Most methods for data analysis were derived from the plasma radioactivity curve and were based on the general assumptions that synthesis and catabolism took place in a compartment in close contact with the intravascular space, that the study subjects were in steady state concerning IgG metabolism, and that metabolism of the labeled protein was identical with that of the native unlabeled protein (1). Figure 2a shows a semilogarithmic plot of the time-dependent decline of 125I-labeled IgG representing the disappearance of the tracer from the plasma in a normal subject. Graphical or mathematical methods allow estimations of the distribution in intra- and extravascular pools, of the.
