Increased urinary excretion of endothelin during hypothermic perfusion preservation in kidneys subjected to preretrieval warm ischemic injury.

The purpose of the study was two-fold: 1) to determine whether endothelin (ET) levels could be detected in the ureteral effluent during hypothermic perfusion preservation (HPP) and; 2) to determine whether preretrieval warm ischemic (WI) injury is associated with increased ureteral excretion of ET. In situ pre-WI injury was induced in Lewis rats (n=10) by a 30-min extrinsic occlusion of the suprarenal aorta. The left kidney underwent 16 hr of HPP, and ureteral effluent (UE) from ischemic and control kidneys (n=10) was collected over 16 hr of HPP. The UE ET concentration and total ET excretion over 16 hr of HPP were significantly higher in kidneys subjected to pre-WI injury compared with nonischemic controls. Kidneys subjected to pre-WI injury can be distinguished from nonischemic control kidneys during HPP by a significantly higher concentration of ET in the UE and a higher overall excretion of ET during HPP.

Identification of kidneys subjected to preretrieval warm ischemic injury by simultaneous monitoring of glomerular filtration and perfusate flow during hypothermic perfusion preservation.

BACKGROUND: Historically, ex vivo physiological evaluation of cadaveric renal allografts has been limited to assessing perfusate flow (PF) during hypothermic perfusion preservation (HPP). Using a small animal model, we have previously described a method for continuous monitoring of glomerular filtration rate (GFR) during HPP. Our study was undertaken to determine if monitoring GFR and PF during HPP distinguished kidneys subjected to preretrieval warm ischemic (WI) injury more reliably than PF alone. METHODS: In situ WI was induced in Lewis rats (n=10) by extrinsic occlusion of the suprarenal aorta for 30 min. After in situ cold perfusion and retrieval, the left kidney underwent 16 hr of HPP. Nonischemic (NI) control kidneys (n=10) were retrieved in the absence of suprarenal aortic occlusion. Longitudinal changes in PF, GFR, and filtration fraction (FF) during HPP were compared in WI versus NI kidneys (FF=GFR/PF x 100%). RESULTS: PF remained the same in both cohorts throughout HPP. GFR, however, increased to a significantly greater degree in WI versus NI kidneys during the first 4 hr of HPP (713+/-401 vs. 26+/-23%, respectively) (P<0.05). The increase in FF at 4 hr was 1203+/-696% in the WI kidneys versus 83+/-46% in the NI controls (P<0.05). CONCLUSIONS: In contrast to PF alone, measurement of both PF and GFR distinguished kidneys subjected to pre-WI from NI controls. The data provide a means to determine if monitoring of both GFR and PF during HPP will predict short- and long-term renal allograft function more reliably than PF alone.

Lovastatin preserves renal function in experimental diabetes.

Although hyperlipidemia has been associated with the progression of glomerulosclerosis, little attention has been directed toward the use of lipid-lowering agents in altering diabetic nephropathy. We tested the hypothesis that lovastatin and the combination of lovastatin and enalapril would preserve renal function in streptozotocin-induced diabetic Wistar rats. Five groups of animals were studied: group 1, nondiabetic (n = 10); group 2, diabetic, insulin only (n = 12); group 3, lovastatin, (15 mg/kg/day, n = 13); group 4, enalapril, (50 mg/L drinking water, n = 10) and group 5, lovastatin plus enalapril, (n = 14). After 8 weeks of treatment, glomerular filtration rate (GFR, insulin clearance) was measured in anesthetized animals. The diabetic group was characterized by a GFR of 0.18 +/- 0.03 ml/min/g of kidney weight (gKW), a blood glucose level of 441 +/- 36 mg/dL, plasma cholesterol and triglyceride levels of 64 +/- 6.0 and 103 +/- 26.0 mg/dL. Lovastatin preserved GFR, 0.52 +/- 0.06 ml/min/gKW compared with the diabetic control subjects (P < 0.05). Enalapril also maintained GFR (0.42 +/- 0.06 ml/min/gKW, P < 0.05). In the lovastatin plus enalapril group, GFR (0.62 +/- 0.05 ml/min/gKW) was greater than in the enalapril group (P < 0.05), but was not different from the lovastatin group. Plasma lipid levels were not altered in any of the groups. Assessment of the kidneys by histology after treatment showed that the mesangial matrix injury score was better in the lovastatin, enalapril, and lovastatin plus enalapril groups compared with the diabetic group (P < 0.05). Lovastatin, enalapril, and lovastatin plus enalapril abrogated the decline in GFR and glomerular injury in diabetic rats. Lovastatin's direct renal protective effect seems to be independent of its lipid-lowering properties.

