Nicholas T. Stowe

The use of the endothelin receptor antagonist, tezosentan, before or after renal ischemia protects renal function

Background. Utilization of organs subjected to ischemia/reperfusion (I/R) injury could expand the donor pool. Endothelin (ET) is implicated in renal I/R injury. Therefore, our study compared the effectiveness of pre- and postischemic administration of the ET receptor antagonist, Tezosentan, in preserving renal function. Methods. In a rat model, a kidney was subjected to 45 min of ischemia along with a contralateral nephrectomy. After 24 hr of reperfusion, renal function was assessed by serum creatinine (Scr), inulin clearance (glomerular filtration rate; GFR), and histology. ET-1 peptide expression was localized using immunohistochemistry. Three groups were studied: I/R untreated (n=17), I/R pretreated (n=11), and I/R posttreated (n=13) with Tezosentan (15 mg/kg, i.v.). Results. Tezosentan significantly decreased ( P <0.05) the rise in Scr from I/R injury (2.0±0.4 mg/dl, before and 2.9±0.4 mg/dl, after treatment) compared with untreated animals (4.2±0.4 mg/dl). GFR was significantly increased ( P <0.05) from 0.13±0.03 ml/min (untreated animals) to 0.74±0.16 and 0.47±0.14 ml/min (pre- and posttreated animals). Untreated animals had significant cortical acute tubular necrosis, which was almost completely prevented by pretreatment with Tezosentan and markedly reduced by posttreatment. Increased ET-1 peptide expression was noted in the renal vasculature and in the cortical tubular epithelium of kidneys exposed to I/R. Conclusions. The purpose of this study was to optimize the function of kidneys exposed to I/R injury. Pretreatment as well as posttreatment with Tezosentan successfully decreased Scr, increased GFR, and maintained renal architecture in kidneys after ischemia. Therefore, ET receptor antagonists may be useful to preserve renal function in the transplantation setting.

Pretransplant assessment of renal viability by phosphorus-31 magnetic resonance spectroscopy. Clinical experience in 40 recipient patients.

A group of 40 cadaveric kidneys was studied just prior to planned transplantation to further assess the applicability of 31P-MRS in the analysis of clinical renal transplant viability. Renal intracellular high-energy phosphorus metabolites (ATP [or NADP], phosphomonoester [PME] and inorganic phosphate [Pi]) and pH were measured noninvasively with MRS surface coils external to cold storage containers. Pretransplant MRS parameters were correlated with subsequent renal function in recipient patients (measured one week postoperatively by the need of dialysis, drop in serum creatinine, urine output, and 123I or 131I Hippuran assessed renal tubular function). ATP and NADP was detected in eleven kidneys and was significantly (P<0.001) associated with the best renal function posttransplantation. These kidneys also had the highest PME/Pi ratios (1.66–0.54), while lower ratios (0.36–0.10) were associated with prolonged acute tubular necrosis. The PME/Pi ratios significantly (P<0.0001) correlated with subsequent clinical renal function, whereas cold storage times (37±10 hr) or intracellular renal pH (6.53–7.91) did not. These preliminary data suggest that MRS is a noninvasive, nondestructive and sterile method for assessing clinical viability during hypothermic storage of human cadaver kidneys and the subsequent recovery of renal function postrenal transplantation.

Effects of furosemide versus isolated ultrafiltration on extravascular lung water in oleic acid-induced pulmonary edema

We studied the effects of no treatment, furosemide treatment, and isolated ultrafiltration on extravascular lung water (ETV1.) in mongrel dogs in whom pulmonary edema was induced with oleic acid. In all treatment groups, ETV1. was significantly elevated 90 min after oleic acid infusion. At 270 min, we found no difference between nontreatment and furosemide. There was, however, a significant difference between no treatment and ultrafiltration but not between furosemide and ultrafiltration. In spite of observations which suggest that ultrafiltration is of benefit in reducing ETVL, we could not demonstrate superiority of one therapy over another.

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. Lovastatins direct renal protective effect seems to be independent of its lipid-lowering properties.

Treatment of acute focal cerebral ischemia with propranolol.

Propranolol has been found to have a protective effect in experimental myocardial ischemia. Protection of ischemic kidneys was subsequently demonstrated following treatment with propranolol and its weaker beta blocking isomer, d-propranolol. The objective of the present investigation was to study the effects of propranolol (i.e., racemic d,1 mixture) and d-propranolol upon regional cerebral blood flow (rCBF) and early ischemic changes following experimental middle cerebral artery (MCA) occlusion. Thirty adult cats, lightly anesthetized with ketamine hydrochloride, underwent 3 hours or right MCA occlusion. Ten cats were untreated. Ten cats were given a continuous infusion of propranolol (1 mg/kg/hr) for 4 hours beginning 1 hour before MCA occlusion and a 4 mg/kg bolus immediately before occlusion. Ten cats were given a continuous infusion of d-propranolol (0.5 mg/kg/hr) for 4 hours beginning 1 hour before MCA occlusion and a 2 mg/kg bolus immediately before occlusion. The therapeutic agents were injected directly into the right carotid artery. The rCBF in the right Sylvian region was not significantly different in the 3 groups. EEG changes also were similar. Carbon filling defects were found to be smallest in the d-propranolol-treated group. Light microscopic studies demonstrated a reduction in infarct size in the propranolol and d-propranolol groups. The findings of the investigation indicated that propranolol and d-propranolol do not have a deleterious effect on rCBF after MCA occlusion and suggested that these agents have a protective effect upon ischemic cerebral tissue.

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. Lovastatins 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.

