Identification and quantification of prostaglandin E3 in renal medullary tissue of three strains of rats fed fish oil

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Abstract
Three strains of rats were fed a fish oil diet to verify their ability to incorporate and convert dietary eicosapentaenoic acid (20:5.omega.3) into trienoic prostaglandins. Such conversion indeed occurs in kidney medullae homogenates. The presence of prostaglandin[PG]E3 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 PGE3. Further evidence was provided by studying the recovery of exogenously added PGE3. 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 PGB3 for GC-MS analysis. The PGE3 was quantified by selected ion monitoring (SIM) with [3,3,4,4-2H4]PGE2 as internal standard. The levels of PGE3 were similar, .apprx. 3 ng/mg wet tissue, in the 3 strains of rats. Identical in vivo conversion of the 20:5.omega.3 fatty acid to PGE3 could not be positively established by analysis of pooled urine specimens.