The Effect of Estradiol-17/β Infusion on the Maintenance of the Induced Corpus Luteum in Cyclic Ewes

Abstract

Fourteen Scottish black-face ewes were injected with 100/zg of prostaglandin analogue (PGF-an) during the luteal phase (days 6—12 of the cycle). The animals were divided at random into 3 groups. Groups 1. 2 and 3 were infused for 8 hours with saline. 3/zg/h. Gonadotrophin releasing hormone (GN-RH) and 3 /zg/h. E2-17/β + 3/zg, h. Gn-RH. respectively, starting 18 hr following PGF-an treatment. Blood samples for hormonal analysis were taken before and at 5. 10. 20. 30. 45. 60. 90. 120 minutes then at 2 hr for 36 hr following the start of infusion.

The mean pretreatment plasma levels of progesterone, estrogen and LH were 2.8 + 1.5 ng/ml, 12.2 + 1.2pg/ml and 1.5 ± 0.25 ng ml. respectively. Eighteen hours following PGF-an treatment, plasma progesterone concentration was significantly (P <0.01) declined (0.43 + 0.5 ng/ml). Administration of estrodiol-17/j prior to Gn-RH (G-III) increased the sensitivity of the pituitary as indicated by peak of LH concentration 67.6 + 36.5 and 134.0 + 26.1 ng/ml for G-II and G-III. respectively.

AU induced corpora lutea (CL) in animals of group 3 were maintained over a 10 day period as compared to none in animals of group 2. Thus the high level of estrogen prior to ovulation may be necessary to maintain the CL in cycling ewes.