Temporal changes in the cerebrospinal fluid allopregnanolone concentration and hypothalamic-pituitary-adrenal axis activity in sheep during pregnancy and early lactation

Abstract Research on pregnant mice and rats indicated that a neurosteroid allopregnanolone (AP) might have a stress-protective effect, decreasing the activity of the hypothalamic-pituitary-adrenal (HPA) axis. Using a sheep model in the present research, we tested a hypothesis that the cerebrospinal fluid (CSF) AP concentration changes during pregnancy and early lactation, keeping in check the secretory activity of the HPA axis. Four-hour-long CSF collections (20 μL/min, from 10:00 to 14:00) from the third brain ventricle were conducted in 8 sheep, every 4 weeks, starting from the 28th day of pregnancy until the 28th day after delivery, to determine AP and corticotropin-releasing hormone (CRH) concentrations. A maximum of 8 samples (every 30 min) were gathered from individual sheep. Each series of CSF collections was accompanied by blood sampling every 10 min, to examine the distribution of mean plasma adrenocorticotropin (ACTH) and cortisol concentrations. Six luteal-phase sheep were used as a control during the period corresponding to the first month of pregnancy. The highest AP concentration was noted in the 5th month of pregnancy compared to these in the 1st and 2nd months (P