A sensitive radioimmunoassay for 6-keto-prostaglandin F1alpha: preliminary observations on circulating concentrations.

A radioimmunoassay for 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) is reported. The mean least detectable mass of 6-keto-PGF1alpha is 1.45 pg and the mean mass of added 6-keto-PGF1alpha required to displace zero-point binding by 50% is 94.2 pg. Cross-reactivities of the antiserum with all the prostaglandins and related compounds tested are less than 0.1% except for PGE2 and PGF2alpha which are respectively 0.16% and 0.80%. The assay is both accurate and reproducible and measured levels are in good agreement following extraction of 0.25--4.0 ml of plasma. Mean circulating concentrations of 6-keto-PGF1alpha in five non-pregnant humans, rhesus monkeys and sheep were 115, 65 and 25 pg/ml respectively.