Biology of Reproduction, Vol 3, 214-217, Copyright © 1970 by Society for the Study of Reproduction

Luteolytic Action of Intrauterine Devices in Sheep as Affected by Duration of Progesterone Influence and By the Age of the Corpus Luteum

¹ Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706

A test was made to determine whether the luteolytic action of intrauterine devices in sheep depends on the age of the corpus luteum or on the duration of progesterone influence. Insertion of the IUD on day 2 but not on day 7 of the estrous cycle caused regression of the corpus luteum. Gonadotropin treatment on day 5 of the cycle induced a new corpus luteum and an IUD was inserted into each uterine horn on day 7. The IUD caused regression of the induced corpus luteum if the corpus luteum of the cycle was removed at the time of insertion of the IUD; the IUD did not cause regression of the induced corpus luteum if either the corpus luteum of the cycle was left intact or if, after its removal at the time of insertion of the IUD, the ewe was injected with progesterone for 6 days. Treatment with progesterone did not prevent regression of the corpus luteum of the cycle, however, if it was begun when the IUD was inserted on day 2 of the cycle. It seems that the luteolytic effect of the IUD is reduced by the action of progesterone over an appreciable period of time before the insertion of the IUD and by a continuation of its action during the time the IUD is in place.