Comparative analysis of the protein content of local subcutaneous tissue fluid and plasma

Abstract

Local subcutaneous tissue fluid from rabbits was sampled with a liquid paraffin cavity method. The albumin, globulin, and total protein content of the nanoliter samples of the fluid obtained by this method were determined by electrophoretic separation on cellulose acetate strips and polyacrylamide gels. The total protein, albumin, and globulin content was quantitated from microdensitometer scannings after different staining procedures. Plasma samples were treated identically and ran simultaneously. The average protein content of tissue fluid was 32% of the plasma protein content. The albumin:globulin ratio of tissue fluid, 2.67, was significantly higher than the corresponding plasma ratio of 1.64. Direct injury (local burn) increased the protein content of local tissue fluid and decreased the albumin:globulin ratio. The results imply that there is normally a marked difference between the extravasation of albumin and globulins to the interstitial fluid compartment. The effect of the sampling procedure and direct local injury (burn) on capillary permeability was also evaluated by determining the exchange of radioactively labeled albumin from plasma to the tissue fluid. Two and a half hours after the intravenous injection of the labeled protein, the tissue fluid activity was only 8% of that of plasma. The locally sampled subcutaneous tissue fluid thus has a low plasma protein content, a high albumin:globulin ratio, and the exchange rate of intravenously injected albumin to the fluid is low. The effect of the found tissue fluid protein content on interstitial colloidosmotic pressure is considered.