[Effects of atorvastatin on ischemic acute renal failure in aging rats]. / Effetti della atorvastatina nell'insufficienza renale acuta ischemica del ratto anziano.

BACKGROUND: Aging (O) rats have a greater susceptibility to renal ischemia than young (Y) rats due to an endothelial dysfunction partially reversed by exogenous administration of L-Arginine. Since statins are able to increase nitric oxide (NO) production, aim of the study was to evaluate whether pre-treatment with atorvastatin (ATO, 10 mg/kg/day for 12 days), had positive effects on ischemic acute renal failure (ARF) of aging rats. METHODS: Renal clearance studies (inulin) were performed 24 hours after ischemia in 6 Groups (n=6 in each Group) of both Y- and O-rats: control rats (CON), untreated rats with ARF (Groups IRA), and rats with ARF but pretreated with ATO (Groups ATO+IRA). RESULTS: Renal ischemia determined a sharper decrease in GFR of Group O-IRA than Y-IRA (-80% and -63% vs respective CON, both p<0.001). In both Groups the fall in GFR was secondary to renal vasoconstriction and the consequent reduction in renal plasma flow. Pre-treatment with ATO did not modify GFR in Group Y-ATO+IRA, but was able to determine a marked rise in GFR of rats of O-ATO+IRA Group (+100% vs O-IRA), through a reduction in renal vascular resistances. Induction of ARF greatly enhanced nitrate excretion in Group Y-IRA, but slightly affected Group O-ARF. Administration of ATO did not modify nitrite excretion in Y rats, whereas it was able to increase nitrate excretion in O-ATO+ARF rats (+111% vs O-IRA). CONCLUSIONS: Pre-treatment with ATO is able to improve the renal response to ischemia in aging rats, through a mechanism which likely is NO-dependent.

[Progression of chronic renal failure in remnant rats: role of arginase inhibition]. / Progressione dell'insufficienza renale cronica nel ratto remnant: ruolo della inibizione dell'arginasi.

BACKGROUND: Oral administration of arginine to remnant (REM) rats (5/6 nx) slows the progression of chronic renal failure through a nitric-oxide(NO)-dependent mechanism. We have recently shown that inhibition of arginase, the main metabolic pathway of arginine, was able to induce similar results on renal dynamics (GIN: 2001, 18:285-290). Aim of the present study was to test whether these changes were mediated by increased availability of arginine-derived NO. Methods. Three Groups of REM rats were studied for 8 weeks after surgery: 1) untreated REM (Group REM); 2) REM rats treated with arginine (1%) in tap water (Group ARG); 3) REM rats administered a Mn++-free diet, to induce partial inhibition of arginase (Group MNF). Normal unmanipulated rats were used as controls (Group NOR). RESULTS: Liver arginase activity was significantly depressed only in MNF-rats (-35% vs. REM, p < 0.01). Blood pressure was significantly lower in Group MNF vs. ARG and REM after 6 weeks (p < 0.05). Proteinuria was significantly decreased in Group ARG (-42%, p < 0.05 vs. REM) and even more in Group MNF (-57%, p < 0.01). ARG plasma levels, decreased in REM rats (-41% vs. Group CON), were normalized in Group ARG (p < 0.01 vs. Group REM); arginase inhibition was able to increase such levels in Group MNF (+38% vs. REM) and this resulted in a proportional rise in urinary nitrite excretion (+33% vs. REM), grossly depressed in REM rats. Renal arginase activity was lower in all the Groups of remnant rats vs. Group NOR, but intrarenal concentrations of ARG were significantly lower only in rats of Group MNF (p < 0.05 vs. all the other Groups). Histological examination showed that MNF-rats had a glomerular sclerosis index lower than in the other Groups (p < 0.05 vs. Group REM and ARG). CONCLUSIONS: In conclusion, inhibition of arginase in remnant rats slows the progression of CRF and preserves renal histology through a direct and/or indirect NO-dependent mechanism.

Acute effects of rapamycin on glomerular dynamics: a micropuncture study in the rat.

