Maternal plasma prostaglandin E₂ metabolite levels during human pregnancy and parturition

Summary. Because of methodological problems associated with the measurement in biological fluids of both prostaglandin E₂ (PGE₂) and its unstable principal circulating metabolite 13,14‐dihydro‐15‐keto‐PGE₂ (PGEM), there is little reliable information on these prostaglandins in human pregnancy and parturition. The recent discovery of a stable PGEM degradation product 11‐deoxy‐13,14‐dihydro‐15‐keto‐11β, 16‐cyclo‐PGE₂ (bicyclo‐PGEM) has provided a means of studying endogenous plasma levels of PGEM which circumvents the problems encountered with direct measurements of PGE₂ and PGEM. Using a radioimmunoassay for bicyclo‐PGEM we have therefore determined maternal peripheral plasma PGE₂ metabolite levels during human gestation. PGE₂ metabolite levels did not alter significantly during the second or third trimesters nor during labour. This contrasts with maternal peripheral plasma levels of the principal circulating metabolite of PGF_2α 13,14‐dihydro‐15‐keto‐PGF_2α (PGFM) which increases several fold during labour. Compared t o PGE₂ therefore. PGF_2α may be quantitatively the more significant prostaglandin associated with human parturition.