Protein concentration and hydrostatic pressure in subcutaneous tissue of rats in hypoproteinemia

Protein concentration and hydrostatic pressure were measured in subcutaneous tissue of rats during development of aminonucleoside nephrosis. Samples of interstitial fluid for protein analysis were collected from subcutaneous tissue by a wick method, and hydrostatic pressure was measured by a modified Scholander technique. When the serum protein concentration was reduced from 6.1 to 4.8 g/100 ml, interstitial fluid protein concentration fell from 3.0 to 1.1 g/100 ml. This corresponds to a reduction of calculated oncotic pressures from 18.0 to 13.0 mm Hg and from 7.8 to 3.0 mm Hg in serum and interstitial fluid, respectively, thus leaving a nearly constant net transcapillary oncotic pressure. When serum protein concentration was further reduced to 3.8 g/100 ml, interstitial fluid protein concentration was reduced to 0.5 g/100 ml, reducing net transcapillary oncotic pressure by 2-3 mm Hg. The average hydrostatic pressure in subcutis was 1.0 mm Hg subatmospheric under control conditions and did not change during hypoproteinemia. The results indicate that a reduction of interstitial protein concentration is an important factor in preventing edema formation in hypoproteinemia.