The combination of lovastatin and enalapril in a model of progressive renal disease.

Puromycin-induced nephrotic syndrome is an animal model of progressive renal disease. Both angiotensin converting enzyme inhibitors and lipid-lowering agents have been used to preserve renal structure and function in this model, although neither completely prevents progression. We tested the hypothesis that the combination of the two agents would be more protective than either alone. Rats were divided into five groups; all were uninephrectomized. Four groups were given puromycin at a dose of 10 mg/100 g body weight (BW) with additional doses of 4 mg/100 g BW given intraperitoneally at 4, 5, and 6 weeks thereafter. One group was given enalapril (EN) 50 mg/l dissolved in the drinking water; the second received lovastatin (L) 15 mg/kg given daily by gavage; the third received both agents; the fourth was left untreated, and the final group received no puromycin and served as the control group. Eight weeks after the initial dose of puromycin, glomerular filtration rate (GFR), as inulin clearance, and protein excretion were determined and blood was collected for cholesterol and triglycerides. Blood pressure was not different between any of the groups. At the end of the study period, serum cholesterol [mean ±SD, 252±185 mg/dl (L), 135±101 mg/dl (L+EN)] and triglycerides (239±200, 148±158 mg/dl) were significantly lower (P<0.001) in the lovastatintreated groups than in the untreated puromycin group (535±255 mg/dl and 579±561 mg/dl, cholesterol and triglyceride, respectively). Likewise protein excretion was significantly lower (P<0.001) in these groups also [507±336 (L), 253±331 (L+EN) vs. 745±381 (puromycin) mg/24 h]. Renal function was also preserved with a significantly better GFR per gram kidney weight in the lovastatin-treated groups [0.56±0.33 (L), 0.54±0.19 (L+EN) vs. 0.17±0.11 ml/min per gram]. Glomerulosclerosis, as measured by a sclerotic index, was also significantly less in the lovastatin plus enalapril-trated group (0.29±0.35) compared with the untreated puromycin group (2.29±0.54). Although enalapril had little effect by itself, the combination of enalapril and lovastatin appeared to significantly improve the decrease in serum cholesterol, triglyceride, and protein excretion. Thus treatment with lovastatin alone, and its subsequent lowering of serum cholesterol and triglyceride concentrations, improved renal structure and function in this model of puromycin nephrosis. The combination of lovastatin and enalapril resulted in the least histological damage, the least protein excretion, and preservation of GFR.

Renal Vascular Response to Vasodilators Following Warm Ischemia and Cold Storage Preservation in Dog Kidneys

The purpose of this study was to determine whether warm ischemia (WIT) and cold storage preservation (CSP) impair endothelium-dependent vascular relaxation in the kidney. Twenty-four canine kidneys were harvested, preserved with CSP for 24 or 48 hours, and then perfused with canine blood at 37 C for the determination of glomerular filtration rate (GFR), perfusion flow rate, and renal vascular resistance (RVR). There were four experimental groups: Group I--no WIT followed by 24 hours CSP, Group II--30 minutes WIT followed by 24 hours CSP, Group III--no WIT followed by 48 hours CSP, Group IV--30 minutes WIT followed by 48 hours CSP. Endothelial function in each group was evaluated using acetylcholine (ACh, 1 mg. bolus) as an endothelial dependent vasodilator, and sodium nitroprusside (NP, 10 mg. bolus) as an endothelial independent vasodilator. Glomerular filtration rate was significantly less (P < .05) and RVR was significantly greater (P < .05) for kidneys from Groups II, III and IV compared to group I. The highest RVR was observed in kidneys from Groups II and IV. Nitroprusside administration caused an equivalent reduction in RVR among all four study groups. ACh administration caused a similar reduction in RVR in Groups I and III; however, the change in RVR was significantly less in Groups II and IV (P < .05). We hypothesize that the more severe ischemic insult in the latter groups led to vascular endothelial damage with a consequent loss of ability to secrete endothelium-derived relaxing factor in response to ACh administration.

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.

Treatment of acute focal cerebral ischemia and recirculation with d-propranolol

The purpose of the investigation was to evaluate the effects of d-propranolol upon temporary cerebral ischemia followed by a period of reperfusion, that is, a situation analogous to major cerebral artery embolization. Twenty adult cats, lightly anesthesized with nitrous oxide, underwent 4 hours of right middle cerebral artery (MCA) occlusion and 2 hours of recirculation. Ten cats were untreated and 10 cats received d-propranolol, the weak beta-blocking isomer of racemic (d,l) propranolol. The d-propranolol was infused directly into the right carotid artery at doses of 2 mg/kg, given as a bolus immediately before MCA occlusion, and 0.33 mg/kg/hour, given continuously for 6 hours beginning immediately after MCA occlusion. Systemic arterial blood pressure was similar in both groups, but heart rate was transiently reduced in the treated group immediately after the bolus injection of d-propranolol and MCA occlusion. Regional cerebral blood flow (rCBF), measured by the xenon-133 clearance technique, was not significantly different in the ischemic, right hemisphere. Electroencephalographic (EEG) activity changes in the ischemic, right hemisphere were similar in both groups, but there was significant deterioration of EEG activity in the left, nonischemic hemisphere of untreated cats after MCA reopening. Swelling of the ischemic, right hemispheres was similar in both groups and more severe than in previous studies wherein there was no recirculation phase. Carbon perfusion and blood-brain barrier changes were also similar. The results of the study failed to show a protective effect despite theoretical beneficial actions of d-propranolol. Also, the study demonstrated that d-propranolol does not have a detrimental effect upon rCBF in acute focal cerebral ischemia.