Separation of prostaglandin E1 from its major metabolites: Application of the technique to measure first-pass clearance of PGE1 in the pulmonary and cerebral circulations of the anesthetized dog

A technique for the separation of prostaglandin E₁ (PGE₁) metabolites from parent PGE₁ in large numbers of plasma samples is described. Radiolabeled metabolites were enzymatically synthesized from [³H]PGE₁, using either the 100,000g supernatant fraction from rabbit lung homogenate or perfused dog lung, and purified by thin-layer chromatography. Separation of pure 15-keto[³H]PGE_i, 13,14-dihydro-15-keto[³H]PGE₁ and 13,14-dihydro[³H]PGE₁ from parent [³H]PGE₁ was achieved on microcolumns of silica gel. All three metabolites were completely eluted from the column with 10 ml of 0.1% formic acid in ethyl acetate. Less than 5 per cent of applied [³H]PGE₁ appeared in the metabolite fraction. [³H]PGE₁ was subsequently eluted from the column with 1% formic acid in ethyl acetate. Identical results were obtained with radiolabeled metabolites and parent PGE₁ extracted from dog blood. Application of this method to indicator-dilution experiments designed to measure removal of [³H]PGE₁ in dog lung and brain is reported. Pulmonary extraction and metabolism of [³H]PGE₁ at the peak of indicator-dilution outflow curves were 84.1 ± 2.2 and 41.8 ± 9.3 per cent (mean ± S.D., N = 20) respectively. Brain extraction from duplicate runs in one animal averaged 22 per cent with less than 5 per cent metabolism of [³H]PGE₁. These estimates agree well with previously reported data and thereby support the reliability and usefulness of this new method.