Relative contribution of triglyceride-rich lipoprotein particle size and number to plasma triglyceride concentration.

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Abstract
These studies were undertaken to determine whether differences in plasma triglyceride concentrations reflected differences in the number or in the size of the triglyceride-rich lipoprotein particles in the circulation. A population of 122 men and women, composed of normotriglyceridemic individuals and individuals with endogenous hypertriglyceridemia (plasma triglyceride concentration from 60 mg/dl to 1400 mg/dl), was studied by one of four independent experimental procedures. Rates of triglyceride production and particle (as reflected by apolipoprotein B) production were simultaneously determined. The data suggest that 71% of any increase in triglyceride production was due to an increase in the production of particles, and only 29% was due to an increase in the amount of triglyceride carried per particle. Direct measurement of the triglyceride-rich lipoprotein particle size by electron microscopy demonstrated that for a fivefold difference in triglyceride borne by the Sf 12-400 lipoproteins (from 100 mg to 500 mg triglyceride/dl plasma), the mean particle size rose by only 29%. Hence, 71% of this difference was due to an increase in particle number. The same results were obtained when triglyceride levels were related to the number of triglyceride-rich lipoproteins in the plasma. The number of particles for these studies was either estimated from apo B concentration or by calculations based on the chemical composition of ultracentrifugal subfractions. These studies have used four different approaches to show that changes of plasma triglyceride concentration primarily reflected a change in the number, not the size, of triglyceride-rich lipoprotein particles. Our studies also demonstrated that 75% to 80% of the triglyceride-rich lipoproteins in both normotriglyceridemic and hypertriglyceridemic subjects were in the Sf 12-60 or intermediate density lipoprotein subfraction.