Endocrine Abstracts

The morphology of individual ovine placentomes is known to be influenced by several factors including; hypoxia (Gardner et.al, 2002, Placenta 23:459-466), heat stress (Bell et.al, 1987, J.Dev.Phys. 9:17-29) and the fetal and maternal nutrition (McCrabb et.al, 1991, B.J.Nutrition 65:157-168). These conditions are associated with elevated fetal plasma cortisol concentrations. However, the direct effects of fetal cortisol on placental morphology remain unknown. Hence, this study investigated the regulation of ovine placental morphology by cortisol during late gestation.

Under general anaesthesia, intra-vascular catheters were inserted into 33 Welsh Mountain sheep fetuses between 115-118 days of gestation (term ~145days). Up to 3 placentomes, typical of the population present, were tagged per animal by suturing tubing to the placentome membranes. Tagged placentomes were classified as A, B, C, or D-types (least everted to most everted fetal trophectoderm) using the criteria of Vatnick et.al 1991 (J.Dev.Phys. 15:351-356). At least 6 days after surgery, fetuses were infused i.v. with either cortisol (n=16, 2-3mg/kg/day Efcortisol) or saline (n=17, 0.9% w/v NaCl, 2.4 ml/day). After 5 days, ewes and fetuses were euthanased (Lethabarb, 40 mg/kg i.v.). The tagged placentomes were also re-classified and total placental weight measured. Fetal plasma cortisol concentrations were determined by radioimmunoassay. Mean values (±SE) of fetal plasma cortisol (nanograms per millilitre), placental weight (grams) and changes in placentome type between measurements are given below.

Cortisol infusion raised fetal cortisol levels at delivery in all animals (66.4±6.8; P<0.001; Student's t-test), relative to saline-infused controls (16.9±1.4). There was no significant difference in total placental weight between saline (320±13) and cortisol infused (296±11) fetuses. Overall, there were significantly fewer placentomes showing increased eversion (A to D direction) in cortisol (7 observations), than saline infused animals (21observations; P<0.001; Chi-Squared test). Using a tagging technique, this is the first study to show that cortisol affects the gross morphology of individual ovine placentomes. The mechanisms by which cortisol acts and the functional significance of the morphological changes remain to be determined.