Hemodynamic Changes After Complete Unilateral Ureteral Obstruction in the Young Lamb

Obstructive nephropathy and molecular pathophysiology of renal interstitial fibrosis

The kidneys play a key role in maintaining total body homeostasis. The complexity of this task is reflected in the unique architecture of the organ. Ureteral obstruction greatly affects renal physiology by altering hemodynamics, changing glomerular filtration and renal metabolism, and inducing architectural malformations of the kidney parenchyma, most importantly renal fibrosis. Persisting pathological changes lead to chronic kidney disease, which currently affects ∼10% of the global population and is one of the major causes of death worldwide. Studies on the consequences of ureteral obstruction date back to the 1800s. Even today, experimental unilateral ureteral obstruction (UUO) remains the standard model for tubulointerstitial fibrosis. However, the model has certain limitations when it comes to studying tubular injury and repair, as well as a limited potential for human translation. Nevertheless, ureteral obstruction has provided the scientific community with a wealth of knowledge on renal (patho)physiology. With the introduction of advanced omics techniques, the classical UUO model has remained relevant to this day and has been instrumental in understanding renal fibrosis at the molecular, genomic, and cellular levels. This review details key concepts and recent advances in the understanding of obstructive nephropathy, highlighting the pathophysiological hallmarks responsible for the functional and architectural changes induced by ureteral obstruction, with a special emphasis on renal fibrosis.

Early upregulation of iNOS mRNA expression and increase in NO metabolites in pressurized renal epithelial cells

Pressure is an important physiological regulator, but under abnormal conditions it may be a critical factor in the onset and progression of disease in many organs. In vivo, proximal tubular epithelial cells are subjected to pressure as a result of ureteral obstruction, which may influence the production of nitric oxide (NO), a ubiquitous multifunctional cytokine. To directly explore the effect of pressure on the expression and activity of NO synthase (NOS) in cultured proximal tubular epithelial cells, a novel pressure apparatus was developed. Cells were subjected to pressures of 20-120 mmHg over time (5 min-72 h). RT-PCR demonstrated an increase in inducible NOS (iNOS) and sGC, while endothelial NOS remained unchanged. Real-time PCR (qPCR) confirmed an earlier induction of iNOS transcript subjected to 60 mmHg compared with cytokine mix. iNOS protein expression was significantly increased following 60 mmHg of pressure for 24 h. Use of nuclear factor-kappaB inhibitors was shown to prevent the increase in iNOS expression following 60 mmHg for 2 h. NO and cGMP were increased with the application of pressure. The addition of the irreversible iNOS inhibitor (1400W) was shown to prevent this increase. We demonstrate that with the use of a simply designed apparatus, pressure led to an extremely early induction of iNOS and a rapid activation of NOS activity to increase NO and cGMP in proximal tubule epithelial cells. The rapid effects of pressure on iNOS may have important implications in the obstructed kidney.

Renal vein Doppler sonography of obstructive uropathy

OBJECTIVE

Obstructive uropathy in the early stages can be difficult to diagnose using either standard sonography or the arterial resistive index. We tested the hypothesis that acute obstruction of the renal collecting system reduces the intraparenchymal renal compliance, which affects the intraparenchymal venous blood flow to a greater degree than the arterial flow.

SUBJECTS AND METHODS

Twelve patients with clinical evidence of acute obstructive uropathy were referred for helical CT to confirm the diagnosis and to provide a gold standard by which we could evaluate the sonographic findings in the 12 test patients. Twelve patients without renal disease served as a control group. Doppler sonography of the interlobar arteries and veins of both kidneys then was performed, with the sonographer unaware of which kidney had an obstruction. Peak venous flow measurements and arterial resistive and venous impedance indexes were obtained. The impedance indexes of the obstructed and unobstructed kidney were compared for each patient.

RESULTS

The mean arterial resistive indexes of the obstructed kidneys were larger than those of the unobstructed kidneys, 0.67 +/- 0.08 and 0.62 +/- 0.05, respectively (p = 0.05). The venous impedance indexes comparing obstructed and unobstructed sides were 0.38 +/- 0.25 and 0.80 +/- 0.25, respectively, a statistically significant result (p = 0.0002). On average, the peak venous flow signal in the obstructed kidney was 69% higher than that of the unobstructed kidney (p = 0.04) and 86% higher than that of the peak venous flow signal in the control group (p = 0.005).

CONCLUSION

Renal obstruction alters the venous flow to a greater extent than the arterial flow, and a comparison between the venous flow in the obstructed and unobstructed kidneys may improve diagnostic accuracy.

The absence of a triphasic renovascular response by the multicalyceal kidney of the primate in reaction to acute, complete, unilateral, ureteric obstruction

The early renovascular response by the ipsilateral kidney to acute, total, unilateral, ureteric obstruction was investigated in the adult male chacma baboon (Papio ursinus). Complete occlusion was effected by ligating the ureter at the brim of the bony pelvis ("N"=10). Sham studies were enacted using the same method but the ureter was not obstructed ("N"=11). Haemodynamic reactions were monitored for 12 hours. Compared with the sham-occluded set, the renal pelvic pressures in the obstructed group were significantly increased (P<0.05) from the second hour of the inquiry. However, there were no significant differences in renal blood flow, either between or within the respective cohorts. In this study, the renovascular response to acute ureteric occlusion was similar to that displayed by the multicalyceal kidney of other species under identical conditions. This reaction was fundamentally different to that exhibited by the unicalyceal kidney under similar circumstances.

Renal hemodynamic changes after complete and partial unilateral ureteral obstruction in the fetal lamb

PURPOSE

Complete and partial ureteral obstruction decreases ipsilateral renal blood flow in neonatal and adult animals. However, the effects of obstruction that develops during gestation may be different from those in neonatal or adult animals. We determine whether complete or partial ureteral obstruction decreases ipsilateral renal blood flow in fetal sheep.

MATERIALS AND METHODS

We positioned an ultrasonic flow transducer around both renal arteries in 21 fetal sheep at 123 to 125 days of gestation. Unilateral ureteral obstruction was created in 16 fetuses, including complete and partial obstruction in 7 and 9, respectively. There were 5 controls. Renal blood flow and arterial blood pressure were measured daily for a minimum of 7 days.

RESULTS

All obstructed kidneys had hydronephrosis, partially obstructed kidneys had less obstruction and contralateral kidneys had none. Renal weight was similar in obstructed and contralateral kidneys in the sham operated, partial and complete obstruction groups. After partial ureteral obstruction renal blood flow in obstructed and contralateral kidneys was increased compared to that in sham operated kidneys up to 11 days after obstruction was created. After complete ureteral obstruction the blood flow in obstructed kidneys was significantly lower than in the unobstructed counterparts but it remained 124% of initial renal blood flow at 10 days. Elevated ureteral pressure was maintained in obstructed kidneys throughout the study period.

CONCLUSIONS

In our experiment partial ureteral obstruction in the fetus did not decrease renal blood flow to the ipsilateral kidney even after 7 days. Complete obstruction decreased blood flow in the affected kidney but not to same magnitude as that in previous adult animal studies. Our findings suggest that during gestation renal blood flow is maintained in the presence of obstruction.