Prostaglandins at parturition and in the neonatal infant.

In man, administration of prostaglandin E, or F, will stimulate labour and abortion (Embrey, 1971; Thiery, 1979), whereas administration of prostaglandin synthase inhibitors will delay delivery and suppress pre-term labour (Wiqvist, 1979). Measurements of prostaglandins E, and F,, in peripheral plasma are hampered by the low concentrations present (Samuelsson, 1973) due to rapid clearance by the lungs and also by the problem of prostaglandin production by platelets (Smith & Willis, 1970). A major metabolite of prostaglandin F,, is 13,14-dihydro15-oxoprostaglandin F,, (prostaglandin FM), which circulates in 10-30-fold higher concentrations, is not formed by platelets and hence is measured in peripheral plasma as a monitor of prostaglandin production (Samuelsson, 1973). Circulating concentrations of prostaglandin FM apparently increase slightly during late gestation, with a massive elevation occurring during labour (Green et al., 1974). Peripheral plasma concentrations of prostaglandins E, and F,, do not change significantly with labour (Mitchell et al., 1978d), suggesting that the lungs have the capacity to cope with the increased production of prostaglandins at