The acute effects of cyclosporin (CsA, 20 mg(kg i.v.) and rapamycin (RAPA, 5 mg(kg i.v.) on glomerular dynamics were separately investigated by renal micropuncture in two groups of intact rats (group CsA and RAPA, respectively) and compared with vehicle-treated rats, used as controls (group CON). Left kidney glomerular filtration rate (GFR) was decreased by CSA (-35% vs. CON, P<0.05), but was not affected by RAPA (-14% vs. CON, NS), whereas the single-nephron GFR (SNGFR) was significantly decreased in both groups (-40% in CsA, P<0.01 and -26% in RAPA, P<0.05 vs. CON). In both groups glomerular plasma flow (GPF) was significantly reduced vs. CON (CsA: -48%, and RAPA: -25%) due to the increase in both afferent (Ra) and efferent (Re) glomerular resistances: group CSA showed a prevalent rise in Re (+98% vs. CON, P<0.001) than in Ra (+66%, P<0.001); in group RAPA the increment was modest and similar in Ra and Re (+33 and +32%, respectively, NS versus CON). A further group of rats was studied in which L-Arginine (ARG), the precursor of nitric oxide (NO), was administered (2.5 mg/Kg/min iv) with RAPA (group ARG). ARG limited the rise in Ra and Re, thereby preserving GPF; nevertheless, SNGFR remained low (-26% vs. CON, P<0.05) due to the decrease in the effective filtration pressure (-26% vs. CON). These data demonstrate that: (1) CsA is nephrotoxic at immunosuppressive doses; (2) RAPA, even at huge doses, has marginal effects on renal and glomerular dynamics; (3) the ARG-NO pathway is only partially involved in the vasoconstriction of superficial nephrons after RAPA administration.

The impact of early normalization of haematocrit by erythropoietin on renal damage in the remnant kidney model.

BACKGROUND: Correction of anaemia in moderate to advanced renal failure is still a matter of debate because of postulated detrimental effects of erythropoietin on the progression of renal damage. METHODS: The renal effects of early normalization of haematocrit (Htc) by erythropoietin (rHuEpo) were investigated from the time of 5/6 nephrectomy up to 8 weeks post-intervention in three groups of remnant kidney model rats: untreated controls (CON), rats receiving 100 UI/kg body-wt of rHuEpo i.p. twice a week (EPO), and rats receiving rHuEpo in which periodic phlebotomies maintained Htc similar to the value of the control group (PHL). The latter group was included to evaluate the direct effects of rHuEpo on renal damage, i.e. independent from Htc correction. RESULTS: Two weeks after renal ablation (basal), Htc decreased in CON and PHL rats (from 49.3+/-1.4% to 43.2+/- 1.1, P < 0.05 and from 49.6+/-1.1 to 43.3+/-1.5%, P<0.05 respectively), while it remained consistently normal in EPO rats (48.9+/-1.2% to 48.9+/-1.50/%, P<0.05 vs other groups). Thereafter Htc did not change throughout the remaining period in all groups. At the end of the study, with respect to basal, resting blood pressure increased significantly by the same extent in CON (+ 13+/-2%) and EPO rats (+ 15+/-5%), while it remained constant in PHL rats. Notably, creatinine clearance significantly decreased in CON (-53+/-8% 8 vs basal) and EPO (-38+/-8% vs basal), while it did not change in PHL rats. Likewise the degree of proteinuria as well as renal morphologic alterations and glomerular hypertrophy/sclerosis was similar in CON and EPO rats, and was significantly more severe than in the phlebotomized group. The only difference detected between CON and EPO group was the greater mesangial hypercellularity in rHuEpo-treated rats. CONCLUSION: In uraemic rats, chronic treatment with rHuEpo aimed at normalization of Htc beginning the early stage of renal failure does not inevitably account for a rise in systemic blood pressure. In addition, neither erythropoietin per se nor the correction of haematocrit accelerates the progression of renal damage when blood pressure remains constant.

Serial morphometric analysis of sclerotic lesions in primary "focal" segmental glomerulosclerosis.

