Stereology of the rat kidney during compensatory renal hypertrophy

Different renal structures were studied during the initial phases of compensatory renal hypertrophy. Four days after unilateral nephrectomy, kidney weight had increased by 31%, total glomerular volume by 17%, and glomerular filtration surface by 10%. After 24 days, kidney weight had increased by 44%, glomerular volume by 24%, and filtration area by 22%. The proximal tubules increased their cell volume and diameter significantly after four days (30% and 11%), but tubular length did not increase until later. We conclude that during compensatory renal hypertrophy glomerular growth is less pronounced than tubular growth, and that the increase in filtration surface area is not sufficient to explain the increased glomerular filtration rate after nephrectomy. Proximal tubules initially grow transversally and only later on longitudinally, the two growth phases possibly corresponding to cellular hypertrophy and hyperplasia.