L. Schramm

Role of L-Arginine-Derived NO in Ischemic Acute Renal Failure in the Rat

Nitric oxide (NO) is involved in the regulation of renal perfusion and glomerular hemodynamics under basal conditions. We examined the hypothesis that L-arginine-derived NO modifies ischemic acute renal failure (ARF) in the rat. After a basal period ischemia was induced by clamping of both renal arteries (40 min). Thereafter, in the reperfusion period, we intravenously infused L-arginine (Arg, 300 mg/kg/60 min), or L-monomethylarginine (MeArg, 30 mg/kg/60 min), or Arg + MeArg (300 mg/kg/60 min, 30 mg/kg/60 min, resp.). Besides monitoring of urinary flow rate and arterial blood pressure, and determination of sodium excretion, glomerular filtration rate (GFR, mL/min/100 g) was estimated at the end of the infusion period and again after another 30 and 120 min by inulin clearance (fluorescence-marked inulin). In the basal period GFR showed no differences between the groups (Arg: 0.86 +/- 0.07, MeArg: 0.92 +/- 0.06, Arg + MeArg: 0.89 +/- 0.08, control: 0.84 +/- 0.07). At 180 min after the beginning of the reperfusion period, GFR was 0.13-0.02 in the control group. After administration of Arg, a remarkable and persistent increase in GFR was observed (0.28 +/- 0.03), whereas infusion of MeArg showed no significant effects (0.13 +/- 0.04). Combined administration of Arg + MeArg revealed a moderate increase of GFR (0.19 +/- 0.05), ranging between the Arg and the control group. Also, 60 and 90 min after the beginning of the reperfusion period, the highest values for GFR were obtained in the Arg group. We conclude that in this model of ischemic ARF in the rat, L-arginine-derived NO is capable of improving renal function. These data underline the regulatory role of the L-Arg-NO pathway for renal function, not only under normal conditions, but also in ARF.

Toxic Acute Renal Failure in the Rat: Effects of Diltiazem and Urodilatin on Renal Function

Beneficial effects of natriuretic peptides have been reported in different models of acute renal failure (ARF). Calcium antagonists can also improve renal function, especially in ischemic models of ARF. The aim of our study was to investigate the effects of urodilatin and diltiazem alone and in combination in uranyl nitrate-induced toxic ARF in the rat. Three hours after induction of ARF glomerular filtration rate (GFR) was clearly diminished to about 50% compared to basal values. Intravenous infusion of diltiazem and urodilatin revealed a significant increase of GFR that even continued after cessation of drug delivery. Combined administration of urodilatin and diltiazem had no additional effect, probably due to a more pronounced fall in blood pressure in this group. Besides their vasorelaxing and blood pressure lowering effects both drugs also revealed diuretic activity. In conclusion both urodilatin and diltiazem are able to elevate GFR in the early phase of toxic ARF in the rat.

Dose-dependent stimulation/inhibition effects of cyclosporin A on lysosomal cathepsin activities in cultured proximal tubule cells

The effects of cyclosporin A on the activities of lysosomal cysteine proteinases (cathepsin B, H, L+B) in LLC-Pk1 cells were investigated to elucidate their potential role in cyclosporin A-induced nephrotoxicity. Cyclosporin A at lower doses (0.1–1,000 ng/ml) stimulated cathepsin B, H, L+B. In contrast, at a higher dose (10,000 ng/ml), it inhibited these proteinase activities associated with a reduction in protein degradation. In line with the altered proteinase activities, cellular protein content was decreased at the lower dose (10 ng/ml) and increased at the higher dose. The higher dose of cyclosporin A also enhanced cellular lipid peroxide content after an exposure of 4 and 10h. Co-incubation with superoxide dismutase (40 U/ml) did not ameliorate the inhibition of cathepsin B activity induced by the high dose of cyclosporin A. On the contrary, the calcium channel blocker verapamil (10−6 M) prevented this inhibition. In conclusion, cyclosporin A exerts a dose-dependent biphasic effect on lysosomal cysteine proteinase activities. A rise in cytosolic Ca2+ concentration, but not an enhanced lipid peroxidation, may be involved in the suppression of cathepsin B activity induced by the higher dose of cyclosporin A. These studies raise the possibility that alterations of tubular proteinase activity may play a role in the cyclosporin A-induced nephrotoxicity.

