In humans, corticotropin-releasing factor produced at the end of pregnancy by the placenta appears to provide this stimulus. In both species, synthesis of adrenal trophic factors by the placenta is increased by cortisol, providing a positive feedback system that leads to a rapid response by the fetal adrenal. ampicillin antibiotic
In the tammar wallaby, glucocorticoids and the fetal adrenal appear to play a role in the initiation of parturition. The adrenal cortex of the fetus differentiates on Day 21 of the 26-day pregnancy, and its steroidogenic enzymes are active on Day 22. Presumptive corticotrophs are present in the pituitary of the tammar neonate, and it is possible that ACTH is being produced by the fetus. The synthetic glucocorticoid dexamethasone induces premature birth, and cortisol can be detected in fetal blood on Day 25 of pregnancy. Glucocorticoids are also involved in maturation of the lungs of the tammar wallaby fetus. Thus endogenous cortisol of fetal origin may provide the trigger for parturition in this marsupial. The choriovitelline (yolk sac) placenta of the tammar wallaby produces increasing amounts of PGE2 and PGF2a at the end of gestation, and it is likely that this enters the fetal and maternal circulation. Fetal pituitary ACTH and placental PGE2 could thus provide a prepartum stimulus for adrenal corticosteroid production.
The aim of this study was to examine cortisol production during the peripartum period in the tammar wallaby. The concentration of cortisol in fetal fluids and adrenal tissue during late pregnancy was measured, and the in vitro production of cortisol by the fetal adrenal was examined. The potential for ACTH and PGE2 to stimulate this production was also evaluated.