The inflammatory state of the rat placenta increases in late gestation and is further enhanced by glucocorticoids in the labyrinth zone.

INTRODUCTION: Inflammation plays central roles in key aspects of successful reproduction: ovulation, implantation and parturition. In this study we characterised the inflammatory profile of the rat placenta in late gestation with and without maternal glucocorticoid (dexamethasone) treatment.
METHODS: Placentas (n = 6/group) were collected from untreated (Con) rats at days 16 and 22 (term = day 23) and from dexamethasone-treated (Dex) rats at day 22. mRNA and protein expression was determined for enzymes of prostaglandin synthesis and metabolism (Ptgs-1, Ptgs-2, 15-Pgdh), pro-inflammatory cytokines (Tnf-α, Il-1β, Il-6), and the macrophage marker Emr-1 in the junctional (JZ) and labyrinth (LZ) zones of the placenta.
RESULTS: Tnf-α, Il-1β and Il-6 mRNAs all increased (2- to 4-fold) in both placental zones between days 16 and 22 (P < 0.01). Ptgs-2 mRNA (30-fold; P < 0.01) and PTGS-2 protein (2.4-fold; P < 0.05) similarly increased in LZ. In contrast, 15-Pdgh expression increased in JZ but decreased in LZ; these changes were accompanied by decreased levels of PGE2 in the JZ and a trend towards increased LZ levels. Dex treatment inhibited fetal and placental growth, but had minimal effects on expression of Ptgs-1, Ptgs-2 or 15-Pdgh. Nevertheless, Dex treatment increased LZ PGE2 levels (5-fold, P < 0.01) at the end of gestation. Dex treatment increased Tnf-α mRNA expression in LZ (40%; P < 0.05), but modestly suppressed cytokine protein expression in JZ.
CONCLUSIONS: These data demonstrate that the inflammatory state of the LZ increases near term coincident with the known increase in local glucocorticoid levels. This suggests the classic anti-inflammatory actions of glucocorticoids do not occur in the placental LZ.