Stenosis of the tubular neck: a possible mechanism for progressive renal failure.

Fibrosis in chronic renal failure is closely associated with declining function. Its role in affecting function is less well defined. The radiation model of chronic renal failure was used to examine the tissue distribution of fibrosis and scarring and its role in influencing the loss of function in chronic renal disease. A striking and progressive pattern of fibrosis and narrowing of the glomerulotubular neck was found in irradiated pig kidneys. These narrowed necks increased in prevalence with time after irradiation. At 20 weeks after irradiation, the average neck diameter reduction was 60%, as compared with nonirradiated controls, a percentage that is consistent with a reduction in flow and pressure at this critical point of the nephron. Glomerulotubular neck narrowing may thus directly reduce the glomerular filtration rate of an individual nephron. Fibrotic neck stenoses may be a factor in progressive chronic renal failure.