Compensatory adaptation of structure and function following progressive renal ablation

[Bilateral renal hypoplasia with oligomeganephronie. A morphometric, light- and electronmicroscopic study (author's transl)]

Kidney biopsy specimens of three patients with a special form of hypoplasia, the oligomeganephronic hypoplasia (Oligomeganephronie) were studied with light- and electron-microscopy as well as morphometric methods. The morphometric measurements demonstrated that there were no quantitative differences of the glomerular components between normal and oligomeganephronic glomeruli of patients of the same age. All of the structures measured--glomerular capillary surface, glomerular volume, volume of the glomerular capillary lumina and volume of Bowman's capsular space--were increased about 5.4 times. The volume of the proximal and distal tubules per mum tubular length in oligomeganephronic patients was disproportionally increased. The total number of glomeruli was more diminuished than mentionned in the literature until this time. The secondary glomerular sclerosis, initially focal, was progressive and supposed to be caused by "chronic overwork".

Age-dependent characteristics of compensatory renal growth

The age-dependent characteristics of compensatory renal growth were studied in neonatal, weanling and young adult rats. Compensatory growth was demonstrated to be greater in young, sexually immature animals than in adults following unilateral nephrectomy. In the four-week interval following surgery in 21-day-old weanling rats, renal mass increased 240% in control animals (group A) and 407% after unilateral nephrectomy (group B). In similarly prepared adult animals, renal weight increased 31 and 81% in the same groups, respectively. The remarkable response in compensatory growth achieved by the young animal was further demonstrated by a greater absolute increase in renal mass in the experimental kidney of young rats compared to adults. Further studies were performed to determine whether the mechanism of compensatory growth in young rats involved formation of new nephrons. The total glomerular count in the remaining kidney of rats after removal of one kidney at 5 (neonatal) and 21 (weanling) days of life did not differ from the value obtained in control neonatal, weanling or adult kidneys. These data indicate that compensatory renal hypertrophy is age-dependent and is greater in young animals. The mechanism for enhanced compensatory renal growth in young animals does not involve glomerular neogenesis since there was no evidence for formation of additional nephrons following nephrectomy either in weanling or neonatal animals.

Functional and hemodynamic adaptation to progressive renal ablation

Removal of renal tissue stimulates functional and anatomical adaptation in the remaining renal parenchyma. Since recent studies have demonstrated no apparent limitation in compensatory growth following progressive surgical ablation, experiments were performed to determine the changes in glomerular filtration rate and renal blood flow. After removal of 50% of the renal mass mean nephron glomerular filtration rate increased 60%, and after ablation of 75% of the renal tissue it increased 150%. These changes paralleled the increases in renal growth under the same conditions. In comparison, mean glomerular blood flow rose 90% and 240% after 50% and 75% nephrectomy, respectively; these changes in relation to the changes in glomerular filtration rate resulted in a progressive fall in the filtration fraction. Intrarenal blood flow distribution was examined with labeled microspheres. The marked increase in renal blood flow after surgical ablation was characterized by a disproportionate rise in blood flow to the inner cortex. The present investigation, therefore, described the remarkable functional changes that occur as overall glomerular filtration rate declines and provides further insight into the mechanism responsible for maintaining water and electrolyte homeostasis after loss of functioning renal mass.