Local Auto-Amplification System for Prostaglandin F2alpha in Bovine Corpus Luteum.

Abstract

It has been considered that regression of the corpus luteum (CL) is induced by positive feedback loop between uterine prostaglandin F2a (PGF) and luteal oxytocin (OT) in ruminants. However, a previous study showed that an injection of PGF together with an OT receptor antagonist also induced luteolysis with an increase of plasma PGF level. Furthermore, administration of PGF in vivo dramatically increased the PGF production of ovine CL tissue. These findings suggest that PGF stimulates intraluteal PGF production, and that the possible auto-amplification system for PGF production plays an important role in luteolysis. However, it is not clear whether PGF directly stimulates intraluteal PGF production and which PGF synthetic enzymes are involved in PGF-stimulated PGF biosynthesis. In the present study, we examined the effects of PGF 1) on PGF and PGE production in bovine luteal tissue, and 2) on PGF biosynthetic enzymes such as cyclooxygenase (COX)-2, PGF synthase (PGFS) and carbonyl reductase (CBR)-1 in bovine mid luteal cells. Luteal tissues were collected at the early (Day 2-3), developing (Days 5-6), mid (Days 8-12) and late (Days 15-17) luteal stages. These tissues were exposed to PGF (1 μM) or PGF together with a COX inhibitor (indomethacin: 10 μM) for 2 h, and then washed with PBS 6 times to remove the treated PGF2. The tissues were cultured further for 2 h. PGF stimulated intraluteal PGF production in all stages but did not affect PGE2 production. The stimulatory effect of PGF was greatest at the late luteal stage. Indomethacin suppressed the PGF-stimulated PGF production in luteal tissue, indicating that the increased PGF in the medium was luteal origin. The protein expression of COX-2, PGFS and CBR-1 were determined by western blotting in cultured bovine luteal cells obtained from the mid CL. Cells were treated for 4 or 24 h with PGF (1 μM). PGF significantly increased PGFS and CBR-1 expression (P<0.05), and tended to increase COX-2 protein level (P=0.06) at 24 h post-treatment. The overall results strongly suggest the presence of a local auto-amplification system for PGF that is mediated by PGFS, CBR-1 and COX-2 activation.