THE CORPUS LUTEUM OF THE SHEEP: EFFECT OF THE CONCEPTUS ON LUTEAL FUNCTION AT SEVERAL STAGES DURING PREGNANCY

Abstract

SUMMARY The relationship between the conceptus and the corpus luteum during the first 90 days of pregnancy was determined in sheep which were made unilaterally pregnant by egg transfer 4 or 5 days after oestrus. Additional corpora lutea were established approximately 24 hr. after an injection of human chorionic gonadotrophin given on day 20, 30, 50 or 70, and 18–24 days later the sheep were killed. When 17 unilaterally pregnant ewes, in which new corpora lutea had been induced on or before day 31, were killed, only the corpora lutea on the same side as the gravid horn were still functional; total regression of the corpora lutea had occurred in the ovary adjacent to the non-gravid horn. In 13 out of 14 sheep in which corpora lutea had been induced on day 51 or 71, the luteal tissue was still present in both ovaries at autopsy. Thus a local effect is exerted during the first one-third of pregnancy by conceptuses confined to one uterine horn, but this effect changes to a more general one about day 50. In five sheep, embryos were allowed to develop in an intact uterus and under these conditions no unilateral effect could be demonstrated on corpora lutea induced on day 31.