Increased intra-abdominal pressure during pneumoperitoneum stimulates endothelin release in a canine model.

Prolonged pneumoperitoneum during laparoscopic surgery has been associated with oliguria in clinical experimental studies. Although the pathophysiology of this oliguria is thought to be renal parenchymal and venous compression, the role of the potent vasoconstrictor endothelin (ET) has not been studied. The purpose of this study was to investigate the effect of pneumoperitoneum on endothelin release and renal function in a canine model. Two groups of dogs were studied during pneumoperitoneum (Group 1, N = 7) or isolated left renal vein compression (Group 2, N = 6). Urine and plasma samples were collected for urine output, glomerular filtration rate (GFR), urine sodium, and plasma endothelin measurements. In Group 1, GFR fell significantly (p < 0.05) by 49% from a control of 0.88 +/- 0.12 mL/min per gram of kidney weight. Urine volume fell by 79% (p < 0.05) from a control value of 0.014 +/- 0.003 mL/min/gkw. Sodium excretion was decreased by 88%. Sodium reabsorption was significantly enhanced during pneumoperitoneum (99.56 +/- 0.15% v 98.44 +/- 0.25%). Arterial plasma ET concentrations were elevated by 8% during the first 20 minutes of pneumoperitoneum (30.8 +/- 3.6 v 33.3 +/- 3.4 pg/mL; p < 0.05). In Group 2, left renal vein compression resulted in a 31% decrease (p < 0.05) in GFR in the left kidney and a 25% decrease in the right kidney. Urine volume fell by 67% in the left kidney and 40% in the right. Renal venous ET concentrations also increased after renal vein compression. Although the mechanism by which oliguria occurs during pneumoperitoneum is not fully understood, the ET concentration was elevated. Because ET can decrease RBF, GFR, and sodium excretion, it may contribute to the oliguria observed during long periods of pneumoperitoneum.

Renal microcirculatory effects of lovastatin in a rat model of reduced renal mass.

OBJECTIVES: Patients with reduced renal mass are at increased risk of developing renal failure. A remnant kidney model has been used to study the hemodynamic and structural changes that occur. We recently reported that the lipid-lowering agent lovastatin preserves renal function in this model. The purpose of the present study was to determine the specific effects of lovastation on the renal microcirculation of rats with reduced renal mass. METHODS: We used the rat hydronephrotic kidney preparation with a 5/6 partial nephrectomy. This model allows direct visualization of preglomerular and postglomerular vessels using videomicroscopy. The diameters and vascular responses to acetylcholine and angiotensin II of the interlobular, afferent, and efferent vessels were determined in two groups of animals with renal mass reduction: 15 rats with no lovastatin treatment and 18 rats treated with oral lovastatin (15 mg/kg body weight/day) for 2 weeks. RESULTS: In the lovastatin-treated rats, the baseline efferent vessel diameter was smaller by 21% (P < 0.05), but the interlobular and afferent vessel baseline diameters were not different from those in the untreated rats. Serum creatinine levels were lower in the treated rats (1.5 +/- 0.1 versus 2.0 +/- 0.2 mg/dL, P < 0.05), but serum lipids were not different. In the lovastatin-treated rats, vascular reactivity to acetylcholine was enhanced in the afferent and decreased in the efferent vessels. CONCLUSIONS: In this renal ablation model, lovastatin preserved renal function as measured by serum creatinine without lowering plasma lipid levels. Lovastatin treatment resulted in smaller efferent vessel diameters. Lovastatin also increased the vasodilatory response to acetylcholine in the afferent vessels. Together, these preglomerular and postglomerular changes would increase the single-nephron glomerular filtration rate. The renal protective effect of lovastatin may be due to these vasoactive effects on the renal microcirculation.

