Fig. 2.
Schematic diagrams of the four pharmacodynamic models. The dashed arrows indicate links to the recombinant human erythropoietin (rHuEPO) central compartment of the pharmacokinelic model. The model operation and symbols are explained in the Methods section. τ = signal transduction transit time; EC50 = concentration of rHuEPO eliciting 50% of maximum signal; kin = maximal zero-order endogenous production rate constant of progenitor cells; N = number of compartments; P = precursor cell age compartment; R = reticulocyte compartment; SC50 = EPO serum concentration necessary to maintain the progenitor cell production rate at 50% of its maximum; SC50p = EPO serum concentration eliciting 50% of maximum stimulation of precursor cell maturation, Smax = maximum stimulation factor of precursor cell maturation; Tp = mean lifespan of precursor cells; TR = mean lifespan of circulating reticulocytes.