In eutherian mammals, interactions between the fetal hypothalamic-pituitary-adrenal (HPA) axis and the placenta stimulate the fetal adrenal at term, and results reported here provide evidence for a similar mechanism in the tammar wallaby. Production of PGE2 by the placenta at the end of pregnancy in the sheep provides an important trophic drive to the fetal HPA axis, and the resulting increase in cortisol stimulates further PGE2 release, creating a positive feedback loop. Prostaglandin synthesis by the tammar placenta and endometrium increases over the last 2 days of pregnancy, paralleling fetal cortisol concentrations. Cortisol synthesis by the fetal adrenal of the tammar is stimulated by PGE2 in vitro, suggesting an adrenocorticotrophic role for increased placental PGE2 production during parturition in this marsupial. Cortisol synthesis by the fetal adrenal in vitro is also stimulated by ACTH, which suggests that the corticotrophs in the pituitary may stimulate cortisol as in eutherians. Cheap Diskus Advair
Previous studies have clearly shown that the tammar fetus sets the timing of its own birth and that synthetic glucocorticoids initiate a physiologically normal, but premature, parturition in the tammar. Cortisol production by the fetal adrenal increases progressively over the last 3 days of pregnancy. Placental PGE2 and ACTH released from the fetal pituitary may contribute to this adrenal stimulation, which results in the accumulation of large amounts of cortisol in YSF, allantoic fluid, and fetal plasma. Taken together, our results suggest that endogenous cortisol of fetal adrenal origin provides the stimulus for spontaneous parturition in this marsupial species.