This study examined the effect of blocking proximal tubule lumens on glomerular and early proximal tubular morphology. Single nephrons in the rat kidney were blocked with wax by micropuncture. After one day, one week, or one month of obstruction, the kidneys were fixed with glutaraldehyde by intravascular perfusion, and nephron structure was examined by light and electron microscopy. Following obstruction, glomerular changes developed more slowly than tubular changes. After one day, the only change noted in some glomeruli was the presence of inflammatory cells. The only tubule change upstream to the block was a focal loss of apical microvilli. This is in contrast to the severe damage previously reported (Evan, Tanner: Kidney Int 30: 818-827, 1986) in downstream proximal tubule segments at this time. After one month of obstruction, glomerular size was decreased and the glomerular filtration membrane was abnormal. Tubular cell size was decreased, apical microvilli were lost, basolateral interdigitations were reduced, and mitochondria were fewer and abnormally oriented. Interstitial fibrosis was present. Changes in nephron structure develop slowly after obstruction, perhaps because continued filtration and reabsorption maintain nephron integrity. Eventually, blocked nephrons atrophy, probably because of reduced blood flow, disuse, and inflammatory responses.
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