Effects of Supplementation of Branched-Chain Amino Acids to Reduced-Protein Diet on Skeletal Muscle Protein Synthesis and Degradation in the Fed and Fasted States in a Piglet Model

Supplementation of branched-chain amino acids (BCAA) has been demonstrated to promote skeletal muscle mass gain, but the mechanisms underlying this observation are still unknown. Since the regulation of muscle mass depends on a dynamic equilibrium (fasted losses–fed gains) in protein turnover, the aim of this study was to investigate the effects of BCAA supplementation on muscle protein synthesis and degradation in fed/fasted states and the related mechanisms. Fourteen 26- (Experiment 1) and 28-day-old (Experiment 2) piglets were fed reduced-protein diets without or with supplemental BCAA. After a four-week acclimation period, skeletal muscle mass and components of anabolic and catabolic signaling in muscle samples after overnight fasting were determined in Experiment 1. Pigs in Experiment 2 were implanted with carotid arterial, jugular venous, femoral arterial and venous catheters, and fed once hourly along with the intravenous infusion of NaH¹³CO₃ for 2 h, followed by a 6-h infusion of [1-¹³C]leucine. Muscle leucine kinetics were measured using arteriovenous difference technique. The mass of most muscles was increased by BCAA supplementation. During feeding, BCAA supplementation increased leucine uptake, protein synthesis, protein degradation and net transamination. The greater increase in protein synthesis than in protein degradation resulted in elevated protein deposition. Protein synthesis was strongly and positively correlated with the intramuscular net production of α-ketoisocaproate (KIC) and protein degradation. Moreover, BCAA supplementation enhanced the fasted-state phosphorylation of protein translation initiation factors and inhibited the protein-degradation signaling of ubiquitin-proteasome and autophagy-lysosome systems. In conclusion, supplementation of BCAA to reduced-protein diet increases fed-state protein synthesis and inhibits fasted-state protein degradation, both of which could contribute to the elevation of skeletal muscle mass in piglets. The effect of BCAA supplementation on muscle protein synthesis is associated with the increase in protein degradation and KIC production in the fed state.

Significant association of poor glycemic control with increased resistance in efferent arterioles--study of inulin and para-aminohippuric acid clearance in humans

AIMS

To examine whether glomerular hemodynamic parameters in humans are associated with glycemic control indices, by simultaneously measuring clearance of inulin (Cin) and para-aminohippuric acid (CPHA).

METHODS

Thirty-one subjects (age 55.4±14.7 years; 15 men and 16 women; 21 diabetics and 10 non-diabetics) were enrolled. Cin and CPAH were measured simultaneously. Afferent arteriolar resistance (Ra), efferent arteriolar resistance (Re), glomerular hydrostatic pressure (Pglo) and glomerular filtration fraction (FF) were calculated according to Gomez' formula.

RESULTS

FF correlated significantly and positively with fasting plasma glucose (FPG), hemoglobin A1c (HbA1c) and glycated albumin (GA) (r=0.396, p=0.0303; r=0.587, p=0.0007; r=0.525, p=0.0070, respectively). Pglo correlated significantly and positively with FPG, HbA1c and GA (r=0.572, p=0.0008; r=0.535, p=0.0019; r=0.540, p=0.0053, respectively). Although there was no significant correlation between Ra and glycemic control indices, Re correlated significantly and positively with HbA1c and GA (r=0.499, p=0.0043; r=0.592, p=0.0018, respectively). FF, Pglo and Re were associated significantly with HbA1c and GA after adjustment for age.

CONCLUSIONS

These results demonstrate, in humans, that poor glycemic control is associated with increased Re, but not Ra. It is suggested that increased Re causes increased Pglo, leading to increased FF. Thus, hemodynamic abnormalities with poor glycemic control may be related to glomerular hypertension in humans.

Relationship between serum TSH levels and intrarenal hemodynamic parameters in euthyroid subjects

OBJECTIVE

Low thyroid function may be associated with a reduced glomerular filtration rate (GFR) calculated on the basis of creatinine metabolism. Thyroid hormone directly affects serum creatinine in muscle and low thyroid function might exert a similar direct effect in the kidney. The goal of the study was to evaluate this possibility by assessment of the inulin-based GFR and to examine the mechanism underlying the reduction of GFR.

