Isolation and biosynthesis of 18-hydroxyprostaglandins E1 and E2 in human seminal fluid

18-Hydroxy-PGE₁ and 18-hydroxy-PGE₂ were identified in human seminal fluid by capillary gas-liquid chromatography-mass spectrometry. The levels of these prostaglandins was 1–2% of the corresponding 19-hydroxy-PGE compounds in human semen. 18Hydroxy-PGE₁ and 18-hydroxy-PGE₂ are likely formed by cytochrome P-450 in seminal vesicles in analogy with the 19-hydroxy-PGE compounds. This was supported by the finding that microsome of seminal vesicles of the cynomolgus monkey, Macaca fascicularis, supplemented with 1 nM NADPH, metabolized PGE₁ to both 19-hydroxy-PGE₁ (92%) and 18-hydroxy-PGE₁ (8%). The hydroxylation of prostaglandins in seminal vesicles of primates may thus show a high but not absolute specificity for the penultimate carbon of prostaglandins.