EXTRAVASCULAR PROTEIN IN RENAL MEDULLA

The permeability to protein of the vessels of the renal medulla in the rat was studied by intravenous injection of Evans' Blue or fluorescent‐labelled serum, followed by perfusion of the whole vascular system with saline. The vessels of the inner medulla and the vasa recta of the vascular bundles of the outer medulla were found to be rapidly and freely permeable to protein. Electron microscopy, after the injection of ferritin, Thorotrast or colloidal gold, showed the vessels probably concerned in the protein leak to be ascending vasa recta and the capillaries of the medulla. The findings support suggestions that extravascular albumen is important in the process of concentration of the urine. © 1969 The Physiological Society