The possibility of missing the diagnosis of focal segmental glomerulosclerosis (FSGS) has been primarily attributed to the focal distribution of the sclerotic lesions, but this assumption has not been verified by any serial morphometric analysis of renal biopsy specimens. The aim of this study is to assess the size and the distribution of sclerotic lesions in primary FSGS and to establish the minimum number of glomeruli and sections necessary for the diagnosis. Fourteen biopsies from adult nephrotic patients with primary FSGS were carefully selected from a group of 41 biopsies, to minimize the possibility of finding and misinterpreting nonspecific glomerular scars, and were serially cut to obtain 1485 consecutive 2 microns-thick sections that, after PAS staining, showed 182 glomeruli. Fifty-seven glomeruli were "complete", i.e., they emerged after the first section and disappeared before the last section. The percentage of glomeruli with sclerotic lesions was 31.5% in the starting section, 71.8% after the observation of all serial sections, and 81.7% when only the complete glomeruli were considered. The morphometric analysis on complete glomeruli revealed that the volume of the sclerotic lesions averaged just 12.5% +/- 2.2 SE of the entire glomerular volume, and the statistical analysis revealed that the minimum number of glomeruli needed in the starting section to exclude sclerotic lesions is eight (P < 0.01) or nine (P < 0.001). If fewer glomeruli are seen, it is necessary to cut 2 microns-thick serial sections, but to examine just one of every 11 (P < 0.001), the number of sections to examine being proportional to the number of glomeruli found. In conclusion, this study shows that the distribution of sclerotic lesions in primary FSGS is not focal, but diffuse; however, because of the small size of the sclerotic lesions, the probability of missing the diagnosis is statistically relevant when fewer than eight glomeruli are found in the starting section, unless a serial morphological analysis, even on a reduced number of sections, is made.

Functional versus structural changes in the pathophysiology of acute ischemic renal failure in aging rats.

The aim of this study was to gain further insight into the greater susceptibility to acute ischemic renal failure (ARF, 30 min of renal arteries clamping) of old rats (O, 18 months) as against young rats (Y, 3 months). All the rats ate a hypoproteic diet (14% of casein) to avoid age-related glomerulosclerosis in O. Basal renal dynamics was similar in O and Y (Groups CON). One day after ARF, the decrease in GFR was more severe in O than in Y (-82% and -57% vs. respective CON, P < 0.05), due to a greater rise of RVR in O (+258%) than in Y (+104%). The histological renal damage after ischemia was comparable in the two groups with ARF. Five days after ARF, the recovery of renal function was characterized by a slower rise of GFR in O than in Y. In two further groups, two different scavengers of oxygen-free radicals, dimethylthiourea (DMTU) and superoxide dismutase (SOD), were administered at the time of arterial occlusion. DMTU had protective effects in Y but not in O (delta GFR was -28% and -72%, respectively); in contrast, SOD was more effective in O (delta GFR = -58%) than in Y rats (delta GFR = -40%). To test the hypothesis that such a difference was related to the capacity of SOD to increase the levels of nitric oxide (NO), four more groups of Y and O rats were pretreated with L-arginine (ARG), precursor of NO, in tap water (1.5%). No difference in renal dynamics was detected in basal conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Early glycosylation products induce glomerular hyperfiltration in normal rats.

The effects of early glycosylation products (Amadori Products, AP) were investigated in male Munich-Wistar rats to establish whether AP play a role in the pathogenesis of glomerular hyperfiltration of early diabetic nephropathy. To mimic such a condition, normal rats were transfused with blood containing in vitro glycated serum (Group GLYC) to achieve plasma levels of Amadori products similar to those measured in rats with streptozotocin-induced diabetes. Rats transfused with normal blood were used as control (Group CON). Glomerular hemodynamics was evaluated in basal condition (B) and during acute hyperglycemia (HG). Blood transfusion did not alter basal hemodynamics. In Group CON, HG determined a rise of single nephron GFR (41.4 +/- 3.2 vs. 32.1 +/- 1.8 nl/min, P less than 0.005), secondary to the increase of afferent effective filtration pressure (EFPa, +19% vs. B, P less than 0.01). Rats of Group GLYC, in B, had values of SNGFR higher than those of Group CON B (46.8 +/- 3 nl/min, P less than 0.05, ANOVA). This increase was mediated by a significant reduction of glomerular afferent arteriole (Ra, -38% vs. Group CON B, P less than 0.05), a rise in hydrostatic gradient pressure in glomerular capillaries (delta P, +17%, P less than 0.05) and of EFPa (+31%, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Medium-term cyclosporin renal dysfunction and its reversibility in rats.