PATIENTS AND METHODS

Renal and glomerular hemodynamics were assessed by simultaneous measurements of plasma clearance of para-aminohippurate (CPAH) and inulin (Cin) in 26 patients with serum creatinine <1.00 mg/dl and without thyroid disease. All subjects were normotensive with or without antihypertensive treatment and were kept in a sodium-replete state. Renal and glomerular hemodynamics were calculated using Gomez's formulae.

RESULTS

Serum TSH, including within the normal range (0.69-4.30 μIU/ml), was positively correlated with vascular resistance at the afferent arteriole (Ra) (r=0.609, P=0.0010), but not at the efferent arteriole (Re). Serum TSH was significantly and negatively correlated with renal plasma flow (RPF), renal blood flow (RBF), and GFR (r=-0.456, P=0.0192; r=-0.438, P=0.0252; r=-0.505, P=0.0086 respectively). In multiple regression analysis, serum TSH was significantly positively associated with Ra after adjustment for age and mean blood pressure.

CONCLUSIONS

These findings suggest that low thyroid function, even within the normal range, is associated with reduced RPF, RBF, and GFR, which might be caused by a preferential increase in Ra.

A novel approach for blood purification: mixed-matrix membranes combining diffusion and adsorption in one step

Hemodialysis is a commonly used blood purification technique in patients requiring kidney replacement therapy. Sorbents could increase uremic retention solute removal efficiency but, because of poor biocompatibility, their use is often limited to the treatment of patients with acute poisoning. This paper proposes a novel membrane concept for combining diffusion and adsorption of uremic retention solutes in one step: the so-called mixed-matrix membrane (MMM). In this concept, adsorptive particles are incorporated in a macro-porous membrane layer whereas an extra particle-free membrane layer is introduced on the blood-contacting side of the membrane to improve hemocompatibility and prevent particle release. These dual-layer mixed-matrix membranes have high clean-water permeance and high creatinine adsorption from creatinine model solutions. In human plasma, the removal of creatinine and of the protein-bound solute para-aminohippuric acid (PAH) by single and dual-layer membranes is in agreement with the removal achieved by the activated carbon particles alone, showing that under these experimental conditions the accessibility of the particles in the MMM is excellent. This study proves that the combination of diffusion and adsorption in a single step is possible and paves the way for the development of more efficient blood purification devices, excellently combining the advantages of both techniques.

Reducing shock number dramatically decreases lesion size in a juvenile kidney model

BACKGROUND AND PURPOSE

Adult stone patients are treated with several thousand lithotripter shockwaves (SWs) in order to pulverize a kidney stone. This typical clinical dose assures that the stone will be fractured completely. However, this same dose induces damage to the kidney, especially pediatric-size kidneys. If increasing SW number is known to increase renal injury and functional impairment, will reducing SW number below typical treatment levels significantly decrease kidney damage and hemodynamic changes?

MATERIALS AND METHODS

To address this question, one kidney in each of nine juvenile pigs (6-7 weeks old) was treated with 1000 SWs at 24 kV directed at a lower-pole calix with an unmodified HM-3 lithotripter. Parenchymal-lesion size was determined by sectioning the entire kidney and quantitating the amount of hemorrhage in each slice. Renal function was determined before and after SW treatment by inulin clearance, paraaminohippurate (PAH) extraction, and PAH clearance. The resulting morphologic and functional changes were then compared with those of kidneys that had been treated with a typical clinical dose of 2000 SWs (data previously published; J Am Soc Nephrol 2000;11:310). Eleven pigs were utilized as sham-treated controls.

RESULTS

Limiting SW number to 1000 significantly reduced the size of the lesion (by 95%) and reduced the degree of functional change (glomerular filtration rate by 38%, PAH extraction by 73%, renal plasma flow by 46%) compared with kidneys receiving 2000 SWs (an adult dose).

CONCLUSIONS

These data support the idea that SW number should be reduced to the lowest number that fractures kidney stones in order to minimize renal injury and functional impairment.

