Capillary Permeability in Skeletal Muscle during Rest and Activity

In exercising skeletal muscle fluid is filtered from the blood stream to the interstitial space. The filtration process is facilitated by an increase of the capillary filtration coefficient. This coefficient is dependent upon capillary surface area and capillary permeability. The present study was designed to ascertain whether the capillary permeability increases in exercising muscle. The permeability of the capillary membrane was studied in two dogs. Dextran of different molecular sizes was injected intravenously, after which the concentration of the dextran in pure muscle lymph was compared with that in arterial plasma. The ratio between these concentrations did not change significantly when exercise was simulated by repeated stimulation of the motor nerve. It is therefore concluded that capillary permeability does not change during muscular exercise.