Effects of experimental obstructive hydronephrosis on the immature nephrons in newborn rats.

Partial obstruction of the left ureter was created in rats less than 36 h of age and its effects were studied at the age of 2-6 days. A considerable hydronephrosis with distension of the kidney developed within 1 day after obstruction, but there was no parenchymal weight reduction. The thickness of the mature, inner cortical layer was significantly decreased, suggesting a delay in the differentiation of the cortex. The parenchymal weight reduction, previously documented in our laboratory after long-standing ureteric obstruction, may thus be caused by a retardation of renal growth, which is never caught up, rather than by an atrophy of renal parenchyma or other destructive tissue lesions.