Kinetic Analysis Using Specific Radioactivity Data

This chapter focuses on the kinetic analysis using specific radioactivity data. In kinetic turnover studies, a tracer amount of radiolabeled material is injected intravenously as a bolus. The biologic half-life and/or the in vivo metabolic fate of the material of interest can then be determined by analyzing the decay curve, which describes the disappearance of the injected. Available programs for compartmental analysis, however, are primarily designed for the analysis of total radioactivity (TR) data. Thus even if specific activity (SA) data are available experimentally, a common practice has been to multiply these SA data by an estimate of the appropriate pool size to obtain the TR data used in the analysis. This chapter defines a number of relationships characteristic only of SA data which can be used to derive information regarding the trace. The application of these relationships in the elucidation of pathways for the metabolism of apolipoproteins is illustrated for two systems: (1) the precursor–product relationship between very low-density lipoprotein (VLDL) and intermediate-density lipoprotein (IDL) apoB, and (2) the instantaneous equilibration of apoC-III in plasma. The chapter describes the relationship in equilibrating systems: metabolism of ApoC-III.