Very low levels of 6-keto-prostaglandin F1 alpha in human plasma.

Two stable derivatives of PGI2, its nonenzymatic hydrolysis product (6-keto-PGF1 alpha) and an enzymatic metabolite (6, 15-diketo-PGF1 alpha), were determined in human plasma and urine. These compounds were measured by RIA after separation on rp-HPLC. Previous purification of the samples on rp-HPLC markedly enhanced the specificity of the RIA determinations of those compounds in plasma and urine. The PGI2 derivative 6-keto-PGF1 alpha was detected in both plasma (4.7 +/- 3.2 pg/ml, mean +/- S.D., n=34) and urine (166 +/- 61 pg/ml, n=9). No gender differences of the plasma or urinary levels of 6-keto-PGF1 alpha were found. The PGI2 metabolite 6,15-diketo-PGF1 alpha was not measurable in plasma or urine (less than 1 and less than 10 pg/ml, respectively, n=4). Thus this compound may not be a major endogenous metabolite of PGI2 in man. When [3H]PGI2 was added to citrated blood immediately after venipuncture, it was recovered entirely as [3H]6-keto-PGF1 alpha after rp-HPLC. Therefore any circulating PGI2 would be measured as 6-keto-PGF1 alpha by our method. The results obtained suggest that PGI2 could be present in human venous blood under physiological conditions, but only in very low concentrations. (J Lab Clin Med 99:388, 1982.)