Role of peroxisome proliferator-activated receptor γ in corpora lutea of pseudopregnant rabbits

The peroxisome proliferator-activated receptors (PPARs), afamily of three (a, d, g) nuclear receptor/transcription factors,are involved in critical processes of ovarian function, such assteroidogenesis, angiogenesis, and apoptosis. PPAR agonistspresent contradictory actions on granulosa and luteal steroidsecretion. To this end, experiments were devised to examine byimmunohistochemistry the occurrence of PPARgin rabbit CL(days 4 and 9 of pseudopregnancy) as well as its effects on theendocrine activity using PPARg agonist (15d-PGJ2) andantagonist (T0070907)in vitro. To evaluate the role of PPARgon the acquisition of luteal capacity to PGF2a, the dynamicchanges in gene expression for PPARg were analyzed by RT-PCR in day 4 and 9 CL after PGF2a analogue (alfaprostol)injection. Immunohistochemical results revealed that PPARgwas localized in the cytoplasm and nuclei of luteal cells. Inboth luteal stages, PPARg agonist increased (p < 0.01)progesterone and decreased (p < 0.01) PGF2ain vitrosecre-tion, while the antagonist showed an opposite effect. In day 9CL, PGF2a determined a PPARg mRNA down-regulation(p < 0.01). This study indicates that PPARg acts as aluteotrophic factor by affecting the endocrine activity of rabbitCL and that PGF2a regulates luteolysis in day 9 CL also viaPPARg gene expression modulation.