EXPERIMENTAL PARTIAL URETERAL OBSTRUCTION IN NEWBORN RATS - X - RENAL-FUNCTION AND MORPHOLOGY AFTER UNOBSTRUCTION

Partial obstruction of the left ureter was created in newborn rats. Un obstruction was performed after 2 or 7 days. The investigations were c arried out at 9 weeks of age - under slight hydropenia to institute an element of stress. Unobstruction was successful. On the unobstructed side, there were nevertheless impairments as compared to controls: uri ne osmolality (-32%), free water reabsorption (-44%), potassium excret ion (-34%), renal blood flow (-36%) and glomerular filtration (-36%). On the intact contralateral side, tubular changes were the only signs of an attempt to compensate. Thus, consistent renal damage remained de spite a very early unobstruction. Furthermore, the changes were simila r to those we observed during long-term permanent obstruction. The inj ury seems to be established within a very short time and imitates the probable development seen in the affected fetus: after start of produc tion, the urine is confronted by the preformed obstruction at the pyel oureteral junction. A high-pressure-prone system is built up and is no t reversed, until the pelvis has become dilated and thus capable to bu ffer urinary flow peaks. Thereafter, no further deterioration occurs e xcept in specific conditions. If clinically applicable, these observat ions implicate that there is no advantage with surgical intervention, even when performed early in fetal life, and there is no need for Swif t intervention, as the damage does not progress after its establishmen t. Most of the cases probably do not require surgery at all, unless pa in, obvious functional impairment or urinary tract infection supervene .