Renal hemodynamic effects of lovastatin in a renal ablation model.

OBJECTIVES: Patients with renal mass reduction of more than 50% are at increased risk for progressive renal failure. Lipid-lowering agents have been shown to preserve renal function in various models of chronic renal failure. This study was performed to evaluate the hemodynamic effects of lovastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, in the remnant kidney model. METHODS: Two groups of animals were studied. Group 1 (n = 9) served as controls and group 2 (n = 14) received lovastatin, 15 mg/kg/day orally, for 2 weeks after renal ablation. Glomerular filtration rate (GFR, inulin clearance), renal blood flow (RBF, ultrasonic flow probe), and 24-hour protein excretion were measured in anesthetized rats. RESULTS: Two weeks after renal ablation, GFR was 0.28 +/- 0.09 mL/min/gkw (gram kidney weight) in group 1, whereas in group 2, lovastatin preserved GFR at 0.58 +/- 0.3 mL/min/gkw (P < 0.05). RBF in group 1 was 1.2 +/- 0.2 mL/min/gkw and increased to 2.1 +/- 0.4 mL/min/gkw in group 2 (P < 0.05), representing a 43% increase. Protein excretion decreased significantly to 13 +/- 1.7 mg/24 hr in group 2. The lovastatin-treated group had a lower serum cholesterol (59 +/- 3 mg/dL versus 71 +/- 2 mg/dL, P < 0.05), but serum triglyceride levels were not different between the two groups. CONCLUSIONS: Lovastatin preserves renal function in a renal ablation model after 2 weeks of treatment. It specifically increased total RBF. Therefore, in addition to its known cholesterol lowering effect, lovastatin also has the direct renal hemodynamic effect of increasing RBF and maintaining GFR.

Lovastatin has direct renal hemodynamic effects in a rodent model.

PURPOSE: Lovastatin, an HMG-CoA reductase inhibitor, has been shown to preserve renal function in models of chronic renal failure. We determined the effect of lovastatin on renal function and hemodynamics in normal nonpathologic kidneys in a rodent model. MATERIALS AND METHODS: Renal function was measured in anesthetized (Inactin) control rats (n = 13) and lovastatin-treated rats (15 mg./kg./day, 3 weeks, orally, n = 17). Renal blood flow was measured with an ultrasonic flowprobe, and glomerular filtration rate was measured by inulin clearance. The effect of lovastatin on pre- and postglomerular vessel diameters was also observed in a hydronephrotic kidney preparation by videomicroscopy. RESULTS: Lovastatin significantly increased (p < 0.05) renal blood flow and glomerular filtration rate by 17% (3.4 +/- 0.2 ml./min./gram kidney weight (gKW) versus 2.9 +/- 0.2 ml./min./gKW) and 49% (0.67 +/- 0.04 ml./min./gKW versus 0.45 +/- 0.06 ml./min./gKW). The increase in renal blood flow was mediated by preglomerular vasodilation (expressed as percent increase from baseline diameter, n = 20), 25% in the interlobular artery and 20% in the afferent arteriole (p < 0.05). CONCLUSIONS: In addition to its known lipid-lowering properties, lovastatin has a direct renal hemodynamic effect, increasing renal blood flow and glomerular filtration rate in normal nonpathologic kidneys. Lovastatin's selective preglomerular vasodilation may account for the observed increase in renal blood flow and glomerular filtration rate. Accordingly, this additional hemodynamic effect may be useful in preserving renal function in models of chronic renal failure.

Dietary myo-inositol restores diabetic renal arteriolar reactivity to angiotensin II but not to norepinephrine.