Effects of Urodilatin and Diltiazem on Renal Function in Ischemic Acute Renal Failure in the Rat

In humans as well as in experimental models the hallmark of ischemic acute renal failure (ARF) is a profound diminution in glomerular filtration rate (GFR) and renal blood flow. Both calcium antagonists and a-ANP have been reported to exert beneficial effects in ischemic ARF. No data, however, exist about combined administration of the natriuretic peptide urodilatin and calcium channel blockers. We therefore investigated the effects of urodilatin (URO, 40 micrograms/kg/h, i.v.) and diltiazem (DIL, 300 micrograms/kg/h, i.v.) in the rat given immediately after clamping of both renal arteries for 40 min. Compared to controls (0.07 +/- 0.01) depressed GFR (ml/min/100 g) was clearly elevated with URO (0.16 +/- 0.03), DIL (0.13 +/- 0.03) and URO + DIL (0.14 +/- 0.02) after the ischemic lesion. After cessation of drug delivery the beneficial effects were blunted in the URO group, in contrast to the DIL and URO + DIL group, where GFR was significantly elevated compared to controls even 3 h after starting reperfusion. Besides that also urine flow, sodium excretion and blood pressure were examined. In conclusion both URO and DIL exert beneficial effects in ischemic ARF in the rat while infused. In contrast to URO DIL showed prolonged beneficial effects even after cessation of drug delivery. An additional effect of both drugs could not be observed.

Insulin-Like Growth Factor I Induced Reduction in Cysteine Proteinase Activity in Freshly Isolated Proximal Tubule Cells of the Rat

The potential effects of insulin-like growth factor I (IGF-I) on lysosomal cysteine proteinases (cathepsin B, H and L+B activities) were investigated in the freshly isolated proximal tubule cells of rats. IGF-I significantly inhibited these enzyme activities after an incubation time of 80 min. This effect was associated with a dose-dependent increase in cellular protein content. The study suggests that, besides the established enhanced protein synthesis, IGF-I-induced cellular hypertrophy is mediated by a suppression of the proteolytic enzyme activity in proximal tubular cells.

Atrial natriuretic peptide and verapamil can prevent gentamicin induced acute renal failure in the rat

Summary: Calcium channel blockers are able to improve renal function in acute renal failure (ARF) and natriuretic peptides can also exert beneficial effects. At present it is unknown whether administration of atrial natriuretic peptide (ANP) and a calcium channel blocker given before a toxic lesion can prevent gentamicin induced ARF. the mechanisms of action of natriuretic peptides and calcium channel blockers are different and, as yet, it has not been clarified if combined administration can augment the effects on renal function. After a basal period we investigated the effects of verapamil (VER, 0.66 mg/kg), ANP, (30 μg/kg) and a combination of both (identical doses as described individually). the drugs were given intravenously for a period of 40 min (infusion period) before gentamicin (15 mg/kg, i.v.) was administered for induction of ARF. Basal values for glomerular filtration rate (GFR, mL/min) were around 1.8 with no differences between the groups. At the end of the infusion period (before application of gentamicin) GFR was significantly elevated with VER + ANP (3.13 ± 0.51), ANP (2.70 ± 0.59) and VER (2.34 ± 0.47) compared to controls (saline, 1.7 ± 0.48). After application of gentamicin GFR significantly dropped in the control group (0.77 ± 0.21, 0.75 ± 0.19, respectively), indicating development of ARF. In contrast with VER + ANP, ANP and VER GFR could be maintained for 30 min (2.47 ± 0.39, 2.28 ± 0.33, 2.22 ± 0.43, respectively) and 130 min (2.11 ± 0.32, 1.86 ± 0.29, 2.11 ± 0.28, respectively) after gentamicin. Moreover ANP and VER revealed natriuretic activity and, due to their vasorelaxing potency, also influenced arterial blood pressure. We conclude that both VER and ANP are able to prevent early gentamicin induced ARF when given before the toxic lesion. Both drugs induce hyperfiltration while infused, in particular when administered in combination.