Renal dynamics and morphology were investigated by metabolic, renal micropuncture (RM), and electron microscopy (EM) studies in 50 female rats treated with cyclosporin A (CsA, 40 mg.kg body wt-1.48 h-1) for either 10, 20, or 30 days (groups CsA 10, CsA 20, and CsA 30, respectively); control rats received olive oil (group N). Body weight gain, sodium metabolism, and plasma volume were not altered by CsA administration in any group. GFR was decreased in group CsA 10 vs. group N (-10%, P less than 0.05) and was further impaired in groups CsA 20 and CsA 30 (-45%, P less than 0.01 vs. group N). RM studies showed a significant decrease of single-nephron glomerular filtration rate (SNGFR) in group CsA 30 vs. group N (-26%, P less than 0.01) after the fall of glomerular capillary pressure (Pgc;-8%, P less than 0.05), the increase of afferent arteriole resistance (Ra; +40%, P less than 0.05), and the consequent decrease of glomerular plasma flow (GPF; -28%, P less than 0.05). Thirty days after CsA withdrawal, SNGFR returned to normal values (P less than 0.01 vs. group CsA) as a result of the normalization of Pgc, Ra, and GPF.EM showed only a progressive vacuolation of proximal and distal tubular cells. These data suggest that medium-term administration of CsA is associated with reversible changes in glomerular dynamics and only mild histological lesions.

Role of atrial natriuretic factor in renal adaptation to variation of salt intake in humans.

This study was performed to define the extent to which atrial natriuretic factor (ANF) contributes to upregulate salt excretion in subjects eating a high-salt diet. Eight normal volunteers were first studied at low-salt diet (80 mmol NaCl/day); urinary sodium excretion (UNaV) and plasma ANF (PANF) were measured in the basal condition and during stepwise infusion of human alpha-ANF at 2, 4, 8, and 16 ng.min-1.kg-1. Then the same subjects were shifted to a high-salt diet (400 mmol/day), and UNaV and PANF were measured in the new balance condition. At low-salt diet, UNaV averaged 0.069 meq/min, and PANF averaged 21 pg/ml; infusion of human alpha-ANF raised stepwise both UNaV and PANF (means in meq/min and pg/ml, respectively, were 0.177 and 46, 0.218 and 76, 0.360 and 86, and 0.601 and 182). Infusion of ANF caused a progressive fall of plasma aldosterone and plasma renin activity. Mean UNaV and PANF at high-salt diet were 0.301 meq/min and 35 pg/ml. Thus, by increasing experimentally PANF in a low-salt diet condition to the levels occurring physiologically in a high-salt diet condition, a significant rise in UNaV is evoked, which accounts for approximately 50% of the rise of UNaV that is necessary to balance the increased salt intake.

Absence of acute nephrotoxicity with low doses of cyclosporin: experimental study in the rat.

No study has, to our knowledge, evaluated the acute effects of low immunosuppressive doses of cyclosporin (CsA) on renal function. To establish whether a relationship exists between the dosage of CsA and the onset of nephrotoxicity, 28 rats were studied by renal clearances before (control) and after i.v. administration of different doses of CsA: 3 mg/kg b.w. (group 1); 7 mg/kg b.w. (group 2); 11 mg/kg b.w. (group 3); 15 mg/kg b.w. (group 4). No change in renal function was observed between control and the post-CsA period in groups 1 and 2. GFR (inulin clearance) was decreased vs the control period in group 3 and group 4 (-22% and -37%, respectively, P less than 0.001); the difference between these two groups was statistically significant (P less than 0.01). Effective renal plasma flow (PAH clearance) was similarly decreased in groups 3 and 4 vs their control periods (-21% and -28%, respectively, P less than 0.001) due to the increase of total renal vascular resistance (+41% and +42%, respectively, P less than 0.001). Filtration fraction was significantly decreased by CsA in group 4 (P less than 0.01 vs the control period). PAH renal extraction, urinary volume, and sodium and potassium excretion were similar in all groups before and after CsA. PRA and ADH were significantly increased only in group 4 (P less than 0.01) vs the baseline values. A high and significant relationship was detected between CsA dosage and the decrease of GFR (r = 0.81, P less than 0.001) and RPF (r = 0.612, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Glomerular dynamics and salt balance in pregnant rats with renal hypertension.

These studies were aimed at investigating whether chronic hypertension in pregnancy causes changes both in salt excretion (NaE) and in glomerular hemodynamics. Metabolic and renal micropuncture studies were performed in pregnant (P) and Virgin (V) Munich-Wistar rats with normal blood pressure (N) and two-kidney Goldblatt hypertension (H). Mean NaE was higher in PN than VN (2.7 vs. 1.7 meq/day, P less than 0.01). Hypertension raised NaE both in P and V rats: in P and V rats with "benign" hypertension (blood pressure less than 180 mmHg) NaE averaged 3.2 and 2.6 meq/day, respectively (P less than 0.05); mean NaE was 5.9 and 3.8 meq/day, respectively (P less than 0.01), in P and V rats with "malignant" hypertension (blood pressure greater than or equal to 180 mmHg). Afferent arteriole resistance (Ra) averaged 1.73 and 3.50 10 dyn.s-1.cm5 in PN and VN, respectively (P less than 0.01). Hypertension raised Ra in V, but not in P rats (4.47 vs. 2.14 10 dyn.s-1.cm5, P less than 0.01). Thus glomerular plasma flow, glomerular capillary hydrostatic pressure, and single-nephron glomerular filtration rate were markedly higher in PH than VH rats: in PH rats single-nephron filtration fraction was significantly lower than in VH. These results show that in PH rats a marked rise in NaE is associated with glomerular vasodilation.

