Nitrogen balance in adult female mink (Mustela vision) in response to normal feeding and short-term fasting

Ten adult female mink (Mustela vison) were studied in a 7 d balance experiment consisting of a 2 d pre-surgery feeding period, followed by surgery, 1 d of recovery 4 d of ad libitum feeding, and a 2 d fasting period. In this experiment (Expt A) the animals had osmotic pumps implanted for continuous release of radioactively-labelled p-aminohippuric acid (p-aminobenzoyl-2-[3H]glycine; [3H]PAH; n 10) and 14C-labelled inulin ([14C]IN; n 5). Repeated 24 h collections of urine, corrected to 100% [3H]PAH or [14C]IN recovery, were used for accurate determination of N balances, 24 h urinary excretion of urea, creatinine, and total N, and calculation of mean 24 h renal clearance rates for endogenous creatinine and inulin. N balances were slightly below zero, but not significantly different between feeding and fasting periods, indicating that correction to 100% [3H]PAH recovery resulted in slight overestimation of the final balances. During fasting, withdrawal of the dietary water and protein loads resulted in a dramatic decline in 24 h urinary volume, and urea and creatinine excretion. Large individual variations in 24 h urinary creatinine excretion (with relative variation coefficients up to 30%) confirmed that this is an unreliable index of the completeness of urine collection. In this respect, recovery rates of [3H]PAH proved far more consistent. Renal clearance values obtained in fed mink were in fair agreement with published data from cats, dogs and ferrets (Mustela putorius furo). Inulin clearance was about 30% higher than endogenous creatinine clearance, although its decline in response to fasting was not significant. In a separate study (Expt B) another ten female mink were equipped with osmotic pumps containing [3H]PAH for determination of 24 h excretion rates of purine derivatives. During feeding, allantoin accounted for more than 97% of the excretion of purine derivatives in urine, uric acid making up less than 2.5%, xanthine and hypoxanthine less than 1%. In fasted animals, urinary excretion of each of these purine derivatives declined to less than 50% of the feeding value. In conclusion, an experimental technique is presented for efficient and accurate measurements of daily urinary excretion of nitrogenous constituents, which allows for correct determination of N balances in adult mink and, presumably, in other mammalian species.

Long-term effect of manidipine on renal function and structure in uninephrectomized spontaneously hypertensive rats

1. Long-term effects of manidipine hydrochloride (MAN), a calcium channel blocker, were examined in three groups of spontaneously hypertensive rats (SHR). Group 1 was given uninephrectomy (UNX) and MAN treatment, group 2 was given UNX and was not treated with MAN and group 3 was given neither UNX nor MAN treatment. 2. At week 15 after UNX, inulin clearance in group 1 rats decreased compared with rats in groups 2 and 3, but remained at the same level at week 40, when the level in group 2 rats declined below that in rats in groups 1 and 3. 3. Glomerular and tubulointerstitial lesions did not differ at week 15 after UNX among the three groups, whereas at week 40 both were advanced in the order of groups 2, 1 and 3. 4. Proteinuria did not differ between rats in groups 1 and 2 over the experimental period. 5. At week 15, the kidney weights of group 1 rats were greater than those of group 2 rats, indicating more prominent tubular hypertrophy in the former group. This was confirmed by morphometry of the proximal tubuli. In contrast, the glomerular volumes of rats in groups 1 and 2 were enlarged compared with that of rats in group 3, with no difference between the former two groups. 6. The findings suggest that MAN exerts renoprotective effects in SHR, both with regard to function and morphology. An effect on glomerular haemodynamics was considered to more likely be the mechanism underlying the renoprotective effect of MAN rather than that of a lowering of systemic blood pressure. 7. Augmented tubular hypertrophy after MAN treatment was an unexpected finding of the present study and the biological significance of this finding remains to be explored.