Renal elimination of p-aminohippurate (PAH) in response to three days of biliary obstruction in the rat. The role of OAT1 and OAT3

Pharmacokinetic studies of the drugs administered to subjects with mechanical cholestasis are scarce. The purpose of the present study was to examine the effects of bile duct ligation of 3 days (peak of elevation of serum bile acids and bilirubin) on the systemic and renal PAH clearance and on the expression of cortical renal OAT1 and OAT3 in a rat model. PAH is the prototypical substrate of the renal organic anion transport system. Male Wistar rats underwent a bile duct ligation (BDL rats). Pair-fed sham-operated rats served as controls. BDL rats displayed a significantly lower systemic PAH clearance. Renal studies revealed a reduction in the renal clearance and in the excreted and secreted load of PAH in BDL rats. The OAT1 protein expression in kidney homogenates was not modified, but it decreased in the basolateral membranes from BDL rats. In contrast, OAT3 abundance in both kidney cortex homogenates and in basolateral membranes increased by 3 days after the ligation. Immunocytochemical studies (light microscopic and confocal immunofluorescence microscopic analyses) confirmed the changes in the renal expression of these transport proteins. The present study demonstrates the key role of OAT1 expression in the impaired elimination of PAH after 3 days of obstructive cholestasis.

Simple HPLC–UV method for determination of iohexol, iothalamate, p-aminohippuric acid and n-acetyl-p-aminohippuric acid in human plasma and urine with ERPF, GFR and ERPF/GFR ratio determination using colorimetric analysis

A simple high-performance liquid chromatographic (HPLC) method was developed for the simultaneous determination of iohexol, iothalamate, p-aminohippuric acid (PAH) and n-acetyl-p-aminohippuric acid (n-acetyl-PAH) in human plasma and urine. A C(18) column at a flow rate of 1 ml/min with an aqueous mobile phase of trifluoroacetic acid (0.1% TFA in deionized water (pH 2.2), v/v) and methanol gradient was used for component separation. The plasma and urine assay demonstrated linearity from 10 to 50 microg/ml for iohexol and iothalamate, 5 to 40 microg/ml for PAH and 2.5 to 40 microg/ml for n-acetyl-PAH. The HPLC plasma and urine results obtained for PAH were used to calculate the subject kidney effective renal plasma flow (ERPF) and the iohexol results were used to calculate the subject kidney glomerular filtration rate (GFR). The HPLC results for PAH were then compared to an alternative colorimetric method for analyzing PAH to determine if subject metabolism (acetylation) of PAH affected the ERPF results obtained using the colorimetric method, the subsequent ERPF/GFR ratio and clinical impression of subject patient kidney function. The method was utilized in several different clinical studies evaluating the effect of kidney function from medications (phase IV evaluations) marketed for patients with cardiovascular disease.

Vagal cooling and concomitant portal norepinephrine infusion do not reduce net hepatic glucose uptake in conscious dogs

We examined the role of efferent neural signaling in regulation of net hepatic glucose uptake (NHGU) in two groups of conscious dogs with hollow perfusable coils around their vagus nerves, using tracer and arteriovenous difference techniques. Somatostatin, intraportal insulin and glucagon at fourfold basal and basal rates, and intraportal glucose at 3.8 mg.kg(-1).min(-1) were infused continuously. From 0 to 90 min [period 1 (P1)], the coils were perfused with a 37 degrees C solution. During period 2 [P2; 90-150 min in group 1 (n = 3); 90-180 min in group 2 (n = 6)], the coils were perfused with -15 degrees C solution to eliminate vagal signaling, and the coils were subsequently perfused with 37 degrees C solution during period 3 (P3). In addition, group 2 received an intraportal infusion of norepinephrine at 16 ng.kg(-1).min(-1) during P2. The effectiveness of vagal suppression was demonstrated by the increase in heart rate during P2 (111 +/- 17, 167 +/- 16, and 105 +/- 13 beats/min in group 1 and 71 +/- 6, 200 +/- 11, and 76 +/- 6 beats/min in group 2 during P1-P3, respectively) and by prolapse of the third eyelid during P2. Arterial plasma glucose, insulin, and glucagon concentrations; hepatic blood flow; and hepatic glucose load did not change significantly during P1-P3. NHGU during P1-P3 was 2.7 +/- 0.4, 4.1 +/- 0.6, and 4.0 +/- 1.2 mg.kg(-1).min(-1) in group 1 and 5.0 +/- 0.9, 5.6 +/- 0.7, and 6.1 +/- 0.9 mg.kg(-1).min(-1) in group 2 (not significant among periods). Interruption of vagal signaling with or without intraportal infusion of norepinephrine to augment sympathetic tone did not suppress NHGU during portal glucose delivery, suggesting the portal signal stimulates NHGU independently of vagal efferent flow.

