NOVEL APPROACH TO INTEGRATIVE RENAL FUNCTIONAL CHARACTERISTICS IN VARIOUS TYPES OF DIURESIS

Abstract

The elaboration of a method and evaluation of the influence of changes in the function of nephron on the final phase of urine formation in collecting ducts is of great theoretical and practical importance. In experiments performed in female Wistar rats the features of urine formation in water diuresis were studied (peroral water load of 5 ml/100 g body weight), in saluresis (furosemide 1.0 mg/100 g body weight i/m, 1-deamino-arginine vasotocin (1d-AVT) 0.05 μg/100 g body weight i/m), and in osmotic diuresis (i/v 0.75 ml/100 g body weight of 40% polyethylene glycol-400 (PEG) solution). Urine and blood serum osmolality was determined by cryoscopic method, Na⁺ and K⁺ concentration – by flame photometry, Mg²⁺ and Ca²⁺ concentration – by atomic absorption spectrometry. In all cases, except ones with water diuresis, polyuria was caused by increased excretion of osmotic-active substances and was accompanied by a rise of reabsorption of free water after PEG and 1d-AVT administration. Calculation of the ratio of the solute-free water clearance (T^c_H2O) and osmotic clearance (C_Osm) has revealed the similarity of values following 1d-AVT and PEG administration (0.55±0.09 and 0.49±0.09, respectively), in contrast to furosemide injection (-0.03±0.04) that decreased free water reabsorption. The data obtained show that in saluresis and osmotic diuresis the volume of the reabsorbed free water depends on the rate of the fluid flow into the collecting duct against a background of high osmotic permeability of its wall. On the contrary, furosemide reduces osmotic permeability and free water reabsorption. Thus, characteristics of renal function in various forms of diuresis and the use of new approach in calculation of T^c_H2O/C_Osm allow to provide complete conception of the processes in renal medulla depending on the state of the system of urine osmotic concentration.