Microscopic Measurements of Local Capillary Permeability of Macromolecules in the Rabbit Skeletal Muscle

To clarify the mechanisms of transcapillary exchange of macromolecules, we tried to establish a new method for measurement of the local capillary permeability which can be obtained the diffusion (D) and convection (V) components separately. The anesthetized rabbit tenuissimus muscle was used to observe the micro-circulation and to measure the capillary permeability. After the injection of the fluorescent tracer (FITC-Albumin: FA67; M.W. = 67,000, FITC-Dextran: FD150; M.W.= 150,000 and FD500; M.W. = 500,000) via the jugular vein, temporal changes in the tracer concentration within the muscle tissue space were recorded as the fluorescent intensity changes by vital microscopic-TV system. D and V values were calculated by best-fitting the experimental concentration curve with the simulation curve based on the “Pore theory” in which macromolecules are assumed to pass across the capillary wall through the “Large pore” by diffusive and convective forces. Capillary permeability of diffusion component (Pdif) was calculated from D value as where Xw is the diffusion distance (length of pore). All animal experiments were carried out to keep the muscle under vasodilation topically. Obtained Pdif and V values of FA 67, FD 150 and FD 500 were Pdif=26.6±15.6, F=76.6±5.0, Pdif=3.3±0.8, F=45.0±5.0 and Pdif=2.1±l.l, F=47.0±9.0 (xlQ-Ws), respectively, which were largely consistent with the values reported by whole organ measurements. It was concluded that present method is useful to measure the local capillary permeability of macromolecules separated between diffusion and convection components.