Modulation of very low-density lipoprotein secretion by dietary protein is age-dependent in rats

The Triton WR-1339 technique was used in order to study age-dependent changes of the rate of very low-density lipoprotein (VLDL) lipid secretion in rats consuming either casein or soy protein isolate. There was a significantly higher influx of lipoprotein cholesterol and triglycerides into the plasma compartment (of fasted animals) after a casein than after a soy diet, both in 10-week-old animals (cholesterol: 0.78 +/- 0.06 vs. 0.52 +/- 0.03 mmol X 1(-1) X h-1) and 25-week-old animals (cholesterol: 0.50 +/- 0.07 vs. 0.32 +/- 0.05 mmol X 1(-1) X h-1), but secretion rates diminished with age. The higher secretion rates following casein were paralleled by higher serum cholesterol levels in the fasted younger animals and also, though to a lesser degree, in the fed animals. These data contribute further evidence to our earlier proposal that dietary protein may induce different serum lipid levels by the modulating rate of lipid influx into the plasma compartment.