OBJECTIVE: This study addresses the hypothesis that the diminished constriction of renal arterioles to angiotensin II (Ang II) and norepinephrine (NE) in diabetic rats is due to elevated activity in the polyol pathway. This activity results in reduced incorporation of myo-inositol into membrane phospholipids and impaired signal transduction. METHODS: The left ureter of female Wistar rats (140-160 g) was surgically ligated. Four to six weeks later, streptozotocin (50 mg/kg, i.p.) was injected in half of the rats in induce diabetes. Beginning on the day of streptozotocin injection, diabetic and nondiabetic rats were fed either a standard diet or a diet enriched with 1% myo-inositol. Seven to 10 days later, all rats were anesthetized and the hydronephrotic kidney was bisected and exteriorized in a bath for direct visualization of the renal microvasculature. The constrictor responses of interlobular, afferent, and efferent arterioles to Ang II or NE (applied to the bath) were directly quantitated by in vivo microscopy. RESULTS: Among diabetic rats, the myo-inositol-enriched diet significantly enhanced the constriction of interlobular, afferent, and efferent arterioles in response to Ang II, so that the responses to the peptide were almost completely restored to normal. Constriction to NE by interlobular arteries and afferent arterioles (but not efferent arterioles) was also significantly attenuated among diabetic rats fed the standard diet. However, unlike what was observed for Ang II, the myo-inositol-enriched diet did not enhance constriction to NE among diabetic rats. CONCLUSIONS: These data indicate that different mechanisms are responsible for decreased renal arteriolar constriction due to Ang II and NE in early diabetes. Diminished arteriolar constriction due to Ang II, but not to NE, may be linked to altered myo-inositol metabolism.

Acute spermatic cord torsion alters the microcirculation of the contralateral testis.

PURPOSE: The purpose of this study was to characterize the hemodynamic changes in the contralateral testis during acute spermatic cord torsion in anesthetized rats. MATERIALS AND METHODS: We used videomicroscopy to examine the microcirculation of the contralateral testis following acute torsion. Specifically, we examined the effect on vasomotion, a rhythmic dilation and constriction of the arterioles that is involved in fluid and nutrient exchange and modulation of local vascular resistance. In a separate set of experiments, blood flow in the contralateral internal spermatic artery was measured with an ultrasonic flow probe during acute torsion. RESULTS: Following 720 degrees torsion, the amplitude of vasomotion in the contralateral testis increased 121% (29.0 +/- 3.9% versus 13.0 +/- 1.7%) compared with controls. Blood flow in the contralateral internal spermatic artery decreased 43% after 2 hours' torsion. CONCLUSIONS: Acute spermatic cord torsion altered the microcirculation by increasing the amplitude of vasomotion and decreased total blood flow to the opposite testis. Because the hydraulic resistance of a blood vessel exhibiting vasomotion is always less than a vessel with the same average but static diameter, the observed microcirculatory changes may be an adaptive response to preserve local flow in the presence of decreased total flow. The long-term consequences of these changes in the microcirculation may affect testicular function and ultimately fertility.

Diagnostic tunica vaginoscopy in a rodent model of testicular torsion.

OBJECTIVES: To evaluate the effectiveness of percutaneous endoscopy of the tunica vaginalis for identifying testicular torsion in a rodent model. METHODS: One testis was randomly selected in 10 Wistar rats weighing 500 to 600 g. Following 2 hours of 720 degree torsion, bilateral percutaneous endoscopy of the tunica vaginalis was performed by a blinded investigator utilizing a 70 degree cystoscope lens through a single midline 3 to 4 mm scrotal cutdown incision. RESULTS: Using this technique, the blinded investigator was able to identify the torsed testis rapidly in every case, which was distinguished by its cyanotic color and by the size and color of the testicular surface vessels. CONCLUSIONS: Tunica vaginoscopy is a simple, accurate, rapidly performed, minimally invasive, diagnostic technique in this experimental model of testicular torsion.

Role of endothelium-derived relaxing factor in the maintenance of renal blood flow in a rodent model of chronic hydronephrosis.

