Peroxisome proliferator activated receptor ligands affect porcine endometrial steroids production during the estrous cycle and early pregnancy: an in vitro study

In the present study, we investigated the effect of PPAR ligands on progesterone (P4) and 17β-estradiol (E2) secretion, as well as 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4) isomerase (3β-HSD) mRNA expression, in porcine endometrial slices collected on days 10-12 and 14-16 of the estrous cycle or early pregnancy. The explants were incubated in vitro for 6 h in the presence of PPARα ligands - WY-14643 (agonist) and MK 886 (antagonist); PPARβ ligands - L-165041 (agonist) and GW 9662 (antagonist); PPARγ ligands - 15d-prostaglandin J2 and rosiglitazone (agonists) and T0070907 (antagonist). During the estrous cycle, all PPAR ligands inhibited P4 secretion during the mid-luteal phase (days 10-12). During early pregnancy, a stimulatory effect of PPARα agonist was observed during maternal recognition of pregnancy (days 10-12), while an inhibitory effect was observed at the beginning of implantation (days 14-16). PPAR ligands inhibited the expression of 3β-HSD mRNA on days 14-16 of the estrous cycle (β and γ isoforms) or pregnancy (α, β, γ isoforms) but did not affect gene expression on days 10-12 of the estrous cycle or early pregnancy. An inhibitory effect of PPARα, PPARγ, and PPARβ on E2 secretion was observed during maternal recognition of pregnancy, but a stimulatory effect was observed during mid- (γ isoform) or late-luteal (β isoform) phases of the estrous cycle. Our study indicates, for the first time, that PPARs are engaged in P4 and E2 production in porcine endometrium. It is possible that the diverse receptivity of endometrial tissue to the PPAR ligands can be associated with the reproductive status of gilts.