Preliminary Evidence of Fetal Cortisol Production in Response to Inflammation in a Model of Equine Placentitis

1. Introduction
In a previous study, the hypothalamic-pituitaryadrenal axis (HPAA) in equine fetuses <295 days of age was immature and could not produce cortisol in response to adrenocorticotropic hormone (ACTH).¹  In mares with induced ascending placentitis, prostaglandin F2α and prostaglandin E2 were synthesized in response to pro-inflammatory cytokines and fetal cortisol.²  The objectives were to quantify equine-specific cytokines in chorioallantoic tissue and cortisol concentrations in maternal plasma and fetal fluids from mares with in utero infection, with or without subsequent abortion.

2. Materials and Methods
In 13 adult pony mares, allantoic catheters were placed3 between 260 and 285 days of gestation,³  and mares were allocated to the following five treatments: 1 x 10⁷  CFU Streptococcus zooepidemicus (n = 3), 5.1 x 10⁸ CFU S. zooepidemicus (n = 1), 1 x 10⁷  heat-killed S. zooepidemicus (n = 3), 1 ml sterile phosphate-buffered saline (n = 3), and sham control groups (n = 3). Fetal fluid and maternal plasma were collected every 24 h, and cortisol concentrations were determined by radioimmunoassay. Four areas of the chorioallantois were collected at delivery and stored in RNA stabilization reagent, and expression of 11 equine-specific cytokines was determined.[...]