OBJECTIVES: To define the role of endothelium-derived relaxing factor (EDRF) in the regulation of renal hemodynamics in the hydronephrotic kidney. METHODS: Experiments were performed in control rats and in rats that had undergone unilateral ureteral ligation 6 weeks before. Renal blood flow was monitored before and after inhibition of EDRF synthesis in the control and hydronephrotic animals. Videomicroscopy was also performed in hydronephrotic animals to observe directly the effect of inhibition of EDRF synthesis on the renal microcirculation. RESULTS: Inhibition of EDRF synthesis resulted in a 61% decrease in renal blood flow in the control animals compared with only a 27% decrease for the hydronephrotic animals. The videomicroscopy studies demonstrated that inhibition of EDRF synthesis results in significant vasoconstriction of the preglomerular and postglomerular resistance vessels. CONCLUSIONS: Although EDRF continues to play a significant role in the maintenance of renal blood flow in the chronically obstructed kidney, EDRF synthesis by the renal vascular endothelium may be reduced in this setting, contributing to ischemic renal atrophy.

Dietary protein does not alter intrinsic reactivity of renal microcirculation to angiotensin II in rodents.

The effect of dietary protein on renal function and on renal microvascular reactivity to angiotensin II was determined in rats fed a high-protein diet (40% protein), a low-protein diet (6% protein), or a normal diet (23% protein). Inulin clearance was higher in high-protein-fed rats (n = 7) than in rats fed a low-protein diet (n = 7), 0.88 +/- 0.14 (means +/- SE) vs. 0.54 +/- 0.07 ml.min-1.g kidney wt-1 (P < 0.05). We also used videomicroscopy to assess the effect of angiotensin II on the renal microcirculation in a hydronephrotic kidney preparation. The afferent and efferent arterioles constricted to angiotensin II and norepinephrine in both high- and low-protein-fed rats; this constriction was diminished to angiotensin II but not to norepinephrine, in rats fed a high-protein diet (-24.3 +/- 4.5, -20.2 +/- 4.2%) compared with rats fed a low-protein diet (-39 +/- 5.1, -39.1 +/- 5.7%). The vasoconstrictor responses to angiotensin II in rats fed a high-protein diet and a normal diet were significantly greater following inhibition of angiotensin II formation with captopril but not in low-protein-fed rats. The apparent high-endogenous level of angiotensin II among rats fed a high-protein diet may account for the diminished reactivity to exogenous angiotensin II. Thus alterations in intrinsic vascular reactivity to angiotensin II are not responsible for the altered hemodynamics associated with dietary protein.

Role of the renal microcirculation in antihypertensive therapy.

BACKGROUND: The renal circulation plays a central role in regulating blood pressure and glomerular filtration. OBJECTIVE: To examine the effects of the various classes of antihypertensive agents on the renal microcirculation. SUMMARY: Peripheral vascular resistance is generally increased in hypertension, and the microcirculation makes the major contribution to resistance. In the kidney, the preglomerular and postglomerular vessels constrict to protect the glomerular capillary from increased hydrostatic pressure, further increasing peripheral resistance. Because the renal microcirculation adjusts to maintain glomerular filtration and blood flow, antihypertensive agents that can normalize the pressure and blood flow in these vessels may help prevent the long-term consequences of hypertension. Angiotensin-converting enzyme inhibitors directly affect preglomerular and postglomerular resistance, but they further decrease postglomerular resistance. Calcium antagonists selectively decrease preglomerular resistance. The diuretics, vasodilators, alpha blockers, and beta blockers may also cause changes in preglomerular and postglomerular resistance; however, compensatory reflex responses may mitigate their direct effects. CONCLUSION: Some antihypertensive agents have unique actions on the renal microcirculation that better maintain renal function. A basic understanding of the physiologic action of these agents on the microcirculation may help in their selection.

Reduced renal microvascular reactivity to angiotensin II in diabetic rats.