A New HPLC Method to Determine Glomerular Filtration Rate and Effective Renal Plasma Flow in Conscious Dogs by Single Intravenous Administration of Iohexol and p-Aminohippuric Acid

A high-performance liquid chromatography method to determine iohexol (IOX) and p-aminohippuric acid (PAH) in the plasma of dogs is evaluated according to recovery, reproducibility, and linearity utilizing a gradient pump. The mobile phase consists of 50mM sodium dihydrogen phosphate with 0.5mM tetrabutylammonium chloride, the pH is adjusted to 4.1, methanol is added to the final ratio of 90:10 (v/v), the flow rate is set at 1 mL/min, and separation is achieved with an ODS2 Luna column. The UV detector is set at 254 nm. IOX and PAH are used for evaluation of the effective renal plasma flow (ERPF) and glomerular filtration rate (GFR). The present method tested in three dogs demonstrates the accuracy in the evaluation of ERPF and GFR. Because of its precision and simplicity and low cost, it can be considered a good tool for ERPF and GFR in small animal practice.

Rapid microplate method for PAH estimation

Evaluation of renal hemodynamics requires estimation of effective renal plasma flow, which is commonly measured by the renal clearance of p-aminohippuric acid (PAH). There are many existing methods for PAH assay that are complicated, expensive, or time consuming. We describe a rapid, precise, and accurate microplate-based assay of PAH using p-dimethylaminocinnamaldehyde, which produces a red color on reaction with PAH, and compare it with a reference HPLC method. Renal PAH clearances were measured in 10 volunteers, and clearances were calculated by using the new and HPLC methods. There was excellent agreement between the HPLC and the microplate method of PAH assay. The average ratio of microplate to HPLC method was nearly 1.0, and the limits of agreement (2 SD) for plasma, urine, and clearances were 17.2, 19.3, and 25.5%, respectively. Intraday coefficient of variation for urine and plasma was <7%; interday coefficient of variation was <6% for urine and plasma samples. The microplate method is a reliable alternative to a reference HPLC method and can be performed for a fraction of the cost, time, and reagents.

Acute and long-term effects of ACE inhibition on renal haemodynamics in glomerular and interstitial nephropathies

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors are the drugs of choice for the treatment of hypertension in patients with non-diabetic nephropathies. However, not every trial has reported better results with ACE inhibitors (ACE-I) than with other drugs. This study investigates whether the acute and chronic effects of ACE inhibition on renal and glomerular haemodynamics are similar in glomerular and interstitial nephropathies.

METHODS

We studied 20 hypertensive patients, on their usual diet, with mild-to-moderate chronic renal failure secondary to non-diabetic nephropathy. After a three-week wash out period, we determined plasma clearances of para-amino-hippurate and inulin before, and after acute oral administration of either enalapril or ramipril. This same test was carried out after one and two years of treatment with the same drug.

RESULTS

Acute ACE inhibition causes a decrease of renal perfusion, glomerular filtration and pressure with an increase of afferent resistances. Long-term ACE inhibition is associated only with a decrease in renal perfusion, with a non-significant tendency to higher filtration fraction and lower afferent resistances. All the renal haemodynamic modifications mentioned above are present only in patients with glomerular diseases.

CONCLUSIONS

Renal and glomerular haemodynamic responses are not similar after acute and chronic ACE inhibition. Only patients with glomerular diseases show acute or long-term responses to ACE inhibition.

Effects of gender on the pharmacokinetics of drugs secreted by the renal organic anions transport systems in the rat

The importance of considering sex differences in drug handling studies was admitted recently. The present work evaluates the sex influences on the pharmacokinetics of para-aminohippuric acid (PAH), the reference substance for the renal organic anion transports systems, and furosemide (FS), a standard loop diuretic which is also a substrate for this transport system. Female rats displayed a lower PAH and FS systemic clearance, and a lower value of the elimination rate microconstant from the central compartment for both drugs. These results may be explained by the diminution of the renal clearance of both PAH and FS observed in females. In summary, sex modifies the pharmacokinetics of organic anions. Although additional experimental work must be done to bridge the gap between studies using animals and humans, the reported experimental observations may have potentially important pharmacological implications. So, caution must be exercised in administering drugs like organic anions to females.

