A study by microdissection and micropuncture of the structure and the function of the kidneys and the nephrons of rats with chronic renal damage

A study by microdissection and micropuncture of the structure and function of the kidneys and nephrons of rats with chronic renal damage. Individual nephrons were studied by microdissection and micropuncture in rats three to four weeks after subcutaneous injection of K2Cr2O7 and HgCl2 for comparison with clearances and tubular transport maximums (Tms) that represented the total activity of the kidney from which they were obtained. At the time of the experiments the acute renal lesions of necrosis had been replaced by regenerative processes of repair. This model has no exact clinical analogy but the structural changes in individual nephrons are similar to those observed in nephrons of humans with chronic renal disease. The kidneys were irregularly and greatly enlarged; in histologic sections there were moderate glomerular and extensive tubular changes. Microdissection demonstrated the renal lesion to be a combination of regressive changes (atrophy, fatty depositions) in some proximal convolutions, progressive reactions (hyperplasia, hypertrophy) in others or more frequently a combination of these alterations in single structural segments (the proximal convolutions) of individual nephrons. Glomerular filtration rates (GFR) in the damaged kidneys ranged from the highest to less than the lowest of normal control values but were lower when calculated per gram of kidney weight. Since TmPAH was normal, TmPAH:GFR was increased, indicating functional tubular predominance, correlating closely with the evidence by microdissection of morphological tubular hyperplastic predominance in the abnormal kidney. There was marked heterogeneity of individual néphron GFR but proximal fractional reabsorption was the same as in control nephrons, indicating that rates of reabsorption were also more variable than normal but appropriate for the rate of filtration. Tubular fluid transit times were markedly more variable than in normal animals yet correlated closely with morphological changes demonstrated by microdissection in the same nephrons on which the determination had been made. Microinjection indicated that the repaired abnormal tubules were impermeable to inulin. These results demonstrate a close correlation between the heterogeneity of structure and function at the level of the individual nephrons and, therefore, in their totality as they constitute the kidneys of rats with chronic renal damage. Although the rates of physiological processes showed marked diversity, proximal f