Experimental Obstructive Hydronephrosis in Newborn Rats

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Abstract
Partial obstruction of one ureter was created in newborn rats. The weights and blood flows (using the 86Rb-extraction method) of the cortex and outer and inner medulla were examined nine weeks later, i.e., in the adult. The obstructed pelvis was found to be enlarged 7-fold. The whole kidney blood flow on the hydronephrotic side was reduced by 10%; this was compensated by an increase on the contralateral side. There was a tendency to redistribution of flow from the cortex to the outer medulla; no other effects on regional flow were observed. The weight of the hydronephrotic kidneys was the same as that of the kidneys in control rats; hence no apparent atrophy was present. In contrast, the contralateral intact kidney was hypertrophied. The weight distribution of the different regions remained unaltered. Thus, the inner medullary weight was unaffected also on the obstructed side, although it showed considerable deformation. In the discussion, it is proposed that atrophy of the hydronephrotic kidney was probably present, but it was not detected because of the biological variation and the small number of observations. This presumed atrophy was uniform in all the regions and parallel with the reduction of whole kidney blood flow; hence the regional flows were relatively unaffected. It is concluded that unilateral partial obstruction in the newborn rat causes (i) discrete, parallel reductions of hydronephrotic kidney weight and flow, which are (ii) unrelated to the size of the obstructed pelvis and (iii) completely compensated by increases in the contralateral intact kidney.