Effect of angiotensin-converting enzyme inhibitor on renal function in ovarian hyperstimulation syndrome in the rabbit

OBJECTIVE

To investigate renal function and whether captopril prevents alterations in the handling of sodium and water in the ovarian hyperstimulation syndrome (OHSS) in the rabbit.

DESIGN

Experimental study

SETTING

Physiology laboratory.

ANIMAL(S)

Six female New Zealand white rabbits were used as controls, and 13 were hyperstimulated with gonadotropins.

INTERVENTION(S)

Saline or captopril.

MAIN OUTCOME MEASURE(S)

Renal excretory and hemodynamic variables.

RESULT(S)

The 3% extracellular volume expansion in OHSS animals induced a significant elevation in mean arterial pressure by 27%, although increments in natriuresis and diuresis were similar to those observed in controls. The OHSS group had impaired pressure-natriuresis sensitivity compared with controls (0.36 +/- 0.07 microEq/min/g of Na excreted per mm Hg vs. 1.74 +/- 0.45 microEq/min/g of Na excreted per mm Hg; P<.05. Captopril significantly reduced mean arterial pressure (P<.05) and shifted the pressure-natriuresis response to the left by 0.85 +/- 0.17 microEq/min/g of Na excreted per mm Hg (P<.05).

CONCLUSION(S)

In OHSS in the rabbit model, pressure-natriuresis sensitivity is impaired. Angiotensin II may play a significant role in this phenomenon, since angiotensin-converting enzyme inhibition normalized the pressure-natriuresis relationship.

Impairment of renal vasodilation with l-arginine is related to more severe disease in untreated hypertensive patients

Data remain insufficient to place the decreased response to L-arginine in hypertensive patients within a consistent pathophysiological sequence. The aim of the present study in patients with essential hypertension was to assess the relationships between the response to L-arginine and a set of relevant clinical and laboratory parameters. In this prospective, interventional study, we administered L-arginine to untreated hypertensive individuals and healthy control subjects and measured the clearance of inulin and of para-aminohippurate and a set of biochemical and clinical variables. L-Arginine infusion revealed major differences between control subjects and 1 subgroup (group B) of hypertensive individuals. Group B hypertensives (n=18) had no increase in inulin clearance and no decrease in renal vascular resistance with L-arginine; however, in another subset of hypertensive patients (group A, n=27), the insulin clearance increased and renal vascular resistance decreased similar to the control group (group C, n=11). The ambulatory blood pressure monitoring in group B showed both an increased mean diastolic pressure and a "nondipper" pattern in the nocturnal regulation of arterial pressure. These findings in group B were accompanied by significant alterations in optic fundus and left ventricle hypertrophy and increased microalbuminuria (all, P<0.05). Furthermore, group B individuals had significantly lower values of HDL cholesterol and a higher baseline atherogenic index, plasma insulin level, and glucose/insulin index. We disclose a previously undescribed relationship between end organ repercussion and decreased renal hemodynamic response to L-arginine. Our results may help to understand the mechanisms that lead to target organ damage in hypertension.

Hypertension after neonatal uninephrectomy in rats precedes glomerular damage

The present study was designed to determine whether adult hypertension caused by a reduced number of nephrons from birth is due to preceding glomerular damage. Newborn male Sprague-Dawley rat pups were uninephrectomized during the first 24 hours after birth (UNX rats). At 20 weeks of age, chronically instrumented UNX animals were hypertensive on a normal-sodium (0.20%) diet compared with sham-operated controls (142+/-2 versus 124+/-2 mm Hg in controls). Body weights and the total kidney-to-body weight ratio were not significantly different in adult UNX animals compared with controls. Glomerular filtration rate (GFR) was reduced by 49% in UNX rats (1.85+/-0.24 versus 3.65+/-0.22 mL/min). Urine protein excretions were higher in UNX rats (20+/-2 versus 7+/-1 mg/d in controls). On a high-sodium (3.15%) diet, arterial pressure increased more in UNX than in controls (28+/-9 versus 3+/-1 mm Hg). In contrast, in animals studied at 8 weeks of age, GFR was only reduced by 26% in UNX animals (2.02+/-0.06 versus 2.73+/-0.07 mL/min). Their hypertension (125+/-2 versus 117+/-2 mm Hg) was also salt sensitive (increase on high-sodium diet of 35+/-11 versus 8+/-2 mm Hg in controls) but was not associated with proteinuria or histological signs of glomerular disease. Number of glomeruli per kidney in UNX animals was not different from controls, but individual glomerular volume increased by 41%. Thus, surgical removal of 50% of the nephrons, when done during development, causes reduced renal function and salt-sensitive hypertension in adulthood. Hypertension is present earlier in life than signs of glomerular disease, which suggests that hypertension is a major contributor to rather than primarily resulting from onset of renal disease.

