DIET-INDUCED STRUCTURAL AND FUNCTIONAL MODIFICATIONS IN THE PIG-LIVER ENDOPLASMIC-RETICULUM MEMBRANE - EFFECT OF POLYUNSATURATED FATTY-ACID DEFICIENCY

Weaned 39-day-old female piglets were fed diets containing either com-soybean oil (control) or hydrogenated coconut oil (essential fatty acid (EFA) deficient) for 12 weeks. EFA deficiency produced increased cholesterol (Chol) and decreased phospholipid (PL) contents relative to protein, and thereafter an enhanced Chol/PL molar ratio in the liver endoplasmic reticulum (E.R.) membrane. The primary changes included modified PL distribution, with significant decrease in phosphatidylcholine (PC) and increase in phosphatidylinositol (PI) and phosphatidylserine (PS) levels. Furthermore, fatty acid profiles of the four main PL classes were altered by EFA deficiency. In particular, linoleic, arachidonic, and docosapentaenoic acid levels were largely reduced, whereas palmitoleic and oleic acid levels were increased. The biosynthesis of 5, 8, 11-eicosatrienoic acid (from oleic acid) was strongly stimulated in EFA-deficient pig liver E.R. membranes. The lower polyunsaturated fatty acid level of these latter induced a decreased peroxidability as measured by thiobarbituric assay. Moreover, the modified lipid composition due to EFA deficiency was followed by a decrease in membrane fluidity and an alteration in the activity of several membrane proteins. Liver E.R. membrane from EFA-deficient piglets exhibited a decreased Ca++ uptake, although passive Ca++ efflux was unaffected. NADH-Cyt.b5 and NADH-Cyt.b5 reductase activity were enhanced, whereas NADPH-Cyt. P450 electron transferring system and some of the liver detoxifying enzyme activities were significantly depressed.