Exogenous glucocorticoid hormones induce premature birth in tammars accompanied by normal profiles of maternal hormones, so it is possible that fetal cortisol is the trigger for parturition in this marsupial. The tammar may be similar in this regard to species such as the sheep, goat, cow, and rabbit, in which fetal cortisol is directly involved in the onset of parturition, although the mechanism clearly differs between species. proventil inhaler
In these eutherian species, progesterone is necessary for the maintenance of pregnancy, and fetal cortisol leads to its withdrawal before parturition by altering placental steroidogenesis (such as in the sheep) or by inducing luteolysis (such as in the goat). In addition to decreasing progesterone levels, there is an increase in estrogen production by the placenta, and the combined effects of these changes leads to the initiation of parturition. In the tammar, however, progesterone is not necessary for the maintenance of pregnancy once it is established, and the withdrawal of progesterone is not necessary for parturition. Similarly, estrogen does not appear to play a role. In contrast, both prostaglandin and me-sotocin, which increase dramatically at parturition, are necessary for birth.