Characterization of the mechanisms involved in the gender differences in p-aminohippurate renal elimination in rats

Gender differences in the renal handling on drugs and toxins have received too little attention. In the present study, a variety of preparations were used to examine the basis for the greater effectiveness of the male kidneys in the elimination of p-aminohippurate (PAH) in rats. Renal clearance of PAH was significantly lower in female rats as consequence of its smaller filtered and secreted load. The gender difference in the filtered load may be accounted for the lower value of glomerular filtration rate (GFR) displayed by female rats as compared with males. The lower value of the renal blood flow observed in females might explain, at least in part, the decrease in the GFR and in the secreted load of PAH. In females, maximal uptake for PAH transport into renal basolateral membrane vesicles decreased to 52+/-9% (P < 0.05) and Michaelis-Menten constant for PAH uptake into renal brush border membrane vesicles was increased to 163+/-8% (P < 0.05). These changes might also explain the lower secreted load of PAH. The sex difference in the renal clearance of PAH was also evidenced by the reduced systemic clearance observed in female rats.

The hippurate ratio as an indicator of functional hepatic reserve for resection of hepatocellular carcinoma in cirrhotic patients

Predicting the ability of the cirrhotic liver to withstand resection remains a challenge for the surgeon. This study evaluates the use of the hippurate ratio, a novel assessment of glycine conjugation of para-aminobenzoic acid by the liver, as a preoperative indicator of functional hepatic reserve. Between 1998 and 2000, sixty-one cirrhotic patients were prospectively assessed for hepatic resection using the hippurate ratio, indocyanine green retention at 15 minutes (ICG R-15), and other standard measures of liver function. Twenty-six patients were excluded as candidates for resection on the basis of inadequate functional hepatic reserve. Patients excluded from resection had significantly higher ICG R-15 values (29% +/- 9% vs. 16% +/- 12%, P = 0.001), higher Child-Pugh scores (5.9 +/- 0.9 vs. 5.3 +/- 0.4, P = 0.01), and lower hippurate ratios (30% +/- 14% vs. 45% +/- 15%, P = 0.005). There was a significant correlation between the hippurate ratio and ICG R-15. Other indicators of liver function such as factor V, factor VII, albumin, bilirubin, prothrombin time, and transaminases were no different between patients who did and those who did not undergo resection. Of the 35 patients resected, there were seven (20%) who developed varying degrees of liver failure with three perioperative deaths (8.5%). Patients who had some degree of liver failure had significantly lower hippurate ratios than patients who had no liver failure (29% +/- 10% vs. 48% +/- 14%, P = 0.002). There was no difference in ICG R-15 values between patients who had liver failure and those who did not. The hippurate ratio offers information on hepatocellular reserve that is not provided by other measures of liver function and may allow better selection of cirrhotic patients for liver resection.

Simultaneous determination of inulin and p-aminohippuric acid in plasma and urine by reversed-phase high-performance liquid chromatography

A simple, accurate and sensitive high-performance liquid chromatographic method with UV detection was carried out to measure simultaneously plasma and urine concentrations of both p-aminohippuric acid and inulin. Following a simplified acid hydrolysis of the sample, the separation was carried out in 4 min using a C18 reversed-phase column with a flow-rate of 1 ml/min, and monitoring the absorbance at 280 nm. Within the investigated concentration ranges of inulin (0.1-3.2 mg/ml) and p-aminohippuric acid (0.0097-0.3 mg/ml), good linearity (r>0.99) was obtained. Within-run RSD ranged from 2.9 to 6.1% and between-run RSD ranged from 6.4 to 10%. Analytical recoveries were 101-112%, with little differences between plasma and urine samples. The detection limit was 1 microg/ml for all the analytes studied. This method might be ideal for renal function studies where a rapid and reproducible assessment of both renal glomerular filtration rate and blood flow-rate is required.

