Fetal-maternal adrenocortical activities approaching parturition in mice

The temporal profile of fetal-maternal adrenocortical activities, including blood corticosterone concentration and adrenal expression of cytochrome P45011ß, approaching parturition was investigated in mice. The fetal serum corticosterone concentration reached a peak on gestational day (G) 17 and maternal serum corticosterone reached a highest value on G15 and then subsequently decreased. Fetal and maternal adrenal expression of cytochrome P45011ß increased with advancing pregnancy before the blood corticosterone concentrations reached each peak but then did not change substantially until the term. The results suggest that the increases of blood fetalmaternal corticosterone concentrations before peak are contributed by the increased adrenocortical activities, whereas the subsequent drops after peaks are not adrenocortical dependent. Other possible factors responsible for the drop such as placental catabolism, tissue utilization and liver metabolism are discussed.