[Calcitonin, a proximal-tubular-acting diuretic: lithium clearance measurements in humans]

Lithium clearance was used to investigate the effect of calcitonin on renal sodium excretion. Two sequential renal function tests, calcitonin and placebo treated, were performed in 6 healthy students. Intravenous administration of 0.5 mg human calcitonin (hCT) (Cibacalcin, Ciba-Geigy, Basel, Switzerland) significantly raised fractional excretion of sodium (FENa), from 1.73% (0.97%) to 3.63% (0.89%) (p < 0.001), and lithium clearance (Cli), from 35.1 (5.4) to 53.9 (8.5) ml/ min x 1.73 m2 (p < 0.01). By using inulin and lithium clearance we calculated proximal (PFR), distal (DFR) and total excreted sodium (TAN). Our results clearly demonstrate that hCT has a proximal diuretic effect in humans and that a calcitonin induced proximal sodium loss is compensated by increased sodium reabsorption within 80 minutes after hCT application. Calcitonin increases the excretion of lithium and has a potential to be used in lithium intoxication.

A comparison of the uricosuric effects in rats of diltiazem and derivatives of dihydropyridine (nicardipine and nifedipine)

The effects of nicardipine and nifedipine on the urinary excretion of urate were examined in rats and compared with those of diltiazem. Test drugs were administered to urethane-anesthetized oxonate-loaded rats by continuous i.v. infusion. Diltiazem (10 micrograms/rat/min), nicardipine (0.3 microgram/rat/min) and nifedipine (1.0 microgram/rat/min) caused similar reductions of systemic blood pressure and increased total renal blood flow. Diltiazem did not increase urine volume significantly. However, this drug produced obvious uricosuria, with a significant increase in the ratio of urate clearance to inulin clearance (Cua/Cin), which resulted from an increase in Cua, but not from changes in the glomerular filtration rate (GFR). Nicardipine had clear diuretic and uricosuric effects, with similar increases in Cua and GFR and, thus, no change in Cua/Cin. On the other hand, nifedipine did not have any significant effect on the renal handling of urate. These results suggest that nicardipine produces uricosuria in rats via alterations in renal hemodynamics, while the uricosuric effect of diltiazem involves the tubules, as well as alterations in renal hemodynamics.

Cadmium induced nephrotoxicity in rats

Onset of hypertension and nephropathy after 1,2, and 4 weeks of exposure to cadmium chloride (1 mg/kg, ip) was studied in rats by measuring changes in blood pressure and renal function (urinary output, electrolytes, serum creatinine, inulin clearance and Na+K+ ATPase). Significant decrease in body weight and rise in blood pressure were observed as early as one week of exposure while microalbuminuria was detected in 50% of the animals after 2 weeks. Na+K+ ATPase, a renal tubular enzyme, was depressed after 1 week with maximum lowering occurring after 4 weeks. There were no detectable changes in fluid intake, urine output, electrolytes, inulin clearance and serum creatinine even after 4 weeks. It is concluded that hypertension and tubular lesion set in earlier than glomerulopathy as indicated by microalbuminuria and the latter could be the consequence of rise in blood pressure.

A new method of measuring renal function in conscious rats without the use of radioisotopes

The purpose of the current experiment was to develop fast and accurate assays for measuring glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). An enzymatic method was developed for the determination of inulin, and a colorimetric method was developed for determination of p-aminohippurate (PAH) in the plasma and urine of rats. These assays are easily automated and do not require the use of radioisotopes or corrosive chemicals. Glomerular filtration rate was measured by the clearance of inulin, and effective renal plasma flow was measured by the clearance of PAH. Blood pressure, heart rate, and renal function (urine volume, electrolytes, GFR, and ERPF) were measured in conscious rats for 1.5 h prior to drug treatment and for 3 h after treatment. Baseline renal function was compared to historical data. Acute changes in GFR and ERPF following administration of the vasoconstrictor peptide endothelin-1 (ET-1) were accurately measured with results similar to those obtained with older methodologies. These new methods offer many advantages over previously described methods by eliminating the use of radioisotopes and harsh chemicals. In addition, these methods can be used with an automated instrument with high accuracy and precision. Therefore, these new methods can be used to accurately determine GFR and ERPF and are sensitive enough to detect acute changes in GFR and ERPF in conscious animals.

