Validation of an Incompletely Coupled Two-compartment Nonrecycling Catenary Model for Turnover of Liver and Plasma Triglyceride in Man.

Pool sizes and turnover rates of hepatic triglycerides and of lipids of three plasma lipoprotein fractions of human subjects were defined from studies of the rates of incorporation of labeled free glycerol and of labeled palmitate into these lipids, and of distribution and clearance from plasma of intact, endogenously labeled lipoproteins. Incorporation of labeled glycerol and labeled palmitate into plasma lipoproteins was prompt. Triglycerides of the lowest density lipoprotein class (S, > 20) were most highly labeled of all plasma lipoproteins, and turnover was most rapid in this class. The kinetic behavior of radioactive plasma triglyceride was more complex when palmitate was used than when glycerol served as a labeled precursor, probably because glycerol recycled less than did palmitate. An incompletely coupled, two-compartment, nonrecycling catenary (linked in series) model of hepatic triglyceride and of plasma Sf > 20 triglyceride was validated. The S, > 20 triglycerides turned over in a volume approximating that of plasma. Apparently unique to man of various species previously reported is the relatively slow turnover and consequent ratedetermining role of Sf > 20 triglyceride in this two-pool system. The hepatic pool greatly exceeded that in plasma and turned over approximately three times more rapidly.