Experimental Partial Ureteric Obstruction in Newborn Rats. VII. Are the Long Term Effects on Renal Morphology Avoided by Release of the Obstruction?

Abstract

Partial obstruction of the left ureter was created in newborn rats. The obstruction was either permanent or was released after two or seven days. The effects were studied at the age of six weeks. The permanently obstructed kidneys characteristically exhibited considerable enlargement (X 18) of pelvic volume and prominent deformation of the papilla, frequently associated with moderate widening of collecting ducts and convoluted tubuli, and focal inflammatory and degenerative lesions. The weight difference between the hydronephrotic and the contralateral, intact kidney was significantly higher than in a sham operated group, although the combined kidney weight was unchanged, indicating a reduction on the obstructed side and a compensatory contralateral hypertrophy. In the group released after seven days, the pelvic volume had returned to normal; nevertheless the parenchymal weight pattern and the histological lesions were similar to those found in animals obstructed for six weeks. In the group released after two days, the pelvic volume had normalized, and the histological changes were less prominent than in animals obstructed for seven days or six weeks. Yet there was a significant difference in parenchymal weight between the hydronephrotic and the contralateral kidney, almost entirely caused by hypertrophy on the nonobstructed side. Thus, the ureteric obstruction must be released very early to avoid parenchymal weight reduction and curb the tissue lesions. On the other hand, the resulting parenchymal damage is moderate and does not seem to progress with time.

Experimental Partial Ureteric Obstruction in Newborn Rats

“…Persistent microstructure lesions have been thought to be a source of stimulation [21], In the present series, we found mild, possibly nonspecific changes, simi lar to those previously reported as early as 1-6 weeks after release [12,13]; however, these seem too discreet to induce stimulation. Persistent /imc7/o« reduction is anoth er explanation.…”

“…In short, the contralateral kidney increased as regards kidney weight, renal blood flow and glomerular filtration, thereby fully compensating for the moderate reductions on the ipsilateral side. In parallel studies [12,13], the obstruction was released -after 2 or 7 days. 6 weeks later, hydronephrosis was never present.…”

Experimental Partial Ureteric Obstruction in Newborn Rats

“…In our studies concerning morphology, rats were obstructed at 1-2 days of age and unobstructed after 2 or 7 days [5,6,8]. When studied 6 weeks later, no signs of hydronephrosis remained.…”

“…It is unclear if these changes are avoidable or reversible by unobstruction, as this has only rarely been studied, and even more seldomly in immature animals with partial obstruction [5][6][7][8]. In our studies concerning morphology, rats were obstructed at 1-2 days of age and unobstructed after 2 or 7 days [5,6,8].…”

Effects of Experimental Obstructive Hydronephrosis on the Immature Nephrons in Newborn Rats

“…During the first 4-5 days, the glomeruli in the subcapsular layer are in the S stage [1], resembling the human fetal kidney in the last trimester [2], On the basis of autopsy studies in human fetuses, Osathanondh and Potter [3] postulated that immature nephrons are particulary susceptible to obstructive nephropathy. These authors found that par tial obstruction of the urethra caused dysplastic renal changes, whereas partial obstruction of the ureter was associated with but little renal change, possibly reflecting that, in the latter case, the obstruction is usually less severe and occurs at a later stage of fetal develop ment [4], Our own previous studies indicate that the influence of partial ureteric obstruction on the neonatal rat kidney is particularly evident during the first few days after birth [5,6], i.e. at a stage when the subcapsular nephrons are still immature [1].…”