Assessment of the accuracy of quantitative urine collection in mink (Mustela vison) using osmotic pumps for continuous release of p-amino-hippuric acid and inulin

A method is described to assess the accuracy of quantitative collection of urine in small experimental animals using implanted Alzet osmotic pumps for continuous release of specific urinary markers. The nominal pumping rate (10.00 +/- 0.15 microliters/h; mean +/- SEM) of 10 osmotic pumps was verified (9.96 +/- 0.12 microliters/h) in a 10-day in vitro assay in isotonic saline at 39.0 degrees C. Ten adult female mink (1100 +/- 34 g) had a 2-ml osmotic pump implanted intraperitoneally for 7 days while maintained in metabolic cages on a conventional mink diet. In 5 mink the pumps contained [3H]-labelled p-aminohippuric acid (PAH) only. The remaining 5 animals received a pump containing [3H]-PAH and [14C]-labelled inulin. The experiment was well tolerated by all animals. In fed animals, the amount of urine collected per day was not influenced by the osmotic pumps, whereas 24 h of fasting (water allowed) caused a dramatic fall in urinary volume. In 4 consecutive 24-h collections of urine (n = 10 animals) the recovery of [3H]-PAH was 70.8 +/- 3.6% (range: 52.0-87.2%), and urinary plus faecal water (= total) recovery of [3H]-PAH averaged 77.0 +/- 3.7% (range: 60.3%-94.3%). For [14C]-inulin (n = 5 animals) the urinary and total recoveries were 68.4 +/- 2.2% and 77.2 +/- 2.4%, respectively. In urine the 14C to 3H counts-ratio was almost identical to that of the infusion solution, indicating that metabolic decomposition of the markers was negligible. The results indicate that the daily recovery of suitable urinary markers, released by implanted osmotic pumps, provides a reproducible and valid measure of the accuracy achieved in quantitative collection of urine in mink and probably also in other animal species. Hence, this technique may be useful in future studies on animal nutrition and/or drug disposition.

Influence of the degree of renal dysfunction on the pharmacokinetic properties of the novel recombinant plasminogen activator reteplase in rats

Reteplase (drug code: BM 06.022) is an unglycosylated recombinant plasminogen activator variant derived from human tissue-type plasminogen activator. The main metabolic organs of reteplase are the kidneys, liver, and blood, whereas human tissue-type plasminogen activator is predominantly cleared by the liver. Recent studies showed that reteplase plasma concentrations were significantly increased in severe acute renal failure. The purpose of the present study was to evaluate whether the degree of renal failure influences the pharmacokinetic properties of reteplase. Subacute renal failure in rats was induced by bilateral 1-hr clamping of the renal arteries and recovery for 3 or 6 days. Acute renal failure was induced by bilateral surgical nephrectomy. Renal function was assessed by inulin clearance. The plasma concentration of functionally active reteplase was measured by an indirect spectrophotometric assay. Reteplase was administered as a double-bolus intravenous injection of 140 + 140 kU/kg, 30 min apart. In comparison with sham surgery, 1-hr clamping plus recovery for 6 days had the least effect on inulin clearance, followed by clamping and recovery for 3 days and bilateral nephrectomy (20.2 +/- 1.8 vs. 13.0 +/- 1.3, 8.3 +/- 0.8, and 3.1 +/- 0.2 ml center dot min-1 center dot kg-1, p < 0.01). Total plasma clearance of reteplase was significantly reduced, compared with sham surgery after 1-hr clamping plus 3-day recovery and bilateral nephrectomy (3.65 +/- 0.26 vs. 2.6 +/- 0.23 and 2.18 +/- 0.14 ml center dot min-1 center dot kg-1, p < 0.05 and p < 0.01, respectively), but not after 1-hr clamping plus 6-day recovery (3.33 +/- 0.34 ml center dot min-1 center dot kg-1, NS vs. sham surgery). There was a significant (p < 0.0001) linear correlation (r = 0.713) between the decrease of inulin clearance and the decrease of reteplase clearance. These data indicate that slight impairment of renal function does not significantly influence pharmacokinetic properties of reteplase, whereas severe renal dysfunction does.

