrafollicular Injections of Prostaglandins in Non-Pregnant and Pregnant Ewes

Abstract

Responses to three doses of prostaglandin (PG)F2α (100, 150 and 200 jug) and a single dose (200 µg) of PGF1α, PGE2 and arachidonic acid or buffer injected on day 9 into the largest follicle on the ovary with the corpus luteum were compared in groups of six non-pregnant unilaterally-ovulating ewes. Jugular venous plasma was collected at 0 time and .5, 1, 4 and 24 hr post-injection. Only ewes treated with PGF2α returned to estrus within 72 hr after injection (200 µg, 4 of 6; 150 µg, 3 of 6; 100 µg, 1 of 6). Progesterone concentrations in ewes treated with PGF2α did not differ among doses or from controls at 0 and 4 hr, while at 1 hr all ewes treated with PGF2α had values lower than control ewes. At 24 hr, ewes treated with 150 µg PGF2α had lower progesterone than control ewes or ewes receiving 100 µg PGF2α:- Progesterone concentrations in ewes treated with PGF1α or arachidonic acid did not differ from those in control ewes. Ewes treated with PGE2 had higher progesterone than control ewes at 4 hr and exceeded ewes in all other groups at 24 hours. Estrone and estradiol-17β did not vary with treatment or time in ewes receiving buffer, 200 µg PGF2α or 200 µg PGF1α. A single large follicle in each ovary bearing corpora lutea in each of 17 mated and 14 non-mated ewes was injected with 200 µg PGF2α on day 12. Jugular venous blood was collected at 0 time and 1, 4 and 24 hr post-injection. Mated ewes were sacrificed to check for embryos in the uterus as they returned to estrus or on days 17 to 22. Progesterone declined similarly in non-mated ewes (14), mated ewes with no embryos (9) and mated ewes with embryos (8), except that some apparent recovery was seen by 24 hr in pregnant ewes. In non-mated ewes and mated ewes without embryos, 11/14 and 8/9 returned to estrus early and mean intervals from treatment to estrus were 2.9 and 2.4 days, respectively. Five of eight ewes with embryos did not return to estrus, and two of the three returning to estrus had small embryos believed to have stopped developing before injection of PGF2α It is suggested that a factor from the conceptus overcomes the luteolytic effect of PGF2α in sheep.