Determination of efficacy of linotroban by inducing a reduction of renal inulin/para-aminohippuric acid clearances with the thromboxane A2 mimetic U-46619 in the conscious female rat

Linotroban (CAS 141443-73-4), a potent and selective thromboxane (TXA2) receptor antagonist, is known as a novel antithrombotic agent. It is suggested that pharmacological inhibition of TXA2 synthesis or action merits continued evaluation in the treatment of a variety of renal diseases. The aim of this study was the determination of efficacy of this new TXA2 receptor antagonist by assessing its effect on the reduction in inulin and para-aminohippuric acid (PAH) clearances induced by the TX/prostaglandin endoperoxide mimetic U-46619 in the conscious female rats. The following doses (3, 10, 30 mg/kg/24 h) of linotroban mixed with 720 micrograms TX-mimetic U-46619/kg/24 h were administered via osmotic pumps at a delivery rate of 10 microliters/h, implanted s.c. during 72 h. Rats of the U-46619 group were administered 720 micrograms U-46619/kg/24 h alone as described above, controls received 3.5% NaHCO3, respectively. Inulin/PAH clearances were determined at the end of the 4-h clearance period (68 h-72 h). Summarizing the data, glomerular filtration rate (GFR) and PAH clearances were reduced significantly by U-46619. When linotroban (3, 10 or 30 mg/kg/24 h) was added to U-46619 the GFR and PAH clearance were reversed to values that showed no significant differences to the controls.

High-performance liquid chromatographic determination of p-aminohippuric acid and iothalamate in human serum and urine: comparison of two sample preparation methods

A high-performance liquid chromatography method applied to determine p-aminohippuric acid (PAH) and iothalamate (IOT) in serum and urine samples of patients was evaluated according to recovery, reproducibility and linearity utilizing narrow-bore columns. The mobile phase consisted of 0.15 M sodium dihydrogenphosphate with 1.2 mM tetrabutylammonium sulphate, the pH was adjusted to pH 4.6, acetonitrile was added to a final ratio of 95:5 (v/v), the flow-rate was set at 0.3 ml/min. The separation was achieved on a ODS Hypersil column (200 x 2.1 mm I.D.). The UV detector was set at 254 nm. PAH and IOT are used for evaluation of kidney function [effective renal plasma flow (ERPF) and glomerular filtration rate (GFR)]). Under the described chromatographic conditions two sample preparation techniques, ultrafiltration and acetonitrile precipitation were compared. The results demonstrate the accuracy of both methods in evaluation of ERPF and GFR. Due to its cost-effectiveness we recommend the acetonitrile precipitation method in clinical routine.

PAH extraction and estimation of plasma flow in human postischemic acute renal failure

We determined the effect of postischemic injury to the human renal allograft on p-aminohippurate (PAH) extraction (E(PAH)) and renal blood flow. We evaluated renal function in 44 allograft recipients on two occasions: 1-3 h after reperfusion (day 0) and again on postoperative day 7. On day 0 subsets underwent intraoperative determination of renal blood flow (n = 35) by Doppler flow meter and E(PAH) (n = 25) by renal venous assay. Blood flow was also determined in another subset of 16 recipients on postoperative day 7 by phase contrast-cine-magnetic resonance imaging, and E(PAH) was computed from the simultaneous PAH clearance. Glomerular filtration rate (GFR) on day 7 was used to divide subjects into recovering (n = 23) and sustained (n = 21) acute renal failure (ARF) groups, respectively. Despite profound depression of GFR in the sustained ARF group, renal plasma flow was only slightly depressed, averaging 296 +/- 162 ml. min(-1). 1.73 m(-2) on day 0 and 202 +/- 72 ml. min(-1). 1.73 m(-2) on day 7, respectively. These values did not differ from corresponding values in the recovering ARF group: 252 +/- 133 and 280 +/- 109 ml. min(-1). 1.73 m(-2), respectively. E(PAH) was profoundly depressed on day 0, averaging 18 +/- 14 and 10 +/- 7% in recovering and sustained ARF groups, respectively, vs. 86 +/- 6% in normal controls (P < 0.001). Corresponding values on day 7 remained significantly depressed at 65 +/- 20 and 11 +/- 22%, respectively. We conclude that postischemic injury to the renal allograft results in profound impairment of E(PAH) that persists for at least 7 days, even after the onset of recovery. An ensuing reduction in urinary PAH clearance results in a gross underestimate of renal plasma flow, which is close to the normal range in the initiation, maintenance, and recovery stages of this injury.

