QUANTITATIVE MORPHOLOGY OF RENAL CORTICAL STRUCTURES DURING COMPENSATORY HYPERTROPHY

The compensatory hypertrophy in different renal cortical structures wa s studied in rats 10 and 21 days after unilateral nephrectomy (UNX). Q uantitative morphological/stereological analysis revealed significant increases in total renal cortical volume - 33% on day 10 and 48% on da y 21 - after UNX. These changes were paralleled by significant increme nts in the volumes of proximal convoluted tubule (PCT, 55%), distal co nvoluted tubule (DCT, 114%), and cortical collecting duct (CCD, 106%) segments on day 10. The corresponding changes on day 21 were 76, 122, and 212%, respectively. These alterations were accompanied by increase s in segment length; 3% PCT, 23% DCT, and 50% CCD on day 10 and 9% PCT , 30% DCT, and 142% CCD on day 21 after UNX. The total luminal and bas olateral cell membrane surface areas also exhibited a time-dependent i ncrease after UNX. The increments in both luminal and basolateral memb rane domains in PCT and DCT after 10 days were not significant, but re ached significance after 21 days (PCT: luminal membrane 21%, basolater al membrane 63%; DCT: luminal membrane 98%, basolateral membrane 63%). In contrast, CCD membrane areas had increased substantially already 1 0 days after UNX (luminal membrane 92%, basolateral membrane 71%). It declined subsequently by day 21 (luminal membrane 57%, basolateral mem brane 32%). The cell rubidium concentration after a 30-second rubidium infusion, an index of Na-K-ATPase activity, as well as sodium concent rations were unaltered in cells of all nephron segments investigated. Altogether the stereological analysis shows that the compensatory incr ease in organ volume can be attributed primarily to an increase in nep hron epithelial volume. The PCT responds with 'radial' hypertrophy (th ickening of the tubular epithelial wall), while the DCT undergoes 'len gth' hypertrophy (increase of tubular length without thickening of the tubular wall and without an increase in number of cells). This type o f hypertrophy is especially prominent on day 21 after UNX for the CCD which doubles in length. Only on day 10 does the CCD seem to respond w ith hyperplasia. Adaptive changes in response to UNX develop gradually . Only a few of the morphological parameters studied had completed the ir change by 10 days, the majority required longer.