Proximal tubules in long-term compensatory renal growth. Quantitative light- and electron-microscopic analyses

The aim of this study was to determine the effects of long-term compensatory growth (CRG) on the dimensions and ultrastructure of the renal proximal tubules. CRG was induced in right kidneys of pigs by subjecting the contralateral (left) kidneys total ureteral obstruction for 10 weeks. The length density (Lv) of proximal tubules was assessed at the light-microscopical level. Peritubular and luminal diameters, volume density (Vv) of mitochondria and surface density (Sv) of basolateral cell membranes were determined on montages of electron micrographs representing entire tubular cross-sections. Kidneys with CRG showed an average increase in weight of approximately 36%. The proximal tubules had near normal cross-sectional dimensions, surface density of basolateral cell membranes and volume density of mitochondria. The length density of proximal tubules was also the same as in control kidneys. However, there was an estimated increase in total proximal tubular length of almost 45%. The present results, combined with observations from short-term studies of CRG, suggest that the proximal tubules undergo a series of structural changes initiated by hypertrophy of cells and organelles and resulting in a state of predominant hyperplasia.