Renal parenchymal tolerance to artery occlusion: a time and damage study in rats developing collateral circulation

With a Little Help From My Friends: the Role of the Renal Collateral Circulation in Atherosclerotic Renovascular Disease

The collateral circulation can adapt to bypass major arteries with limited flow and serves a crucial protective role in coronary, cerebral, and peripheral arterial disease. Emerging evidence indicates that the renal collateral circulation can similarly adapt and thereby limit kidney ischemia in atherosclerotic renovascular disease. These adaptations predominantly include recruitment of preexisting microvessels for arteriogenesis, with de novo vessel formation playing a limited role. Yet, adaptations of the renal collateral circulation in renovascular disease are often insufficient to fully compensate for the limited flow within an obstructed renal artery and may be hampered by the severity of obstruction or patient comorbidities. Experimental strategies have attempted to circumvent limitations of collateral formation and improve the prognosis of patients with various ischemic vascular territories. These have included pharmacological approaches such as endothelial growth factors, renin-angiotensin-aldosterone system blockade, and If-channel-blockers, as well as interventions like preconditioning, exercise, enhanced external counter-pulsation, and low-energy shock-wave therapy. However, few of these strategies have been implemented in atherosclerotic renovascular disease. This review summarizes current understanding regarding the development of renal collateral circulation in atherosclerotic renovascular disease. Studies are needed to apply lessons learned in other vascular beds in the setting of atherosclerotic renovascular disease to develop new treatment regimens for this patient group.

Peristenotic Collateral Circulation in Atherosclerotic Renovascular Disease: Association With Kidney Function and Response to Treatment

The significance of peristenotic collateral circulation (PCC) development around a stenotic renal artery is unknown. We tested the hypothesis that PCC is linked to loss of kidney function and recovery potential in patients with atherosclerotic renovascular disease (ARVD). Thirty-four patients with ARVD were assigned to medical-therapy with or without revascularization based on clinical indications. The PCC was visualized using multidetector computed tomography and defined relative to segmental arteries in patients with essential hypertension. PCC number before and 3 months after treatment was correlated with various renal parameters. Thirty-four stenotic kidneys from 30 patients were analyzed. PCC number correlated inversely with kidney volume. ARVD-stenotic kidneys with baseline PCC (collateral ARVD [C-ARVD], n=13) associated with elevated 24-hour urine protein and stenotic kidney vein level of tumor necrosis factor-α, lower single-kidney volume and blood flow, and greater hypoxia than in stenotic kidneys with no PCC (no collateral ARVD [NC-ARVD], n=17). Revascularization (but not medical-therapy alone) improved stenotic kidney function and reduced inflammation in both NC-ARVD and C-ARVD. In C-ARVD, revascularization also increased stenotic kidney volume, blood flow, and oxygenation to levels comparable to NC-ARVD, and induced PCC regression. However, revascularization improved systolic blood pressure, plasma renin activity, and filtration fraction only in NC-ARVD. Therefore, patients with C-ARVD have greater kidney dysfunction, atrophy, hypoxia, and inflammation compared with patients with NC-ARVD, suggesting that PCC does not effectively protect the stenotic kidney in ARVD. Renal artery revascularization improved in C-ARVD stenotic kidney function, but not hypertension or renin-angiotensin system activation. These observations may help direct management of patients with ARVD.

Hemodynamic determinants of perivascular collateral development in swine renal artery stenosis

BACKGROUND

Renal artery stenosis (RAS) resulting in reduced renal blood flow (RBF) is a common cause of secondary hypertension and deterioration of renal function, which may lead to end-stage renal disease. Recruitment and formation of periarterial collateral vessels may serve to bypass RAS and restore distal blood supply. We hypothesized that development of collaterals around RAS may preserve kidney function.

METHODS

Collateral formation index (CI) was assessed using multidetector computed tomography as fractional vascular volume surrounding the stenosis in 31 pigs with unilateral RAS. Single kidney RBF and glomerular filtration rate (GFR) were also measured.

RESULTS

Of 25 pigs that developed significant stenosis (≥65%), 8 demonstrated minor collateral development (CI < 0.3), and 17 showed major collateral development (CI ≥ 0.3). The degree of RAS was significantly higher in pigs with major collaterals compared with pigs with minor collaterals, and poststenotic kidney cortical volume, perfusion, RBF, and GFR were significantly lower. In a subset of pigs matched for the degree of RAS, RBF and GFR remained lower in pigs with major collaterals.

CONCLUSIONS

We conclude that collaterals develop in animals with significant RAS in proportion to its severity and might be triggered by distal injury, such as decreases in cortical volume and perfusion. However, development of collaterals was unable to confer measurable benefits for stenotic kidney function distal to severe RAS.

