[Structural aspects of the decrease in several renal functions in old rats].

The proliferation, size and ultrastructure of the renal cells was studied in 32-38-month-old rats. At this age no dividing epithelial cells were found and their size was enlarged (in proximal areas of the nephrons by 30,2%, in the collecting tubes by 22%). The decreased rate of glomerular filtration in aged rats in dependent on the disturbance of hemodynamics in the glomerular capillaries, for which, to certain extent, the hypofunction of the rhenin-secreting complex is responsible. The reduction of microvilli, hypoplasia of the basal folds, changes in the orientation and size of the mitochondria are considered to be the structural basis of the decreased reabsorbtion in the proximal part of the nephron. In the distal part of the nephron the organization of the plasmalemmal-mitochondrial sodium pump is disturbed. In the collecting tube the number of dark cells becomes less, they shrink and disintegrate, which is considered to be responsible for disorders in the function of the hydrogen ions secretion. The decreased level of the physiological regeneration of cells is likely to underlie the disorders in renal functions in aged rats. The lack of proliferation gradually results in a deficiency of epithelial cells, their hypertrophy, functional stress and wear.