Conventional measurement of renal function utilizing serum creatinine, creatinine clearance, inulin and para-aminohippuric acid clearance

Inulin and para-aminohippuric acid clearances, determined by the conventional method of continuous intravenous infusion with blood and urine sample collections, are the gold standards for estimating glomerular filtration rate and renal plasma flow, respectively. Creatinine clearance provides a reasonably good estimate of glomerular filtration rate but is still subject to errors in accuracy and precision. However, novel methods employing cimetidine to block renal tubular creatinine secretion hold promise for improving the accuracy of estimates. More importantly, a large (and growing) number of studies have consistently demonstrated that estimating glomerular filtration rate by creatinine clearance calculated from the Cockcroft-Gault formula is better than measuring creatinine clearance with a 24-h urine collection. Until newer, more simple methods are developed, calculating creatinine clearance using fasting serum creatinine level, body weight, age and sex provides a reasonable and clinically useful bedside measure of glomerular filtration rate for the practising clinician.

A new enzymatic method for the determination of inulin

A new enzymatic method for the determination of inulin in plasma and urine, using inulase (EC 3.2.1.7), fructokinase (EC 2.7.1.4), phosphoglucoisomerase (EC 5.3.1.9) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49) is described. The assay is based on the hydrolysis of inulin or Inutest (INutest which is the injectable form of inulin), by inulase and the determination of fructose released. The assay was linear up to 2 g/L of Inutest. The within-batch and between batch coefficients of variation were 2.3% and 2.2%, respectively. Recovery of added Inutest from plasma and urine was 98-102%. There was no interference from glucose (27.7 mmol/L), fructose (1.7 mmol/L) or mannose (1.7 mmol/L). When inulin clearance (using this method) and thiosulphate clearance were compared in 37 patients the inulin clearance was 9.3 mL/min (12%) lower than the thiosulphate clearance. We conclude that this enzymatic method is a simple and specific method.

Determination of inulin in plasma and urine by reversed-phase high-performance liquid chromatography

We report a new HPLC procedure for measuring inulin in plasma and urine. Samples after dilution are boiled in mild acidic conditions and then analyzed on a C18 column. Solvent system A is 3.2 mM HCl, pH 2.5, and B is acetonitrile-3.2 mM HCl (60:40, v/v), pH 2.5. The separation is carried out in 8 min with a flow-rate of 1.0 ml/min and the absorbance monitored at 280 nm. The relationship between inulin and the recorded peak area is linear from 0.2 to 3.2 mg/ml with a correlation coefficient of 0.999 for plasma and 0.999 for urine. Within-run precision, measured at three inulin concentrations, ranged from 0.9 to 1.7% in plasma and from 0.8 to 1.2% in urine. Between-run precision varied in plasma from 2.7 to 3.2% and in urine from 3.0 to 3.3%. Analytical recovery ranged from 102 to 107% in plasma and from 101 to 105% in urine, respectively. The method is sensitive, selective and only 30-microliters samples are required. Therefore, it could be used to evaluate the glomerular filtration rate even in small babies and to perform studies in animals.

Bosentan, an orally active endothelin antagonist: effect on the renal response to contrast media

PURPOSE

To examine the effect of bosentan, an orally active endothelin-receptor antagonist, on the renal response to contrast media in the isolated perfused rat kidney (IPRK) and to establish whether bosentan can inhibit contrast media-induced nephrotoxicity in a multiple-insult model in the conscious rat.

