Fig. 4.

Schematic bar graphs showing the changes with time in precursor amino acid (P), incorporation rate into apolipoprotein (S), and amino acid (AA) in apolipoprotein (M) for two types of tracer studies. The full height of each bar represents the total of tracer and tracee, whereas the hatched portion is for the tracer. The subscript T stands for total (tracer plus tracee), L stands for tracer (label), C stands for constant infusion, B stands for bolus, and 1, 8, and 15 indicate 1, 8, and 15 h. The left panels are for a primed constant infusion. The upper left panel shows that the tracer in the precursor increases and stays at a constant fraction from 1 to 15 h. The middle left panel shows that apolipoprotein incorporation is unchanged, with the tracer contributing that same fraction from 1 to 15 h. The bottom left panel shows that the apolipoprotein mass remains the same while the amount of label increases from 0 to 1 to 8 h, approaching a plateau at 15 h. The right panels are for a bolus study. The upper right panel shows that the tracer in the precursor increases and then declines from 1 to 15 h. The middle right panel shows that the apolipoprotein incorporation is unchanged, with the tracer contributing a fraction equal to its fraction in the precursor. The bottom right panel shows that the apolipoprotein mass remains the same while the amount of label increases from 0 to 1 h and then decreases to 15 h.