Analysis of myogenic mechanisms in renal autoregulation

Relation between Cajal Cell Density and Radiological and Scintigraphic Outcomes in Patients with Ureteropelvic Junction Obstruction

INTRODUCTION

In this study, we aimed to investigate the correlation between Cajal cell density and preoperative and postoperative radiological and scintigraphic parameters in ureteropelvic junction obstruction (UPJO).

METHODS

The study group consisted of 41 renal units (38 consecutive patients; 13 female and 25 male) surgically treated for UPJO. UPJ specimens from patients were immuno-stained with CD117 (c-kit) antibody for interstitial Cajal cells (ICCs). The relation between Cajal cell density and preoperative and postoperative radiological and scintigraphic parameters was evaluated.

RESULTS

The mean age of the patients was 8.52 ± 8.86 (0-35) years. The density of Cajal cells was defined in 2 groups for convenient analysis as 0-5 cells (low) in 19 (46.3%) patients and >5 cells (moderate-high) in 22 (53.6%). There was significant difference between the preoperative and postoperative anteroposterior diameters of the related kidneys in both Cajal groups (p = 0.001-low, p = 0.000-moderate-high) independent of Cajal cell density. Regression in hydronephrosis postoperatively was determined in both Cajal groups (77.8%-low, 64.7%-moderate-high); however, there was no difference between them (p = 0.39). Preoperative T1/2 was significantly longer in the low Cajal group (p = 0.02). Postoperative T1/2 decreased in both low (p = 0.000) and moderate-high (p = 0.001) Cajal groups, but no difference was found between them (p = 0.24). There was significant improvement in the kidney differential function after surgery in the low Cajal density group (p = 0.015) while there was no correlation between the scintigraphic success or improvement and Cajal cell density (p = 0.51).

DISCUSSION/CONCLUSION

ICC deficiency/density could not be shown as a predictive factor for the determination of success rate of pyeloplasty. Despite the lack of any evidence for the degree of deficiency as an indicator for the severity of obstruction and prediction of surgical success, further studies are needed for confirmation.

Changes in interstitial cell of Cajal-like cells density in congenital ureteropelvic junction obstruction

PURPOSE

The authors examined the number of interstitial cells of Cajal-like cells (ICC-LCs) in obstructed ureteropelvic junction (UPJ) in comparison with normal UPJ specimens and age-related changes.

MATERIALS AND METHODS

A total of 20 human formalin fixed, paraffin-embedded specimens of intrinsic UPJO from children at the mean age of 8.1 years (age range: 8 months-16.8 years) and 5 control samples from children at the mean age of 2.3 years (range 2.4 months-7.4 years) were investigated immunohistochemically for the expression of c-kit proto-oncogene by light microscopy with computerized image analysis. The results were examined by Fisher's exact test, Yates' chi-square test, and t test for Pearson's correlation coefficient. A P value less than 0.05 was considered statistically significant.

RESULTS

The number of ICC-LCs-dense fields was significantly higher in UPJO specimens in comparison with the normal group (P = 0.0004). The number of ICC-LCs-sparse fields was significantly lowered in UPJO specimens in comparison with the normal group (P = 0.0122). There was no significant difference in the number of ICC-LCs-medium fields in obstructed and normal UPJ specimens. The number of ICC-LCs was decreasing significantly with increasing age of the patients with UPJO (P = 0.0038).

CONCLUSIONS

The higher density of c-kit-positive ICC-LCs in UPJ may manifest the compensation of altered peristalsis in UPJO. The number of ICC-LCs-dense fields decreasing with age may show the failure of compensation and regression of the compensatory changes.

Structural morphology of renal vasculature

An automatic segmentation technique has been developed and applied to two renal micro-computer tomography (CT) images. With the use of a 20-microm voxel resolution image, the arterial and venous trees were segmented for the rat renal vasculature, distinguishing resolving vessels down to 30 microm in radius. A higher resolution 4-microm voxel image of a renal vascular subtree, with vessel radial values down to 10 microm, was segmented. Strahler ordering was applied to each subtree using an iterative scheme developed to integrate information from the two segmented models to reconstruct the complete topology of the entire vascular tree. An error analysis of the assigned orders quantified the robustness of the ordering process for the full model. Radial, length, and connectivity data of the complete arterial and venous trees are reported by order. Substantial parallelism is observed between individual arteries and veins, and the ratio of parallel vessel radii is quantified via a power law. A strong correlation with Murray's Law was established, providing convincing evidence of the "minimum work" hypothesis. Results were compared with theoretical branch angle formulations, based on the principles of "minimum shear force," were inconclusive. Three-dimensional reconstructions of renal vascular trees collected are made freely available for further investigation into renal physiology and modeling studies.

Analysis of the tubuloglomerular feedback mechanism in renal autoregulation

Along the juxtaglomerular segment of the afferent arteriole the luminal pressure p approaches the glomerular capillary pressure of 55-60 mmHg. At such low luminal pressures the myogenic mechanism contracts only if extravascular pressure p(ex) is subatmospheric. According to Poiseuille's formula complete autoregulation requires that blood flow is F=5Kr(0)(4)/Deltax at arterial pressures exceeding 65 mmHg; r(0) is the radius of the relaxed segment at transmural pressure p - p(ex) < or =60 mmHg, where p(ex) is the extravascular pressure; Deltax is the length of the main preglomerular segment, 10 times longer than the juxtaglomerular segment. Consistent with in vitro studies a myogenic mechanism may reduce the relaxed juxtaglomerular radius r(jx)=0.7r(0) by 40% at a transmural pressure of 140 mmHg. Fifty and 60% reductions are also considered. Integration of Poiseuille's formula shows that complete autoregulation of preglomerular blood flow requires negative extravascular pressures p(ex)= -90 to -55 mmHg dependent on contractile force. Negative pressure of this magnitude is generated by effective hyperosmolality <5 mOsm across the membrane separating cleft from pole cushion. Negative pressure stays constant at arterial pressures exceeding 90-110 mmHg, implying constant tubuloglomerular feedback, but approaches atmospheric pressure at lower arterial pressure, suggesting maintenance of blood flow by reduction in the glomerular filtration rate; a rise in macula densa concentrations [NaCl](md) by 0.15 mM or [NaHCO(3)](md) by 2 mM raises extravascular pressure towards atmospheric levels by approximately 40 mmHg. A 40-mmHg rise in interstitial pressure exerts the same effect. Loop diuretics nullify osmotic force and dilate juxtaglomerular and main segments by raising juxtaglomerular extravascular pressure towards atmospheric levels.