MATERIALS AND METHODS

Renal function was measured in the IPRK (n = 24) and in the rats that had undergone unilateral nephrectomy, were maintained on a salt-free diet, and were receiving indomethacin (10 mg/kg/d; n = 60).

RESULTS

In the IPRK, diatrizoate and iotrolan reduced the glomerular filtration rate and renal perfusate flow, an effect markedly inhibited by bosentan (n = 6 per group). In the multiple-insult rat model, the fall in creatinine clearance produced by diatrizoate was also markedly inhibited by bosentan (n = 15 per group).

CONCLUSION

Endothelin antagonists such as bosentan may be used to reduce the prevalence of contrast-induced nephrotoxicity.

Extracorporeal shock wave treatment raises blood pressure in borderline hypertensive rats

The long-term sequelae on kidney function and blood pressure of renal shock wave treatment were studied in normotensive Wistar rats, contralaterally nephrectomized Wistar rats and borderline hypertensive F1-hybrids bred from stroke-prone spontaneously hypertensive rats and Wistar-Kyoto rats. Renal shock wave treatment raised arterial blood pressure in borderline hypertensive, but not in normotensive, rats. A concomitant impairment of ipsilateral renal function or perfusion was not seen despite macroscopic and microscopic evidence of a loss of functioning parenchyma. We conclude that extracorporeal shock wave treatment, by way of its detrimental effects on the kidney, has the potential to provoke arterial hypertension in rats, provided that a genetic predisposition exists.

Toxicity and excretion of cisplatin in the avian kidney

Cisplatin is a widely applied antineoplastic drug with significant nephrotoxic potential. The purpose of this study was to define the toxic effect and excretion of cisplatin in the chicken, a species widely applied to the study of tubular transport mechanisms but little used for toxicology studies. Toxicity was assessed by the relative effect of cisplatin on renal clearances of the standard reference substrates inulin and p-aminohippurate (PAH) and by morphologic assessment of the kidneys of cisplatin-treated chickens. The data clearly support close similarities in the pattern of tubular cell damage produced in the chicken versus that reported for rats and human patients. It was further demonstrated that administration of an organic cation reduced Pt accumulation in the kidney and mitigated the toxicity as has been reported for rats. Excretion studies were carried out during unilateral renal portal infusion of cisplatin, and the results indicated that cisplatin does not undergo net tubular secretion as occurs in the rat and human. It can be concluded that, while the pattern of cisplatin-induced nephrotoxicity closely parallels that seen in mammals, the avian kidney exhibits a different pattern of urinary Pt excretion than does the mammalian kidney after cisplatin administration.

Drawbacks of the constant-infusion technique for measurement of renal function

We investigated the validity of the steady-state constant infusion method (CIM), in which quantitative urinary recovery and constant plasma concentrations of the solute infused are required. Successive 3-h clearances of inulin and p-aminohippuric acid (PAH) were determined for 27 h in 25 patients with renal disease. Results were compared with the standard method of bladder clearance (StM) and with a modified CIM (ModCIM). The 24-h urinary recovery was incomplete for both inulin and PAH. Mean 24-h ModCIM inulin clearance overestimated StM by 4.5 ml.min-1 x 1.73 m-2 (range 0-9, P < 0.001) independent of the extent of renal impairment and pointed to slow distribution and/or extrarenal clearance of inulin. For PAH, the difference between ModCIM and StM clearance was related to the average PAH clearance by ModCIM and StM (r = 0.78). Furthermore, neither plasma inulin nor PAH became completely constant, because of the circadian rhythm in renal function. In conclusion, the conditions of the steady-state CIM technique are not fulfilled, and the method is not suitable for accurate measurement of inulin and PAH clearance, especially when the clearance is low.

