Parturition in goats: studies on the interactions between the foetus, placenta, prostaglandin F and progesterone before parturition, at term or at parturition induced prematurely by corticotrophin infusion of the foetus.

Relationships between foetal corticosteroid concentrations, utero-ovarian prostaglandin F (PGF) and maternal peripheral progesterone have been examined in detail in goats shortly before spontaneous parturition at term. Foetal corticosteroids increased during the last 13-11 days of gestation and particularly sharply during the last 3 days and even during advanced labour. About 24 h before parturition, acute releases of PGF were evident in the vein draining the pregnant uterine horn, and these corresponded closely to the time of luteal regression. Further release of PGF occured when progesterone declined to low levels, probably reflecting in the course of labour. The changes observed before premature parturition, induced by infusing ACTH into foetal goats, were similar except for the more rapid increase in foetal corticosteoid concentrations. Immature neonates born after ACTH treatment were viable, placental delivery was normal and lactogenesis occurred in the mothers indicating that the treatment promoted full expression of the critical perinatal events. The early, acute releases of PGF were ipsilateral to the ACTH-infused foetus and were luteolytic provided the corpora lutea were also on that side. Luteolysis failed or was abnormally delayed if the corpora lutea were contralateral and prolonged ACTH treatment of the foetuses in such cases caused foetal death probably because of premature failure of the placenta. Similar findings were noted if ACTH infusion of the foetus was accompanied by simultaneous progesterone treatment of the mothers in order block the induction of labour. It was suggested that placental changes occurring during foetal hypercortisolism might be caused by increased placental oestrogen synthesis and the effect of this on the foeto-maternal junction along with a stimulatory action on PG synthesis in the maternal placenta. Experimental disruption of the normal sequence of events, when labour was blocked by progesterone, proved to be lethal to the foetus if the loss of placental integrity progressed sufficiently. The chain of regulatory signals linking increased activity of the foetal adrenal with parturition thus appears to involve stimulation of oestrogen biosynthesis, PGF release from the maternal placenta and the start of physical changes at the placental junction. Provided the foetus and corpora lutea are ipsilateral, the early releases of PGF effect luteolysis and a withdrawal of progesterone from the maternal circulation. When progesterone concentrations are sufficiently low, labour is initiated and its progress reflected by further release of PGF. The control mechanisms, which also provide for the final maturation of the foetus, clearly enable a close synchronization of the various perinatal events which are essential for the transition from foetal to postnatal life.