Fetal control of parturition in marsupials

Abstract

Among marsupials, the control of birth is best understood in the tammar wallaby. The young is tiny relative to the mother and is highly altricial. Adult female tammar wallabies weigh 5 kg, whereas the neonate weighs about 400 mg. However, despite this small size, there is clear evidence that the fetus provides the signal that sets the timing of birth through several mechanisms. A fetal signal activates a nitric oxide-guanylate cyclase system in the myometrium that may maintain myometrial inactivity, and this is down-regulated at term. There is also up-regulation of prostaglandin (PG) production in the gravid endometrium during the last two days of gestation that parallels increased placental..