Short-term and sustained renal effects of angiotensin II receptor blockade in healthy subjects

We investigated the short-term and sustained hormonal and renal effects of angiotensin II (Ang II) receptor blockade in normotensive healthy volunteers. Twenty-four subjects maintained on a fixed sodium diet were randomized to receive for 8 days a placebo or 10 or 50 mg doses of the Ang II antagonist irbesartan (SR 47436, BMS 186295) according to a double-blind, parallel group design. Plasma renin activity, plasma immunoreactive Ang II and aldosterone levels, blood pressure, renal hemodynamics, and urinary electrolyte excretion were measured for 8 hours after the first and eighth administration of each dose of irbesartan or placebo. Ang II receptor blockade with irbesartan induced a dose-dependent compensatory increase in plasma renin activity and plasma angiotensin levels and a significant decrease in plasma aldosterone levels. The compensatory rise in plasma renin activity and Ang II levels was more pronounced on day 8, reflecting a long duration of the blocking effect of irbesartan. Irbesartan induced small changes in blood pressure and did not significantly modify renal blood flow and glomerular filtration rate. However, a significant decrease in filtration fraction was observed during receptor blockade on days 1 and 8. The tubular effects of irbesartan were characterized by a dose-dependent increase in sodium and chloride excretions. Interestingly, the cumulative natriuretic response to Ang II receptor blockade was similar on days 1 and 8, suggesting that in these subjects, renal Ang II receptors are not blocked over 24 hours during repeated administration even though this antagonist has a long duration of action (t1/2 of 15 to 17 hours).(ABSTRACT TRUNCATED AT 250 WORDS)

Amelioration of cisplatin nephrotoxicity with glycine: dose dependency in rats

The effects of glycine (0.1-1.0 g kg-1, i.v.) on the acute changes in renal haemodynamics and nephrotoxicity produced by cisplatin (6.0 mg kg-1, i.v.) were investigated in the rat. Cisplatin produced decreases of 50% in the clearance of [3H] inulin (CIN) and renal blood flow (RBF), 110 min following its injection. Glycine at a dose of 0.1 g kg-1 produced no attenuation of the cisplatin-induced decrease in CIN or RBF. Furthermore, this dose of glycine provided no significant protection of renal function over a 7-day period following cisplatin injection. By contrast, glycine at a dose of either 0.5 or 1.0 g kg-1 markedly attenuated cisplatin-induced falls in CIN and RBF, with the highest dose completely preventing any falls in these indices during the course of the experiment. Treatment with these higher doses of glycine produced prominent protection from the nephrotoxic actions of cisplatin, as evidenced by improvements in a range of indices of renal function which included plasma urea and creatinine concentrations, urine output, sodium excretion, CIN and the clearance of [14C] p-aminohippurate. The results of experiments with an intermediate dose of 0.25 g kg-1 glycine revealed some degree of amelioration of acute renal haemodynamic effects of cisplatin, particularly with regard to CIN; whilst in the nephrotoxicity study, 0.25 g kg-1 glycine produced a modest but significant reduction in cisplatin-induced acute renal dysfunction. The results have revealed a clear association between the acute renal haemodynamic effects produced by glycine in cisplatin-injected rats with the longer-term renal protective effects of glycine in cisplatin nephrotoxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Prevention of glomerular hypertrophy and glomerulosclerosis in Milan normotensive rats by low-protein diet, but not by low-dose captopril treatment

Milan normotensive rats, which spontaneously develop marked proteinuria (PU) and glomerulosclerosis (GS), were either kept on a normal-protein diet, a normal-protein diet with additional low-dose captopril (CAP), which did not affect blood pressure, or on a low-protein diet. After 8 months PU (79 +/- 25 mg/day) GS (3 +/- 2%) and total glomerular volume (TGV; 27.9 +/- 2.9 mm3/kidney) were significantly lower (p < 0.05) in the low-protein diet group than in both the normal-protein group (PU 583 +/- 210 mg/day, GS 12 +/- 5%, TGV 34.6 +/- 8 mm3/kidney) and the low-CAP group (PU 611 +/- 224 mg/day, GS 16 +/- 6%, TGV 41.8 +/- 8.6 mm3/kidney). In conclusion, the development of glomerular hypertrophy and GS in Milan normotensive rats was reduced by the low-protein diet, but not by low-CAP treatment.

