Plasma 6-keto-prostaglandin F1alpha: fact or fiction.

A radioimmunoassay for 6-keto-prostaglandin F1alpha was developed and validated. The apparent concentration of 6-keto-prostaglandin F1alpha in human venous plasma was found to be less than 50 pg/m1. A rise in plasma 6-keto-prostaglandin F1alpha was detected on infusion of prostacyclin or of DDAVP in human subjects. Various methods of organic extraction were applied to plasma samples prior to radioimmunoassay. Organic extraction and silicic acid chromatography introduced marked and unacceptable nonspecific interference on subsequent radioimmunoassay. This interference was abolished by high pressure liquid chromatography of eluates and extracts prior to assay. Using these methods, a very low concentration of 6-ketoprostaglandin F1alpha in human venous plasma was confirmed.