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Influence of the renal cortical interstitium on the serum creatinine concentration and serum creatinine clearance in different chronic sclerosing interstitial nephritides.

54 biopsy cylinders of patients with different chronic sclerosing interstitial nephritides were investigated morphometrically. The point-counting method was used to determine the relative interstitial volume of the renal cortex. In this study, as in earlier investigations on inflammatory and noninflammatory glomerular diseases, as well as in studies on benign nephrosclerosis, significant positive correlations could be found between serum creatinine concentration and enlargement of the interstitium induced by fibrosis. Furthermore, correlations between decreasing serum creatinine clearance and fibrosis-induced interstitial broadening could be established. Enlargement of the interstitium by lymphocytic and plasma cellular infiltrates had no influence on renal function. Only in 1 patient were the findings not congruent with the above-mentioned observations. This could be explained by a severe anorexia nervosa with muscular atrophy and lack of available creatinine. The clearance values, however, showed the expected impairment of renal function. Interstitial fibrosis may lead to a narrowing of the postglomerular vessel network and to an elevated postglomerular flow resistance. In spite of increased glomerular filtration pressure, slowing of the glomerular blood flow could lead to an elevated serum creatinine concentration. A reduced glomerular filtration rate could lead to tubular atrophy as a sign of inactivity. Furthermore, the deficient Na-Cl resorption in atrophic tubules most likely perpetuates the decrease in the glomerular filtration rate. The glomerular filtration rate could be diminished by the so-called Thurau mechanism.