DIETARY CONTROL OF THE RENAL REABSORPTION AND EXCRETION OF ALPHA-2U-GLOBULIN

The kidneys are an important factor in controlling the excretion of the sex-dependent protein, .alpha.2u globulin, in the urine. On a protein-free diet (0% casein), when the plasma level was reduced by 60%, the daily excretion of .alpha.2u in the urine was reduced from a normal of 11 mg to 0.2 mg; 97% of the .alpha.2u filtered by the kidneys was reabsorbed. When a normal-protein diet (20% casein) was restored, the serum .alpha.2u levels were returned to normal within 48 h. The urinary excretion remained below normal until the 8th day after repletion, whereas the renal concentrations of .alpha.2u reached higher than normal values by the 4th day. During protein deficiency the kidney reduced excessive losses of protein in the urine by an almost total reabsorption of .alpha.2u. On a high-protein diet (50% casein), the serum levels of .alpha.2u were normal, yet its excretion was elevated 80% above the normal (20 mg/day compared with 11 mg/day). To effect this increased loss, the reabsorption of the protein was reduced to 26% of the normal.