Identification and quantification of prostaglandin E 3 in renal medullary tissue of three strains of rats fed fish oil

Three strains of rats were fed a fish oil diet to verify their ability to incorporate and convert dietary eicosapentaenoic acid (20∶5ω3) into trienoic prostaglandins. Our results show that such conversion indeed occurs in kidney medullae homogenates. Specifically, the presence of prostaglandin E 3 (PGE 3 ) was established by gas chromatographic‐mass spectrometric (GC‐MS) analysis. That compound was conclusively identified by comparison of fragment ions and their relative intensities with those obtained from authentic PGE 3 . Further evidence was provided by studying the recovery of exogenously added PGE 3 . The crude ethyl acetate extracts of the medullary homogenates were methylated and cleaned up by liquid‐gel chromatography with Lipidex‐5000 prior to conversion to PGB 3 for GC‐MS analysis. The PGE 3 was quantified by selected ion monitoring (SIM) with [3,3,4,4‐ 2 H 4 PGE 2 as internal standard. The levels of PGE 3 were similar, about 3 ng/mg of wet tissue, in the 3 strains of rats. Identical in vivo conversion of the 20∶5ω3 fatty acid to PGE 3 could not be positively established by analysis of pooled urine specimens.