Aging in both humans and rats is associated with the development of insulin resistance and the ensuing alterations in the plasma lipoprotein profile. In this study, young (2 months) and old (15 months) Sprague-Dawley (SD) rats were used to investigate age-related alterations in the chylomicron clearance pathway. Clearance from the blood of an intravenously injected bolus of 14C-labeled cholesterol ester (CE) and 3H-labeled triacylglycerol (TAG) lymph chylomicrons was markedly delayed in the old rats (P < .05). Hepatic expression of the two principal receptors of chylomicron remnant removal, the low-density lipoprotein (LDL) receptor and LDL receptor-related protein (LRP), was determined by ligand blotting and immunoblotting. The old rats expressed 43%+/-7% of the level of LDL receptor in the young animals (P < .05) and 45%+/-16% of the corresponding level of LRP (P < .05). The results suggest that the delayed clearance of chylomicron remnants in this animal model of aging and insulin resistance is due, at least in part, to a decrease in the hepatic expression of LDL receptor and LRP.