Reversibility of acute cyclosporin nephrotoxicity by dopamine. Micropuncture study in the rat.

The ability of dopamine to neutralise the effects acutely induced by cyclosporin (CsA) on glomerular dynamics was evaluated in four groups of female Munich-Wistar rats, prepared for micropuncture: group I (n = 9), normal rats receiving saline as placebo; group II (n = 10), rats treated with CsA (20 mg/kg b.w. in 1 h); group III (n = 8) rats treated with CsA, as in group II, and then with vasodilating doses of dopamine (1.2-2.0 micrograms/100 g b.w./min in continuous intravenous infusion); group IV (n = 7), rats administered Cremophore EL, the vehicle of CsA, in corresponding doses. Single nephron GFR (SNGFR), glomerular plasma flow (GPF), afferent and efferent arteriole resistances (Ra and Re, respectively), SN filtration fraction (SNFF), ultrafiltration coefficient (Kf) were measured. Body weight, blood pressure and haematocrit were similar in the four groups. GFR was significantly reduced in group II (0.83 +/- 0.08 ml/min vs 1.29 +/- 0.01 in group I, 1.46 +/- 0.25 in group III, and 1.40 +/- 0.09 in group IV, P less than 0.05 vs all the groups), while no statistical difference was detected in urinary volume. SNGFR was significantly reduced in group II vs group I (18.7 +/- 1.8 nl/min vs 30.6 +/- 1.3, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Renal function in pregnant rats with two-kidney goldblatt hypertension.

This study was carried out in female Wistar-Münich rats with two-kidney, one-clip hypertension, using clipped normotensive rats as controls. Metabolic studies were performed in the first two weeks of pregnancy, consisting of daily measurement of systolic blood pressure (BP) (tail-cuff), body weight (BW), and salt and water balance. At the end of metabolic studies, glomerular dynamics were studied in the unclipped kidney by micropuncture. During pregnancy, urinary output of Na+ and water was greater in hypertensive than normotensive rats. The greater natriuresis accounted for a reduced Na+ retention and a lower increase in maternal BW. Micropuncture studies showed an impaired renal auto-regulation. These results show that hypertension in pregnancy causes a salt-losing tendency, that may be secondary to incomplete renal autoregulation.

Effects of pregnancy on glomerular dynamics: micropuncture study in the rat.

Glomerular dynamics were investigated by micropuncture in 15-day pregnant Munich-Wistar rats. Female non-pregnant rats were used as control. In hydropenia, single nephron glomerular filtration rate (SNGFR) averaged 37.2 nl/min/g kidney weight in pregnant rats, and 26.2 nl/min/g kidney weight in controls (P less than 0.0005). During pregnancy, mean glomerular plasma flow (GPF) rose from 63.0 to 104.5 nl/min (P less than 0.0005), and glomerular capillary hydrostatic pressure (PG) from 44.8 to 50.6 mm Hg (P less than 0.0005). This rise in PG accounted for an increase in effective filtration pressure (EFP). Mean EFP at the efferent end of the glomerulus rose from near zero to 9.7 mm Hg, indicating filtration pressure disequilibrium. After extracellular fluid volume expansion with saline, GPF and EFP were still greater during pregnancy. A filtration pressure disequilibrium occurred also in non-pregnant rats, allowing calculation of definite values of the ultrafiltration coefficient (Kf). During pregnancy, mean Kf was reduced from 0.0332 to 0.0285 nl/(sec X mm Hg) (P less than 0.005). SNGFR was moderately, but not significantly, increased. These results show that during pregnancy glomerular dynamics is characterized by a rise in GPF and EFP, and by a reduction in Kf. Following these changes, a plasma-flow dependent rise in SNGFR occurs in hydropenia. After expansion, instead, SNGFR is unmodified because the dependence of ultrafiltration on plasma-flow declines while the influence of Kf increases at high values of GPF.