Retained levels of dietary α-, γ- and δ-tocopherol in tissues and body fluids of Atlantic salmon, Salmo salar , L.

The purpose of this study was to describe the relationship between dietary supplementation and concentration of γ- and δ-tocopherol (TOH) in tissues of Atlantic salmon, Salmo salar, L., when α-TOH was fed at a constant level. Post-smolt Atlantic salmon (230 g) in duplicate tanks were fed a fish-meal-based diet with 250 g kg−1 lipid. Different combinations of RRR-tocopherylacetate preparations were added to give the following levels of TOH (mg kg−1) in diets 1–4, respectively: 150α; 150α+ 100δ; 150α+ 50γ+ 50δ; 150α+ 100γ+ 100δ. The concentrations of γ- and δ-TOH in most tissues were directly proportional to the feed concentrations. Exceptions were γ-TOH in erythrocytes, spleen and kidney and δ-TOH in heart muscle, where the intercept with the y-axis was significantly different from zero. The relative retained levels of α-, γ- and δ-TOH in most tissues were similar to their biological activities in mammals. An exception was muscle and adipose tissue, where γ- and δ-TOH were retained at rates of 70–90% and 20–35% compared with α-TOH, respectively. α-TOH was retained to a greater extent when α-TOH was fed alone than when γ- and δ-TOH were added to the diet. Fish growth was significantly correlated to total dietary TOH concentration. The data suggest that turnover of tocopherols in Atlantic salmon is similar to that in mammals, i.e. that discrimination between the tocopherols is mediated through competition for a tocopherol-binding protein in the liver, and consequently that α-TOH is preferentially secreted in very low density lipoprotein. Muscle and adipose tissue appear to be supplied with tocopherols from chylomicrons that have not yet been exposed to the hepatic discrimination mechanism.