Prostaglandin F and 13,14-dihydro-15-keto prostaglandin F in the endometrium and uterine flushings of sheep before implantation.

The concentrations of prostaglandin F (PGF) and its major metabolite, 13,14-dihydro-15-keto prostaglandin F-2 alpha (PGFM), were measured in caruncular and intercaruncular endometrium of pregnant and non-pregnant ewes on Days 9, 11, 13 and 15 after mating (Day 0) and related to the content of PGF and PGFM in the uterine flushings. The tissue concentrations of PGF and PGFM increased with time after mating particularly on Days 13 and 15 and to a greater extent in pregnancy. However, the ratio of PGF to PGFM remained constant at 0.7, except on Day 15 in non-pregnant endometrium when it fell to 0.3 (P less than 0.05), suggesting that synthesis rather than metabolism was limiting tissue concentrations of PGs. The changes in tissue concentrations of PGF and PGFM were reflected in the contents of PGF and PGFM in the uterine flushings of non-pregnant, but not pregnant ewes. Pregnant ewes had relatively more PGF and less PGFM than did non-pregnant ewes on Day 15. Moreover, there was always 5-10-fold less PGFM than PGF in the uterine flushings. It is concluded that the increase in PG in the uterine lumen in pregnancy has its origin in the blastocyst, and that pregnancy may be associated with an increase in the synthesis and retention of PGs in the endometrium, rather than a redistribution towards the uterine lumen away from the uterine venous drainage.