Augmentation of Tissue‐Blood Transfer of Solutes by Transcapillary Filtration and Absorption

The effect of net transcapillary fluid movement on the rate of transfer of131I,24Na,86Rb and133Xe from tissue to blood was studied in cat skeletal muscle. The technique used permitted control, directly or indirectly, of other factors of importance for exchange, such as blood flow, flow velocity. capillary‐ flow distribution. size of capillary surface area and capillary permeability. Net fluid filtration was produced by raising mean hydrostatic capillary pressure and net fluid absorption by increasing plasma osmotic pressure. It was shown that a net transcapillary fluid movementper se(filtration or absorption) increased the transport rate from tissue to blood considerably above the control level when no net fluid movement occurred (Fig. 3). The rate of solute transfer seemed to increase progressively with the rate of net fluid movement, at least in the lower range. The extent to which transfer increased was roughly the same for all water‐soluble substances studied. While for133Xe net transcapillary filtration appeared to produce a less marked increase in transport rate. Reduction in nutritional blood flow was followed by a decrease in rate of isotope transfer. This decrease proved much smaller when the flow reduction was associated with net transcapillary fluid filtration. The possible physiological significance of transcapillary fluid movements for control of tissue‐blood exchange is tentatively discussed.