Prostaglandins in the foetal pig and prepartum endocrine changes in mother and foetus

Chronically catheterized sows and their foetuses were used to investigate the changes in steroids and prostaglandins in maternal and foetal plasma and in allantoic fluid before and during parturition. A rise in foetal plasma corticosteroid concentration began 5-7 days before delivery. This was accompanied by a rise in oestrogen levels in foetal and maternal plasma and in allantoic fluid. There were a significant venous-arterial differences in oestrogen across both uterine and umbilical circulations. A more gradual decrease in maternal plasma progesterone levels occurred with a pronounced fall 24 hr before parturition; wide arterio-venous (uterine) and venous-arterial (umbilical) progesterone differences were found. Prostaglandin concentrations remained low in the maternal circulation until the day of farrowing, when PGF and its metabolic 13, 14-dihydro-15-oxo prostaglandin (PGFM) rose 10-20 fold. Foetal plasma levels of PGF, PGF and PGFM were higher than those of the sow in the prepartum period, while allantoic fluid concentrations were even greater. A delivery, PGE and PGF in the umbilical vein and allantoic fluid were raised but in the arterial plasma of the piglets at birth only PGFM levels were high. There was a close correlation between the neonatal PGFM levels and those in maternal arterial plasma at the time of delivery