Age-related changes in very low density lipoprotein metabolism in normal rats.

Plasma triglyceride (TG) concentrations rise with age, and we have carried out studies of very low density lipoprotein (VLDL) kinetics in the rat in an effort to define the cause of this phenomenon. Efficiency of VLDL-TG secretion by perfused rat liver decreases at rats age from 1 1/2-12 mo. However, this is compensated for by an increase in liver weight, and VLDL-TG secretion per perfused liver does not change with age. In contrast, total VLDL-TG secretion by the interact rat increases significantly as rats grow from 1 1/2-12 mo of age, and this increase is proportionate to the age-related increase in liver weight. The ability of the older rat to maintain VLDL-TG secretion proportionate to liver weight is most likely due to the concomitant rise in plasma free fatty acid concentration that occurs with age. However, the efficiency with which VLDL-TG is removed from plasma is not maintained as rats age. Consequently, the age-related rise in plasma TG concentration is due to an increase in VLDL-TG secretion proportionate to secretory mass, accompanied by a relative decline in efficiency of VLDL-TG removal from plasma.