Highly sensitive and specific RIA procedures have been used to measure
prostaglandin concentrations in the peripheral circulation of late pregnant and parturient women. The concentrations of
prostaglandin E (
PGE) and
prostaglandin F (
PGF) in plasma samples assayed within 4 weeks of collection were not significantly different among the groups studied, the levels (mean +/- SEM, picograms per ml) were: late pregnancy (n = 13):
PGE, 4.8 +/- 1.0;
PGF, 6.2 +/- 0.5; early term labor (n = 5):
PGE, 6.8 +/- 1.5;
PGF, 7.9 +/- 0.7; late term labor (n = 5):
PGE, 5.4 +/- 2.2;
PGF, 12.4 +/- 3.5; and
preterm labor (n = 7):
PGE, 4.4 +/- 0.4;
PGF, 6.9 +/- 1.4. The concentration of 13,14-dihydro-15-keto-prostaglandin F (
PGFM) in late pregnancy was 59.0 +/- 7.8 pg/ml. During spontaneous term labor, the concentration of
PGFM was significantly elevated (P less than 0.01) to 142.8 +/- 32.3 pg/ml in early labor and 282.7 +/- 55.3 pg/ml in late labor. The concentration of
PGFM in plasma from patients in
preterm labor (62.7 +/- 17.4 pg/ml) was not significantly different from that found during late pregnancy, but was significantly lower than levels found at term during early labor (P less than 0.05). The concentration of
PGE increased significantly in frozen plasma samples stored for more than 4 weeks in all groups studied; the concentration of
PGF was significantly elevated after storage only in the late pregnancy group (P less than 0.01). The plasma concentration of
PGFM in all groups studied was unaffected by storage. It is concluded that measurement of
PGFM concentrations is the most reliable method available of monitoring
prostaglandins in the peripheral circulation and that great care must be exercised in the assay and interpretation of
prostaglandin levels in human plasma.