Supplements of evening primrose oil (Oenothera biennis), which contains at least 72% linoleic (18:2n−6) and 7% γ-linolenic (18:3 n−6) acids (expressed as % fatty acid methyl esters) were given to sixteen cystic fibrosis patients for a period of 12 months. Clinical observations showed no significant changes in patients' weights or respiratory function throughout. Linoleic acid levels in plasma and erythrocyte membranes increased significantly during the first 6 months but this increase was not sustained at its initial level. After supplementation was discontinued reversion to baseline (low) levels occurred within 4 months. Levels of plasma prostaglandins (PG) and urinary PG metabolites varied among individuals over a wide range, and urinary PGF2α metabolites fell during the supplementation. There was a significant fall in sweat sodium concentrations after 6 weeks of supplementation, but sweat chloride was unchanged. It is not known whether the effect of essential fatty acids on sweat Na+ reflects changes in cell membrane conformation or if there is a direct effect on Na+ pump activity.
