PHYSIOLOGIC IMPORTANCE OF LYMPH 



1057 



phatic flow and composition produced by increased 

 venous pressure, we suggested that they might have 

 some bearing on the problem of plasma volume in- 

 crease and sodium retention in congestive heart fail- 

 ure, a syndrome in which venous pressures not infre- 

 quently approximate the high levels used in our 

 study. We pointed out that under conditions of signifi- 

 cantly increased venous pressure the total lymph flow 

 from both kidneys may amount to as much as 2400 ml 

 per 24 hours. This would represent a total of ±379 

 meq of sodium not excreted by the kidneys but re- 

 tained by the lymphatic system. A study of kidney 

 lymph flow in postural proteinuria might also be of 

 interest. Bull (32) believes that "A rise in pressure in 

 the inferior vena cava is produced by compression of 

 the vessel against the spine by the posterior surface of 

 the liver. This pressure is conducted back to the kid- 

 ney, inducing passive congestion and proteinuria. 

 The compression occurs when the subject is in a lor- 

 dotic posture and when the anterior surface of the 

 liver rotates inferiorly. This rotation of the liver 

 normally occurs when the subject is lordotic and is 

 maximal in the erect lordotic posture." Goodwin & 

 Kaufman (89) suggest the possibility of thoracic duct 

 or cisterna chyli lymphatic obstruction and retrograde 

 lymph flow as a possible explanation of the proteinuria 

 and cite the report of Lowgren (128) as suggesting this 

 explanation. 



If we agree that one of the primary functions of the 

 lymphatic system is to return to the vascular system 

 those proteins and other large molecules which have 

 leaked out of the blood capillaries, our accumulated 

 data emphasize that kidney lymphatics are no excep- 

 tion. This is a function of considerable importance for 

 the kidney. Maintenance of a relatively low concen- 

 tration of interstitial protein is necessary for the main- 

 tenance of the countercurrent action in the kidney. 

 This concept visualizes the vasa recta as a counter- 

 current exchanger carrying off salt and water. Gott- 

 schalk & Mylle (go) believe the efficiency of the coun- 

 tercurrent exchange in the vasa recta to be critical, 

 "for they probably remove not only the blood enter- 

 ing the medulla, but also the water that diffuses from 

 the thin descending limbs of the loops of Henle and 

 the collecting ducts. This water, with solute isosmotic 

 for the particular level of the medulla, presumably 

 moves into the vasa recta because of the gradient of 

 its chemical potential established by the colloid os- 

 motic pressure of the plasma proteins, since the hydro- 

 static pressure in the capillaries and interstitium are 

 the same." The gradient of colloid osmotic pressure 

 between the interstitium and the plasma can be main- 



tained only if the colloid osmotic pressure of the in- 

 terstitium is kept well below that of the plasma. We 

 believe that this is an important function of renal lym- 

 phatics, the maintenance of a relatively low oncotic 

 pressure in the interstitium and thus the establish- 

 ment of a gradient with the higher oncotic pressure 

 within the vasa recta. Thus, as the lymphatics carry 

 off plasma protein that has pooled in the medullary 

 interstitium, the colloid osmotic pressure of these pro- 

 teins draws water with a higher or lower solute con- 

 centration, depending upon the level of the counter- 

 current gradient at which the lymph is formed. The 

 medullary and cortical lymph passes into lymph col- 

 lecting trunks, mixing the two and thus reducing the 

 electrolyte concentration and osmolarity. Some col- 

 lecting trunks lease the kidney through the cortex 

 while others follow the path of the artery and vein to 

 the hilus. When renal venous pressure is increased, 

 more protein is lost in both cortex and medulla due to 

 increased hydrostatic pressure. Thus, although filtra- 

 tion of protein increases as does water, the concen- 

 tration of filtered electrolytes does not increase over 

 control values. We assume that filtered electrolvtes 

 from cortical capillaries are isosmotic with both 

 plasma and cortical interstitial tissue, while filtered 

 electrolytes from the vasa recta are hyperosmotic to 

 plasma but isosmotic to the countercurrent gradient 

 in which they lie. Thus, if these fluids are mixed, one 

 might expect the concentration of sodium in milli- 

 equivalents per liter to remain unchanged. This is es- 

 sentially what we find. 



In terms of the above discussion, we would expect 

 ligation or obstruction of lymphatic outflow to produce 

 edema and significantly alter kidney function. Kaiser- 

 ling & Soostmeyer (105) succeeded in tracing the 

 lymphatic vessels to the main hilar branch in rabbits 

 and in tying it off. The kidney began to swell immedi- 

 ately and had reached double its original size within 

 10 to 15 min as a result of massive interstitial edema. 

 There was a marked increase in urinary output on 

 the side with lymphatic ligation and, significantly, 

 the urine from the experimental side had a specific 

 gravity of 1 013, whereas the control side had a specific 

 activity of 1 035. Later, the urine flow diminished, 

 proteinuria was present, and the kidney and its 

 parenchymal cells degenerated 8 to 10 days after the 

 lymphatics were ligated. 



These and other similar studies and their implica- 

 tions are discussed at length by Babies (7, 8) and 

 Rusznyak et al. (189). 



Earlier mention was made of the fact that the first 

 experiments on renal lymph were those of Ludwig & 



