Summary. Corpora lutea and ovarian stromal tissue were anlaysed for prostaglandin (PG) concentrations and activities of enzymes involved in PG metabolism at 8, 10, 12, 13 and 15 days after induction of ovulation. In CL of pseudopregnant rabbits, the PGE-2–9-ketoreductase (PGE-2–9-KR) was highly active on Days 10, 12 and 15 when compared with Day 8 (P < 0·01; P < 0·001; P < 0·05). In pregnant animals PGE-2–9KR activity was only increased on Day 12 (P < 0·05) but declined to basal levels on Days 13 and 15. Comparing PGE-2–9-KR activity of pseudopregnant and pregnant animals, a significant elevation was found on Day 15 of pseudopregnancy (P < 0·025). Activities of PG-15-hydroxydehydrogenase did not exhibit any significant changes with time in pseudopregnant or pregnant rabbits.
PGE-2 concentrations were increased on Days 12, 13 and 15 (P < 0·025) when compared with Day 8. Changes in PGF-2α concentrations paralleled those of PGE-2–9-KR. The concentrations of PG metabolites 13,14-dihydro-15-keto-PGE-2 and -PGF-2α were lower than those of the primary PGs and did not show stage-specific changes in pseudopregnant and pregnant animals.
These results demonstrate that the rabbit CL posesses enzymes to convert PGE-2 to PGF-2α and to metabolize both PGs. PGE-2–9-KR may be involved in regulating the PGF-2α/PGE-2 ratio and possibly in controlling the life-span of the corpus luteum.
Keywords: PGE-2-9-ketoreductase; prostaglandin-15-hydroxydehydrogenase; luteolysis; prostaglandin metabolism; pseudopregnancy; rabbit