OBJECTIVE: Renal hyperfiltration in early diabetes is often correlated with increased renal blood flow, reflecting dilation of resistance arterioles. This loss of arteriolar tone has been associated with an impaired reactivity to angiotensin II (Ang II). This study determined if outer cortical arterioles (preglomerular and/or postglomerular) of diabetic rats exhibit a diminished reactivity to Ang II and established if renal vascular prostaglandins account for the diminished responsiveness. METHODS: The constriction of renal microvessels to Ang II (applied to the kidney bath) was quantitated in hydronephrotic kidneys of diabetic rats (7-10 days after streptozotocin treatment) and nondiabetic rats by in vivo videomicroscopy. RESULTS: Interlobular, afferent, and efferent arterioles of diabetic rats were found to be less reactive to Ang II than arterioles of nondiabetic rats. Indomethacin, added to the bath to inhibit renal vascular prostaglandin synthesis, enhanced the interlobular and efferent arteriolar reactivity to the peptide among diabetic rats. Yet, after indomethacin treatment, the afferent and efferent arterioles of diabetic rats were still less reactive than control arterioles to Ang II. CONCLUSIONS: We conclude that the blunted reactivity of afferent and efferent arterioles to Ang II among diabetic hydronephotic kidneys cannot be fully explained by the influence of renal vascular-derived dilator prostaglandins.

Preglomerular and postglomerular blood flow: relationship to kidney disease and treatment.

BACKGROUND: In the kidney, the afferent and efferent arterioles normally constrict or dilate in response to changes in systemic blood pressure to maintain glomerular filtration while protecting the glomerulus from excessive pressure. In diabetes mellitus and hypertension, the two most common causes of kidney failure, sustained hypertension within the glomerulus damages the glomerular membrane and eventually results in loss of kidney function. SUMMARY: Techniques developed in the last 10 years allow direct study of the glomerulus and the glomerular circulation. In both diabetes and hypertension, the afferent vessels may dilate, resulting in excessive pressure in the glomerulus. Calcium antagonists, angiotensin-converting enzyme inhibitors, and cyclosporine have direct effects on the preglomerular and postglomerular vessels, and the afferent and efferent arterioles may respond differently to the same agent. CONCLUSIONS: Techniques for studying afferent and efferent arteriolar changes and glomerular filtration rate may provide important insights into the actions of drugs and into renal diseases. Clinicians are beginning to be able to select drugs that have desired effects on the renal microcirculation.

Contrasting effects of vecuronium and succinylcholine on the renal microcirculation in rodents.

We assessed the effects of succinylcholine and vecuronium on renal function and on the renal microcirculation in a rodent model. Vecuronium (0.02 mg/kg followed by 0.2 mg.kg-1 x h-1) caused a significant decrease of 16.1% +/- 3.87% in inulin clearance from 0.92 +/- 0.07 to 0.71 +/- 0.05 mL.min-1 x gKW-1 (gram of kidney weight), and a decrease in para-aminohippuric acid clearance by 21.6% +/- 4.69% from 1.58 +/- 0.26 to 1.31 +/- 0.20 mL.min-1 x gKW-1 (P < 0.05), whereas succinylcholine (0.45 mg/kg followed by 2 mg.kg-1 x h-1) altered neither. The effect of these muscle relaxants was also determined on the renal microcirculation in separate experiments using videomicroscopy. Succinylcholine (n = 10; 10(-10) to 10(-6) M) and its parent compound, acetylcholine (n = 10, 10(-10) to 10(-6) M) used as a control, caused a significant vasodilation from baseline diameter in the interlobular, afferent, and efferent arterioles. The vasodilation caused by succinylcholine was significantly less than that observed with acetylcholine. Atropine blocked the response to succinylcholine, indicating the latter has a muscarinic effect. In contrast, vecuronium caused a significant, selective vasoconstriction from baseline diameter in the preglomerular vessels, but not in the postglomerular vessels. The vasoconstriction caused by vecuronium was significantly different than the vasodilation caused by succinylcholine. The preglomerular vasoconstriction observed with vecuronium may contribute to the decrease in renal plasma flow and glomerular filtration rate observed experimentally. The choice of a neuromuscular blocking drug can therefore have the potential to influence renal function by altering the renal microcirculation.