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Correlations between the relative volume of the intertubular capillaries in the renal cortex and the serum creatinine concentration in primary glomerulopathies, renal vasculopathies, and chronic interstitial nephritides are reported. In the mesangioproliferative glomerulonephritides, there are significant negative correlations between the number and area of the intertubular capillaries in the cortex and the serum creatinine concentration. In diabetic glomerulosclerosis, renal glomerular amyloidosis, decompensated benign nephrosclerosis, secondary malignant nephrosclerosis, and chronic interstitial nephritis, there is a significant negative correlation between the relative area of the intertubular capillaries and the serum creatinine concentration. Thus, in these diseases, there is progressive narrowing/ obliteration of the postglomerular capillaries which leads to a progressive decrease in glomerular filtration rate and thus to a rise in serum creatinine concentration.

Summary.Our study in a group of patients (heterogeneous in terms of glomerular lesions), supplementing and confirming earlier findings, indicated that1. An increase of the relative cortical interstitial volume and the serum creatinine concentration at the time ob biopsy is accompanied by a statistically significant reduction in the number of intertubular capillaries and a decrease in capillary area per area unit.2. The length of diffusion between the intertubular capillaries and tubuli increases and the tubular epithelium becomes atrophic as relative cortical interstitial volume increases.3. The glomerular capillaries and the Bowman's capsule are significantly larger in moderately severe mesangioproliferative or grades I to III membranous GN with elevated serum creatinine concentrations than in equally severe renal diseases with normal serum creatinine concentrations.4. The glomerulus in moderately severe mesangioproliferative GN progressively increases as the serum creatinine concentration rises.On the basis of these findings, it was concluded that the increase of the cortical interstitial volume results in an increase in resistance of the postglomerular capillary network with impairment of the glomerular flow. This impairment leads to a functional or, to be more precise, a chronic rise in hydrostatic pressure and also to a reduction in the glomerular blood flow and therefore a rise in serum creatinine concentration. The chronic rise in hydrostatic pressure also results in an increase in the size of the glomerulus. The increase of the cortical interstitium additionally leads to an increase in the length of diffusion between the tubules and the intertubular and peritubular capil- laries. This increase in the length of diffusion subsequently results in atrophy of the tubules, reduction of reabsorption, and therefore impairment of the effective filtration pressure.

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