The mechanisms involved in initiating parturition in mammals are diverse (reviewed in ). However, maturation of the fetal adrenal and increased concentrations of the glucocorticoid cortisol in fetal blood during the last 4-8% of pregnancy have been reported in all mammals studied. In some species, rising fetal cortisol provides a signal to the placenta that is critical for the initiation of parturition. In these species, treatment of the fetus with exogenous cortisol or ACTH leads to premature parturition. In other mammals, such as humans, monkeys, pigs, and rats, increased production of fetal cortisol does not play a clear role, and the mechanisms initiating parturition in these species have been more difficult to characterize. In both groups, however, cortisol from the fetal adrenal provides a stimulus that drives maturation of fetal organ systems. antibiotics levaquin
The stimulus for increased cortisol synthesis by the fetal adrenal before birth originates in the fetal hypothalamus and pituitary, or the placenta, or both. In sheep, production of prostaglandin E2 (PGE2) by the placenta and ACTH by the fetal pituitary increases prepartum.