URINARY FLOW AND EXCRETION OF SOLUTES DURING OSMOTIC DIURESIS IN HYDROPENIC MAN

Abstract

The pattern of concn. and flow of urine during osmotic diuresis in dehydrated man was studied. Glucose, sucrose, mannitol, sorbitol, sorbose, xylose, urea, creatinine, Na para-amino-hippurate, Na sulfate, and NaCl were employed. A definite relationship between urinary flow or concn. and load was found independent of the ionic or chemical character of the solutes, or of the mode of their renal excretion. The assumption that the rate of decrease of the urinary concn. is proportional to the concn. and that the urinary concn. cannot fall below that of plasma, leads to an exponential equation: concn. = A''e(-k load)+ B where A[image] is a constant defining the urinary concn. at zero load, B is the total osmolarity of plasma, and k is a proportionality factor. A related expression may be derived for urinary flow. On the basis of these data and on the assumption of an isotonic absorption of solutes and water in the proximal tubule an equation for water reabsorption is proposed. Total water reabsorbed = Rpr + Rd = (GFR - load/B) +(load/B -load/A''e(-k load)+B), where Rpr and Rd are the amts. of water reabsorbed in the proximal and distal portions of the tubules, respectively, B is the total osmolarity of the plasma and GFR is the glomerular filtration rate.