A sensitive radioimmunoassay for 11-deoxy-13, 14-dihydro-15-keto-11, 16-cyclo-prostaglandin E2: application as an index of prostaglandin E2 biosynthesis during human pregnancy and parturition.

A radioimmunoassay for 11-deoxy-13, 14-dihydro-15-keto-11, 16-cycloprostaglandin E2 (PGEM-II) is described. At pH 10.5, in the presence of albumin, 13, 14-dihydro-15-keto-prostaglandin E2 (PGEM-I) is transformed quantitatively into PGEM-II. Hence, after plasma samples are subjected to this transformation procedure, PGEM-II can be measured in such samples and be a true reflection of PGEM-I production and thereby prostaglandin E2 (PGE2) biosynthesis. The antiserum raised against PGEM-II is minimally cross-reactive with all prostaglandins tested (less than 0.01%). The mean least detectable mass of PGEM-II is 0.8 pg and the mean mass of added PGEM-II required to displace zero-point binding by 50% is 16.6 pg. The assay meets all the standard criteria for accuracy, reproducibility and parallelism. Concentrations of PGEM-II measured by this assay in peripheral plasma from men and nonpregnant women are similar to those reported for PGEM-I after measurements by gas chromatography - mass spectrometry. Plasma concentrations of PGEM-II in men were greater than in nonpregnant women. PGEM-II in increased concentration was found in early pregnancy although concentrations declined in the third trimester until labor when a significant increase was found. Concentrations of PGEM-II in umbilical venous plasma were significantly greater than those in maternal plasma.