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Inhibition by Progesterone of IUD-Induced Luteal Regression in the Ewe

U.S. Department of Agriculture,¹ Beltsville, Maryland 20705

Abstract

OVULATION was induced on day 5 of an estrous cycle and each uterine horn was infected with E. coli or implanted with a plastic spiral on day 7. Both the original and the induced CL regressed in response to the infection. However, neither the original nor the induced CL regressed after the insertion of the IUD, even though 2-day-old CL are ordinarily susceptible to IUD-induced luteolysis. The results suggested that progesterone secretion by the original CL prevented IUD-induced regression of the new CL.

The injection of progesterone on days 1 to 4 of the estrous cycle prevented luteal regression following the insertion of an IUD on day 3. Also, the injection of progesterone on days 4 to 6 tended to counteract the enhancing effect of estradiol on CL regression after the insertion of an IUD on day 5. These results indicate that progesterone can prevent IUD-induced luteolysis in the ewe.

¹ Animal Science Research Division, A.R.S., Agricultural Research Center. Supported in part by the National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland.