Very low levels of 6-keto-prostaglandin F 1/sub α/ in human plasma

Two stable derivatives of PGI2, its nonenzymatic hydrolysis product (6-keto-PGF1/sub α/) and an enzymatic metabolite (6, 15-diketo-PGF1/sub α/) 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/sub α/ 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/sub α/ were found. The PGI2 metabolite 6, 15-diketo-PGF1/sub α/ was not measurable in plasma or urine (<1 and <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/sub α/ after rp-HPLC. Therefore any circulating PGI2 would be measured as 6-keto-PGF1/sub α/ 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