A ROLE FOR GLUCOCORTICOIDS IN PARTURITION IN A MARSUPIAL, MACROPUS-EUGENII

Dexamethasone treatment induces premature birth in tammar wallabies. T reatment was administered at one of three times between 1200 h on Day 24 and 0930 on Day 25, and birth occurred 22.8 +/- 0.5 h later, signif icantly earlier than the time of birth for controls, which was 47.7 +/ - 2.3 h after treatment. The neonates from treated females were signif icantly lighter than control neonates (360 +/- 9 vs. 413 +/- 5 mg), an d 60% of these died within 12 h of birth, suggesting that premature bi rth can lead to neonatal mortality. None of the control neonates died. The patterns of secretion of prolactin, prostaglandin F-2 alpha-metab olite (PGFM), and progesterone of control and treated animals around t he time of birth were similar. A transient pulse of PGFM was coinciden t with birth while prolactin levels in plasma increased before, and pr ogesterone concentrations fell steeply immediately after, parturition in both groups of animals. The only difference between control and tre ated animals was in the timing of the hormonal events, which, along wi th birth, was significantly advanced by the treatment. We conclude tha t cortisol may play a role in triggering parturition in this marsupial species.