The effect of physiological levels of non-esterified fatty acids on the radioimmunoassay of prostaglandins.

Non-esterified fatty acids (NEFA) can significantly interfere with the radioimmunoassay of PGE and PGF2alpha using commercially available anti-sera. PGB1 antigen-antibody binding is 50% inhibited by 110 pg of PGB1, 48 ng of PGE1, 3.5 microgram of PGF2alpha, or 9.0 microgram linoleic, 14 microgram arachidonic, 22 microgram delta-linoleic, 40 microgram palmitoleic or 45 microgram oleic acids. PGF2alpha antigen-antibody binding is 50% inhibited by 270 pg of PGF2alpha, 70 ng of PGE1, or 4.2 microgram arachidonic, 14 microgram delta-linoleic, 22 microgram linoleic, 70 microgram palmitoleic or 110 microgram oleic acids. Physiological levels of NEFA, such as the quantities found in small volumes of plasma, are sufficient to prohibit accurate prostaglandin measurements. Chromatography on small columns of silicic acid proved to be an effective technique for separation of NEFA and prostaglandin from lipid extracts, however, the results of this study suggest that the interference produced by the presence of NEFA in the measurement of prostaglandin from certain physiological fluids may be avoided if the prostaglandins are not extracted prior to radioimmunoassay.