The Effect of 17β-Estradiol on Corpus Luteum Function in Sheep1

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Abstract
Twenty cycling ewes received daily injections of 17β-estradiol and were autopsied on Day 10, 15, 22, or 37 after the beginning of estrus. Estrogen treatment consisted of 2.0 mg on Day 4 and daily injections of 2.5 mg from Day 5 through the day preceding autopsy or to Day 22. Thirteen control ewes which received no injections were autopsied on Days 10 or 15. Estradiol induced reovulation and corpus luteum (CL) formation in 80% of the ewes treated and inhibited follicular development for as long as 2 weeks after termination of treatment. Ovarian plasma and CL progesterone levels and pituitary luteinizing hormone (LH) levels were determined for control and estradiol-treated ewes on Day 10 of the estrous cycle. In addition, plasma LH was estimated on Day 10 of the cycle in control and estrogen-treated ewes. Estradiol treatment maintained the CL to at least Day 37. Estradiol appeared to initially depress progesterone production since total CL progesterone was significantly greater in control ewes on Day 10 then treated ewes at Day 10, 15, or 22. Fifteen days after the cessation of estradiol injections (Day 37) high CL progesterone levels were associated with a decrease in ovarian vein progesterone concentration suggesting possible progesterone retention by the CL or possible, but unobserved, dramatic changes in rate of blood flow. Estrogen treatment caused a decrease in pituitary LH in all treated groups when compared with control ewes at Day 15 and an apparent increase in plasma LH when measured at Day 10. These results indicate that, at least under the conditions of this experiment, in the ewe, estradiol exerts both a luteotropic and luteolytic influence.

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