Interstitial fluid volume, colloid osmotic and hydrostatic pressures in rat skeletal muscle. Effect of venous stasis and muscle activity

Abstract

The effect of 24 h calval/iliac venous obstruction on interstitial fluid (IFV), hydrostatic (Pi) and colloid osmotic (COPi) pressure in hindlimb skeletal muscle was studied in 3 groups of rats: group I (G I).sbd.intact innervation, unrestricted motor activity; group II (G II).sbd.sympathectomized, unrestricted; and group III (G III).sbd.motor and sympathetic denervation + immobilization of hindlimbs. Subcutaneous edema was present in all groups at femoral venous pressure (Pv) exceeding 13 mmHg. Skeletal muscle edema was seen in G III at Pv > 12 mmHg, in 2 rats in G II at Pv of 18 and 23 mmHg, but in no rats in G I. Without venous obstruction, control COPi was 8-10 mmHg in all groups. With increasing Pv, COP fell moderately in G I and G II: .DELTA.COPi/.DELTA.Pv = 0.22. In G III, COPi fell from a control of 8.2 to 3.5 mmHg at a Pv of 12 mmHg (.DELTA.COPi/.DELTA.Pv = 0.52), but remained constant with further rise in Pv. Pi was about 0 mmHg in controls and 1-2 mmHg in rats with muscle edema. IFV rose by 6% per mmHg increase in Pv in G III, and 2% in G I and G II. This expansion of IFV may explain about 70% of the fall in COPi, the remaining being due to lymphatic washout of interstitial proteins. Normal muscle activity together with dilution and washout of interstitial proteins may constitute the main edema preventing mechanisms in skeletal muscle.