Chylomicron clearance in normal and hyperlipidemic man

A method has been developed for measurement of fractional clearance rates of chylomicrons in man. The technique employs constant infusion of emulsified fat into the duodenum at a rate of 200 mg/kg/hr. After 5 hr of infusion, concentrations of triglycerides (TG) in the chylomicron fraction become constant for the subsequent 5 hr. Since the input of chylomicron-TG is known, fractional removal rates can be calculated from steady-state plasma levels. In 21 patients with normal TG levels, clearance rates for chylomicrons were extremely rapid (t_1/2 for chylomicron-TG=4.5±2.9 (SD) min). In 30 patiemia, clearance was generally prolonged (t_1/2=23±5.5 min). This delay in chylomicron clearance could have been due either to a defect in removal of all TG-rich lipoproteins or to competition for removal between endogenous and exogenous particles; a generalized defect in clearance capacity for plasma TG was apparently ruled out for most patients by the further observation that reduction endogenous TG by caloric restriction caused chylomicron removal to return to normal. These studies also showed that endogenous-TG is removed much less efficiently than chylomicron-TG, and in some patients, this discrepancy is particularly marked.