Reassessment of the vascularization of renal subcapsular islet grafts

OBJECTIVES

The purpose of this study was to evaluate the functional significance of the renal capsular vessels in renal subcapsular islet grafts.

METHODS

Syngeneic islets were transplanted under the left renal capsule of diabetic Wistar-Furth rats. At 4 weeks post-transplantation, the left renal artery and vein were ligated (group A); in group B, the left renal capsule was dissected to remove capsular vessels; or both were performed in group C. Controls included ligation of the right renal vessels (group D).

RESULTS

: All recipients achieved normoglycemia post-transplantation. Treatments for groups A, B, and D did not result in significant changes in glycemia and glucose tolerance. In contrast, all rats in group C returned to hyperglycemia immediately post-treatment. Insulin contents in grafts harvested at 10 days post-treatment in groups A and B were significantly lower than those in group D but higher than those in group C. Histologic examination revealed well-preserved insulin-positive cells under the capsule of necrotic kidney at 8 weeks post-treatment in group A.

CONCLUSIONS

Renal subcapsular islet grafts do not acquire their blood supply solely from the renal artery but rather from the renal capsular arteries as well. Not only renal veins but also renal capsular veins play a role as effluent vessels from these grafts.

A serum-free in vitro model of renal microvessel development

The differentiation and organization of the embryonic renal vasculature is a crucial event in renal development. To study this process, we developed a serum-free in vitro model of renal microvessel development. Mouse embryonic kidney explants, when embedded specifically in type I collagen, demonstrate outgrowth of microvascular structures when stimulated by the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA, 10-50 ng/ml). Other polypeptide growth factors stimulated little, if any, microvessel outgrowth from the explants. Similar outgrowths were not observed when other embryonic tissue explants were used. The number of microvessels observed depended on the gestational age of the explants. We hypothesize that TPA induces the in situ differentiation of metanephric mesenchymal cells into endothelial cell precursors and that specific matrix proteins and cell-matrix interactions are necessary for the organization of these precursors into microvessels. Our model will allow us to examine in detail the responsiveness of metanephric kidney cells to both growth factors and extracellular matrix molecules and to understand how they influence renal endothelial cell differentiation.

Obstructive aortic and renal thrombosis in the newborn--spontaneous recovery

A 13-day-old infant presented with acute renal failure secondary to a large thrombus formation involving the umbilical aorta and both renal arteries. The initial clinical manifestations were hematuria, followed by anuria, severe dehydration, grunting respirations, and cyanosis of her feet. She was treated with intravenous fluids and peritoneal dialysis. At the onset, there was no blood flow into the abdominal aorta or into the kidneys. Heparinization and fibrinolytic therapies were unsuccessful in dissolving the clot. However, the aortic clot recanalized spontaneously a few weeks later, but the renal arteries remained permanently occluded. Despite this, her kidneys showed blood flow bilaterally and she recovered her renal function, probably by reperfusing her kidneys through collateral circulation. Malignant hypertension ensued after improvement of renal function, but it could be controlled by appropriate antihypertensive therapy.

Restoration of kidney function after prolonged renal artery occlusion

An 11-month-old child developed renal artery occlusion (RAO) and anuric renal failure following an unsuccessful transluminal renal artery angioplasty of a solitary kidney. Despite the prolonged period of anuria, kidney viability was suspected based upon preservation of kidney length and the absence of glomerulosclerosis. At 19 months of age, revascularization of the kidney was performed. During the 7 months following revascularization, renal function gradually improved so that dialysis was no longer necessary. This improvement occurred in spite of significant tubular atrophy. Kidney viability may have been preserved, despite prolonged ischemia, as a result of the decreased renal oxygen consumption that existed during subfiltration glomerular perfusion pressures. The low normal blood erythropoietin level may have reflected the lack of renal hypoxia. The ability of the kidney to adapt to chronic ischemia underscores the importance of considering vascular reconstruction in all patients with RAO despite a long period of non-function.

Thrombosis of the renal artery of a small, solitary kidney: successful return of renal function after prolonged anuria

In the presence of a single functioning kidney, renal artery obstruction produces anuria, which can require hemodialysis. If the problem is diagnosed immediately and surgical intervention is not delayed, revascularization of the ischemic kidney is usually successful. Few authors, however, have reported the return of function to a small solitary kidney after occlusion lasting longer than 2 hours. We describe a case that involved thrombosis of the renal artery to an 8-cm solitary kidney; a successful endarterectomy was performed 29 hours after the onset of anuria. This case shows that the reversibility of renal ischemia is not necessarily determined by either the duration of occlusion or the size of the affected kidney.

