Figure 1.

Multicompartment model of fluxes of FC. SAAM II model of cholesterol fluxes in and out of the plasma FC pool (V1), RBC FC (V2), plasma CE (V3), and rapid-exchange (mixing) pool in equilibrium with V1 (V4). k indicates rate constants 1/hour; s, sampling sites – data input into model; Infusion, site of constant infusion of FC. Parameters: R, infusion rate (mg/kg per hour); V1, plasma FC pool size (mg/kg body weight); V2, RBC FC pool size (mg/kg body weight); V3, plasma CE pool size (mg/kg body weight); k(0,1), rate constant for transfer of tracer out of plasma FC pool (hour⁻¹); k(0,3), rate constant for transfer of tracer out of plasma CE pool (hour⁻¹); k(3,1), rate constant for transfer of tracer from plasma FC to plasma CE pool (hour⁻¹); k(1,2), rate constant for transfer of tracer from RBC FC pool to plasma FC pool (hour⁻¹); k(2,1), rate constant for transfer of tracer from plasma FC pool to RBC pool (hour⁻¹); and s₁, s₂, and s₃ sampling sites, corresponding with V₁, V₂, and V₃. R, V₂, and V₃ entered as fixed parameters into the model; others are calculated by SAAM II. Steady-state equations: Flux 1=k(0,1)×V1=flux of plasma FC out of V1 (mg/kg per hour); Flux 2=k(2,1)×V1=k(1,2)×V2=exchange flux between plasma FC and RBC FC (mg/kg per hour); Flux 3=k(0,3)×V3=k(3,1)×V1=flux of plasma FC to plasma CE pool (mg/kg per hour); Flux 1+Flux 3=TCE (mg/kg per hour).