Inulin measurement in serum and urine with an autoanalyser, corrected for glucose interference

A method is described for the semi-automated measurement of inulin concentrations in serum and urine in the presence of glucose. The concentration of glucose is measured simultaneously and is used to correct for almost all "inulin-like" interferences. The inulin standard curve is linear over a wide range (5-2500 mg/l). Between-run precision is < 6% and recovery from spiked sera is 98%. This method offers the possibility of measuring glomerular filtration rate in patients with varying glucose concentrations (e.g. diabetics).

Effects of gentamicin, neomycin and tobramycin on renal calcium and magnesium handling in two rat strains

1. Standard renal clearance techniques were used to compare the acute effects of gentamicin, neomycin and tobramycin on renal calcium and magnesium handling in Sprague-Dawley and Fischer 344 rats. 2. Significant hypercalciuric and hypermagnesiuric responses to all three drugs (P < 0.01) were apparent within 30 min of the onset of drug infusion. 3. The magnitude of the acute hypercalciuric and hypermagnesiuric response to the three aminoglycosides was comparable. This contrasts with their nephrotoxic action where neomycin >> gentamicin > tobramycin. The magnitude of the acute physiological responses to these drugs do not therefore reflect their nephrotoxic potential. 4. Sprague-Dawley rats were at least as responsive as Fischer rats in their acute renal responses to gentamicin. If Fischer rats are more sensitive to aminoglycoside nephrotoxicity than Sprague-Dawley rats, this is not reflected in their acute responses to gentamicin.

Improvement of therapeutic effect of human recombinant superoxide dismutase on ischemic acute renal failure in the rat via cationization and conjugation with polyethylene glycol

Therapeutic effect of superoxide dismutase (SOD) and three derivatives: a conjugate with polyethylene glycol (SOD-PEG2), a cationized derivative (cSOD), and a mannosylated derivative (Man-SOD), on acute renal failure induced by ischemia/reperfusion was studied in rats. SOD and derivatives were administered intravenously to the rat after nephrectomy of the right kidney and before and after 60 min occlusion of the left renal artery. At 48 hr after reperfusion, the renal function was evaluated by determining the urinary excretion rate of 14C-inulin injected intravenously. No therapeutic effect on the impaired renal function was shown in the case of low dose SOD (2600 unit/kg) treatment. In contrast, administration of cSOD which was shown to be taken up by the isolated perfused kidney from its capillary side and SOD-PEG2 which maintained high plasma concentration exhibited significant therapeutic effect, as did SOD at ten-fold higher dose (26,000 unit/kg). On the other hand, renal damage was promoted by Man-SOD. Thus, the present study demonstrated that chemical modification may improve the therapeutic effect of SOD on the ischemic acute renal failure and increased SOD concentration in the renal vascular space is an important factor for the improved effect.

Estimation of glomerular filtration rate and evaluation of renal function in ferrets (Mustela putorius furo)

