Influence of temperature and high dietary linoleic acid content on esterification, elongation, and desaturation of PUFA in Atlantic salmon hepatocytes.

The esterification, desaturation, and elongation of [1-14C]18:3n-3, [1-14C]18:2n-6, and [1-14C]20:5n-3 at 5 and at 12 degrees C were studied using cultivated hepatocytes from Atlantic salmon. The salmon were fed diets, in which 0, 50, or 100% of the supplementary fish oil had been replaced by soybean oil, for 950 day-degrees at 5 and 12 degrees C. The endogenous percentage of 18:2n-6 in hepatocyte lipids was 2% in cells from fish fed a diet with 100% of the supplemental lipid from fish oil, and it was slightly less than 25% in cells from fish fed the diet with 100% of the supplemental lipid from soybean oil. Furthermore, the percentages of 20:3n-6 and 20:4n-6 were significantly higher in hepatocytes from fish fed on soybean oil than they were in those of fish fed on fish oil. The percentages of 20:5n-3 and 22:6n-3, on the other hand, were lower. The endogenous levels of n-6 FA were not significantly correlated with the total amounts of radiolabeled FA esterified in hepatocyte lipids. The main radiolabeled products formed from 18:2n-6 were 20:2n-6 and 20:3n-6. The level of the important eicosanoid precursor 20:4n-6 was twice as high in hepatocyte phospholipids from fish fed the 100% soybean oil diet as it was in hepatocytes from fish fed the diet with 100% of supplemental lipid from fish oil. The main products formed from 18:3n-3 were 20:4n-3, 20:5n-3, and 22:6n-3. High levels of dietary 18:2n-6 do allow, or even seem to increase, the production of 22:6n-3 from 18:3n-3 in hepatocytes. The main products formed from 20:5n-3 were 22:5n-3 and 22:6n-3. The production of 22:6n-3 from 20:5n-3 was higher at 5 degrees C than at 12 degrees C. The percentage of 24:5n-3 was higher at 5 degrees C than it was at 12 degrees C, as was the ratio of 24:5 to 22:5. These results suggest that the elongation rate of 22:5n-3 to 24:5n-3 is higher at the lower temperature.

Infusion and sampling site effects on two-pool model estimates of leucine metabolism.

To assess the effect of site of isotope infusion on estimates of leucine metabolism infusions of alpha-[4,5-3H]ketoisocaproate (KIC) and [U-14C]leucine were made into the left or right ventricles of sheep and pigs. Blood was sampled from the opposite ventricle. In both species, left ventricular infusions resulted in significantly lower specific radioactivities (SA) of [14C]leucine and [3H]KIC. [14C]KIC SA was found to be insensitive to infusion and sampling sites. [14C]KIC was in addition found to be equal to the SA of [14C]leucine only during the left heart infusions. Therefore [14C]KIC SA was used as the only estimate for [14C]SA in the equations for the two-pool model. This model eliminated the influence of site of infusion and blood sampling on the estimates for leucine entry and reduced the impact on the estimates for proteolysis and oxidation. This two-pool model could not compensate for the underestimation of transamination reactions occurring during the traditional venous isotope infusion and arterial blood sampling.