Metabolism of triglyceride-rich emulsions in rats with protein malnutrition.

Knowledge of chylomicron metabolism is very important in understanding and treating protein malnutrition, since these particles are the primary carriers of dietary fat in lymph and plasma. In the bloodstream, fat transported in chylomicrons is hydrolyzed by the action of lipoprotein lipase and the resulting fatty acids and glycerol are taken up by the body tissues. Chylomicron remnants are then rapidly removed by the liver. To clarify chylomicron metabolism in protein malnutrition, triglyceride-rich emulsions known to behave metabolically like lymph chylomicrons and labeled with 14C-cholesteryl ester and 3H-triglycerides were injected intraarterially into control rats and rats fed a protein-deficient diet for 40 days. Plasma kinetics and organ uptakes of the labeled lipids were determined. Hydrolysis of the emulsion triglycerides by lipoprotein lipase was not different in the malnourished rats (TG-FCR = 0.250 +/- 0.027 m-1 vs 0.250 +/- 0.070 m-1 in controls), but plasma clearance of the resulting triglyceride-depleted emulsion remnant particles was markedly lower compared to controls (cholesteryl-ester FCR = 0.088 +/- 0.009 and 0.146 +/- 0.019 m-1, respectively, p < 0.001). These results were obtained regardless of the amount of emulsion lipid that was injected. Liver atrophy seem to account for the delayed remnant uptake in protein-depleted rats. These data provide insight into the consequences of parenteral nutrition with lipid emulsions when administered in states of protein malnutrition.