Extremely decreased release of prostaglandin E₂-like activity from chopped lung of ethyl linolenate-supplemented rats

Abstract

Three groups of weanling male rats were reared on a fat-free diet for 13 weeks. One group received only the fat-free diet (FF rats), the other 2 groups received the fat-free diet and a daily supplement of 2 energy% ethyl linoleate ([n−6] rats), or 2 energy% ethyl linolenate ([n−3] rats). The chopped lung preparation was used to illustrate an in vitro prostaglandin formation. PGE₂-like activity was quantified on rat stomach strip. The release of PGE₂-like activity expressed as ng PGE₂-equivalent per g lung tissue (mean±SD) was 23±7, <6, and 65±20 for the FF rats, the (n−3) rats, and the (n−6) rats, respectively. PGE₂ quantification by radioimmunoassay of the chopped lung effluent collected after passing over the rat stomach strip revealed the same release pattern as the bioassay. Fractionation of chopped lung effluent on HPLC with radioimmunoassay detection indicated that the lung tissue from (n−3) rats released very little PGE₃, if any, in spite of a 20∶5(n−3)/20∶4(n−6) ratio of 5.2 in the lipids of the lung. It is suggested that the pool of arachidonic acid for prostaglandin production in vitro is different from the one which functions in vivo, and that these pools are differently affected by dietary EFA.