Three methods of determining glomerular filtration rate (GFR) were performed in adult ferrets, 9 months to 7 years old. Endogenous creatinine clearance was determined, using serum and urine creatinine values obtained during 24- and 48-hour collection periods from 27 ferrets housed in metabolic cages. Creatinine and radiolabeled inulin were administered to 12 female ferrets by constant IV infusion during isoflurane-induced anesthesia. Serial 20-minute urine collections, together with serum samples obtained at the midpoint of urine collection, provided measures for clearance calculations of these substances. Mean +/- SD endogenous creatinine clearance in ferrets for metabolic cage collections was 2.50 +/- 0.93 ml/min/kg of body weight. There were no significant differences between the 24- and 48-hour clearance rates. Mean inulin clearance was 3.02 +/- 1.78, and mean exogenous creatinine clearance was 3.32 +/- 2.16 ml/min/kg. Analysis of variance, using least-squared means adjustment, did not yield any significant differences between inulin and exogenous creatinine clearance rates. Exogenous creatinine clearance-to-inulin clearance ratio was 0.99 +/- 0.46, and there was significant correlation between the 2 methods (r = 0.82, P = 0.0001). Significant body temperature effects on inulin or exogenous creatinine clearance were not found. Infused inulin clearance, the generally preferred method for GFR calculation in mammalian species, was significantly (P = 0.0069) higher in younger (3.65 ml/min/kg) vs older ferrets (2.29 ml/min/kg). Results of this study indicate that inulin clearance is an adequate measure of GFR in ferrets as it is in other species. Compared with inulin clearance, exogenous creatinine clearance also provides a reliable estimate of GFR in ferrets.

L-arginine administration normalizes pressure natriuresis in hypertensive Dahl rats

A blunted pressure-natriuretic response characterizes hypertension in the Dahl salt-sensitive rat. Long-term L-arginine administration prevents hypertension in these animals. To determine if long-term L-arginine corrects the pressure-natriuretic response, we gave salt-sensitive rats on an 8% sodium diet L-arginine or vehicle daily for 3 weeks. Identically treated salt-resistant rats served as controls. After 3 weeks, acute pressure-natriuresis curves were determined. To control for hypertension-induced renal damage, we also examined pressure natriuresis in salt-sensitive rats after short-term L-arginine. Baseline mean arterial pressure was 158 +/- 3 mm Hg in vehicle-treated salt-sensitive rats and 127 +/- 3 mm Hg in chronically L-arginine-treated salt-sensitive rats. During alterations in perfusion pressure, renal blood flow was autoregulated in all groups. Glomerular filtration rate was autoregulated in salt-resistant rats and L-arginine-treated salt-sensitive rats but fell with decreasing pressure in vehicle-treated salt-sensitive rats. Sodium excretion was greater (P < .05) in L-arginine-treated than in vehicle-treated salt-sensitive rats and did not differ from salt-resistant rats at 100, 125, and 158 mm Hg. The slope of the pressure-natriuresis relation was greater (P < .05) in chronically L-arginine-treated than in vehicle-treated salt-sensitive rats. L-Arginine had no effect on natriuresis in salt-resistant rats. Thus, long-term L-arginine administration normalizes pressure-natriuretic responses in salt-sensitive rats. The effect is not due to the prevention of renal damage and is specific to the salt-sensitive strain.(ABSTRACT TRUNCATED AT 250 WORDS)

Automated enzymatic analysis of inulin

We have developed an automated enzymatic assay for quantitation of inulin in plasma and urine that can be performed on the Cobas FARA II. In the assay, inulinase hydrolyzes inulin to fructose, and sorbitol dehydrogenase converts fructose to sorbitol with consumption of NADH, which is detected by spectrophotometry. The method incorporates a sample blank (inactivated inulinase) for each specimen to subtract contributions of endogenous fructose. Recovery of fructose or inulin was near 100%, with linearity to 300 mg/L. The enzymatic assay (y) agreed well with an anthrone comparison method (x) for analysis of inulin in both urine specimens (y = 1.00x - 138; Sy/x = 714) and plasma specimens (y = 1.00x - 3.5; Sy/x = 5.5). Glucose at 300 mg/L yielded an apparent inulin value of 1.3 mg/L in the enzymatic assay, but reacted at nearly 10% equivalency in the anthrone assay. Interferences from sorbitol, mannitol, and xylitol were negligible. CVs for day-to-day precision studies were 1-4%. The automated enzymatic assay of inulin is faster and avoids the use of caustic reagents required by the classical anthrone method.