Renal angiotensin converting enzyme promotes renal damage during ureteral obstruction

Angiotensin Receptor Blocker Losartan Inhibits Spontaneous Motility of Isolated Human Ureter

BACKGROUND AND OBJECTIVES

Ureteral motility is essential for elimination of intraluminal stones, and it may be adversely affected by cardiovascular drugs that a patient is taking chronically. The aim of our study was to test whether ACE inhibitors and an angiotensin receptor blocker may influence spontaneous contractions of isolated human ureter.

METHODS

Both phasic and tonic contractions of the isolated ureteral segments taken from 10 patients were measured as changes of the longitudinal tension or pressure recordings. Captopril, enalapril and losartan were separately added to the organ baths cumulatively.

RESULTS

While enalapril (2.7 × 10^-7-3.9 × 10^-4 M) and captopril (6.1 × 10^-7-2.7 × 10^-3 M) did not affect either spontaneous activity or tone of isolated ureteral segments, losartan (2.9 × 10^-7-4.2 × 10^-4 M) caused concentration-dependent inhibition of spontaneous contractions of the segments (50 % effective concentration (EC₅₀) = 13.46 ± 1.80 × 10^-6 M; F = 10.72, r = 0.79, p < 0.001).

CONCLUSIONS

Due to differences in molecular mechanism of action, angiotensin receptor blocker losartan does and ACE inhibitors captopril and enalapril do not inhibit spontaneous contractions of isolated human ureter.

Effect of angiotensin II and small GTPase Ras signaling pathway inhibition on early renal changes in a murine model of obstructive nephropathy

Tubulointerstitial fibrosis is a major feature of chronic kidney disease. Unilateral ureteral obstruction (UUO) in rodents leads to the development of renal tubulointerstitial fibrosis consistent with histopathological changes observed in advanced chronic kidney disease in humans. The purpose of this study was to assess the effect of inhibiting angiotensin II receptors or Ras activation on early renal fibrotic changes induced by UUO. Animals either received angiotensin II or underwent UUO. UUO animals received either losartan, atorvastatin, and farnesyl transferase inhibitor (FTI) L-744,832, or chaetomellic acid A (ChA). Levels of activated Ras, phospho-ERK1/2, phospho-Akt, fibronectin, and α-smooth muscle actin were subsequently quantified in renal tissue by ELISA, Western blot, and/or immunohistochemistry. Our results demonstrate that administration of angiotensin II induces activation of the small GTPase Ras/Erk/Akt signaling system, suggesting an involvement of angiotensin II in the early obstruction-induced activation of renal Ras. Furthermore, upstream inhibition of Ras signalling by blocking either angiotensin AT1 type receptor or by inhibiting Ras prenylation (atorvastatin, FTI o ChA) reduced the activation of the Ras/Erk/Akt signaling system and decreased the early fibrotic response in the obstructed kidney. This study points out that pharmacological inhibition of Ras activation may hold promise as a future strategy in the prevention of renal fibrosis.

Contribution of the renin-angiotensin system to the intrarenal resistive index in chronic unilateral partial ureteral obstruction in dogs

PURPOSE

We investigated the role of the renin-angiotensin system on intrarenal hemodynamics in chronic unilateral partial ureteral obstruction (UPUO) using Doppler ultrasound (US).

METHODS

In 11 dogs with chronic UPUO, we determined the renal resistive index (RI) before and 1 h after the intravenous infusion of an angiotensin-converting enzyme (ACE) inhibitor (captopril), an angiotensin II receptor type 1 (ART1) antagonist (L-158,809), and the combination of these two drugs. Change in resistive index (ΔRI) was calculated as RI after the administration of each tested material minus baseline RI.

RESULTS

At the baseline measurement, significant differences in RI were seen between obstructed and nonobstructed kidneys. ACE inhibitor, ART1 antagonist, or the combination of these drugs did not result in any significant changes in RI in either obstructed or nonobstructed kidneys. However, in obstructed kidneys, ΔRI in the combination of ACE inhibitor and ART1 antagonist were significantly greater than those in ACE inhibitor or ART1 antagonist alone, whereas there were no significant differences in those values in nonobstructed kidneys.

CONCLUSION

These observations suggest that the renin-angiotensin system in dogs with chronic UPUO may not contribute significantly to the differences in intrarenal RI between obstructed and nonobstructed kidneys. However, the angiotensin-producing pathways and angiotensin II receptor subtypes other than ACE and ART1 may have some different effects between obstructed and nonobstructed kidneys.

Molecular biology of ureteral bud and trigonal development

Advances in molecular biology have provided valuable insight into the development of the urinary tract, particularly ureteral bud formation. Reciprocal inductive signals between the ureteral bud and growing kidney are crucial for normal development. The Wolffian duct serves as the site of origin of the ureteral bud and forms distal excretory ducts that are incorporated into the developing bladder to become the trigone. Vesicoureteral reflux and renal dysplasia can result from abnormal position of the ureteral orifice on the trigone. The presumed origin of trigone formation is based largely on evaluation of human and animal models performed nearly a century ago. The trigone is thought to develop from the mesodermal germ cell layer; however, several recent studies have shown that endoderm may be the tissue of origin. This review highlights important discoveries in the field of molecular biology as it relates to the development of normal and abnormal ureteral bud formation. It also describes the anatomic relationship between the developing bud and trigone as it pertains to clinically relevant urinary tract anomalies, including recent discoveries that attempt to prove the origin of the trigone.