[Transluminal dilatation and other nonsurgical catheter technics in the treatment of renovascular hypertension]

The development of percutaneous transluminal techniques has brought up new possibilities for causative treatment of renovascular hypertension. In renal artery stenosis transluminal angioplasty is meanwhile routinely applied; experience with angioplasty to date exceeds by far the number of 1000 published cases. Technical success is obtained in more than 90%. The clinical success in the therapy of reno-vascular hypertension is approximately 76% over all with nearly equal cure and improvement rates. In fibromuscular stenosis clinical success has been obtained in 95% with a cure rate of 56% and improval in 39%. The cure rate is particularly low in patients with atherosclerotic stenosis with 19%, however in 60% improvement has been obtained, resulting in clinical benefit in 79%. Results obtained by surgery seem to be superior to those of dilatation, especially with regard to cure rates. However, the differences are minor and are compensated by the evident advantages of transluminal dilatation, especially its easy application and lower risk. Thus, 8 years after its introduction in nephrology, transluminal dilatation is the therapy of choice in renal artery stenosis. Other nonoperative interventional techniques, including transcatheter aspiration and embolectomy, intraarterial thrombolysis, embolisation and modified angioplasty provided valuable alternatives to usual surgical therapy. However, experience with some of these procedures is still limited. The complication rate of transluminal angioplasty of 10-20%, necessitating surgery in nearly 5%, prohibits its uncritical use.

Successful surgical treatment of anuria caused by renal artery occlusion

Anuria resulting from obstruction of the renal arteries to both Kidneys or to a solitary kidney is unusual. The tolerance of the kidney to this ischemia is largely dependent upon the presence of collaterals, stimulated by pre-existing arterial disease. Our experience with six patients with anuria caused by renal artery occlusion supports the role of revascularization in the recovery of significant renal function. Four of these patients had hypertension, impaired renal function, and the existence of collateral circulation to an ischemic kidney, prior to occlusion, while two patients had normal renal function (serum creatinine = 0.5 and 0.9 mg/dl) before occlusion. The intervals of anuria for the two previously normal kidneys were six hours and five days, and 2 to 14 days in the four patients with vascular disease. Isotope scanning suggested renal artery occlusion in two patients, but arteriograms confirmed the diagnosis in all six. A thrombectomy restored blood flow through the two previously normal renal arteries. Grafts from the aorta or celiax axis were used for three patients and the splenic artery was used for the sixth patient. Urine flow began during or soon after operation in all patients. Dialysis was necessary for 30 and 45 days in the two patients with normal kidneys, but in only one of the four patients with previous disease (for ten days). Serum creatinine decreased to <2.0 mg/dl after operation, except in the man with a solitary kidney, who five years later has a creatinine of 3 mg/dl. All four patients with previous arterial disease died from cardiac failure within 1 to 30 months after operation. Therefore, anuria of acute onset should be evaluated by renal scan and arteriogram to detect those patients with proximal renal artery occlusion in preparation for revascularization.

Collateral circulation in stenosis or occlusion of the renal artery

The abdominal angiograms of 381 patients were critically reexamined for the existence of collateral circulation in cases of renal artery stenosis or occlusion. Typical renal artery stenosis was found in 39 patients; among these, 17 had a collateral circulation, which was extrarenal in 15 and intrarenal in two. Collateral circulation involving the lumbar arteries was most common. In two patients a collateral circulation was established via the inferior mesenteric artery.

Severe blunt trauma of upper urinary and intestinal tracts in a child

A 7 1/2-year-old boy sustained severe trauma to the upper abdomen, including transection of the common bile duct, transection of the second part of the duodenum, contusion of the head of the pancreas, traumatic thrombosis of the left renal artery, thrombosis of the right lower pole renal vasculature and avulsion of the right renal pelvis. A staged elective repair of the upper urinary tract, and later the upper gastrointestinal tract, was accomplished when he was referred 5 1/2 months after the initial injury.

Collateral circulation after renal artery occlusion in the rat

We used angiographic and microsphere methods to evaluate the anatomic and functional features of renal collateral circulation in the rat. By the microsphere method, renal parenchymal blood flow was less than 1% of control 1 hour after occlusion of the main renal artery; 2.8% of control 1-2 weeks after arterial occlusion; and 1% of control 4-9 weeks after occlusion. Radiographic observations during chronic occlusion revealed numerous collateral vessels to the kidney. These vessels readily filled with angiographic contrast medium but the intrarenal circulation did not visualize. We conclude that collateral circulation to renal parenchyma is negligible after acute or chronic occlusion of the main renal artery in the rat. The rich anatomic plexus of collateral vessels has no functional significance and is unable to preserve viability of the parenchyma.