Relationship between kidney size, renal injury, and renal impairment induced by shock wave lithotripsy

The relationship between kidney size and impaired renal function induced by shock-wave lithotripsy (SWL) was examined in 6- and 10-wk-old anesthetized pigs. Each pig received 2000 shock waves, 24 kV, or sham SWL to the lower pole calyx of one kidney. Bilateral GFR, renal plasma flow (RPF), and para-aminohippurate extraction was measured 1 h before and 1 and 4 h after SWL. The kidneys were then removed for morphometric analysis. Mean kidney weights were 66.1+/-2.7 g (n = 9) and 103.1+/-3.3 g (n = 8) in the SWL groups, and 60.1+/-2.6 g (n = 9) and 82.3+/-4.0 g (n = 9) in the sham-SWL groups. SWL-induced lesions occupied a significantly greater volume of the small kidneys (6.1+/-1.7 vol % versus 1.5+/-0.2 vol% in the large kidneys). RPF was significantly reduced by SWL in small and large kidneys, but to a significantly greater extent in small kidneys. RPF was also significantly reduced in the contralateral kidneys of both groups, but only at 1 h after SWL. SWL significantly reduced GFR to similar degrees in both kidneys of both groups, regardless of kidney size. Para-aminohippurate extraction was likewise reduced to similar degrees in both groups, but this effect was evident only in the SWL-treated kidneys, and only in the pole to which the shock waves had been applied. The injury induced by SWL affected a larger fraction of small kidneys than large ones, and the renal vasoconstriction induced by SWL was greatest in small kidneys.

Simultaneous determination of inulin and p-aminohippuric acid (PAH) in human plasma and urine by high-performance liquid chromatography

Inulin and p-aminohippuric acid (PAH) clearances are used for the estimation of glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). A simple and rapid high-performance liquid chromatography (HPLC) method with UV detection is described for the simultaneous determination of inulin and PAH in the same chromatogram in the plasma and urine of humans. Plasma and urine samples were hydrolyzed with perchloric acid (0.7%) in boiling water. The mobile phase consisted of 0.01 M potassium dihydrogenphosphate with 0.02 M tetramethylammonium chloride and o-phosphoric acid (pH 3)-acetonitrile (94:6, v/v), pumped at a rate of 1.2 ml min-1 on a C8 reversed-phase column. Tannic acid was used as the internal standard and UV detection at 285 nm was employed. The calibration curves were linear over the concentration range of 12.5-100 mg l-1 for inulin and 6.25-50 mg l-1 for PAH with determination coefficients greater than 0.997. The method is accurate (bias < 13%) and reproducible (intra- and inter-day relative standard deviation less than 11%), with a limit of quantitation of 12.5 mg l-1 and 6.25 mg l-1 for inulin and PAH, respectively. Analytical recoveries from urine and plasma were ranged from 81 to 108% for both compounds. This fully validated method, which allows the simultaneous determination of inulin and PAH clearances, is simple, rapid (total run time < 10 min) and requires only a 200 microliters plasma or urine sample.

Diclofenac does not decrease renal blood flow or glomerular filtration in elderly patients undergoing orthopedic surgery

Nonsteroidal antiinflammatory drugs (NSAIDs) have become increasingly popular in the treatment of perioperative pain. Due to concerns that cyclooxygenase inhibition may adversely affect renal function, these drugs are often not used in geriatric surgical patients. However, the perioperative effect of NSAIDs on renal blood flow (RBF) and glomerular filtration rate (GFR) has not been assessed. Therefore, using a prospective, controlled, double-blinded study design, we evaluated the effect of diclofenac on RBF and GFR in 20 patients (>65 yr) undergoing open reduction and internal fixation of the femur. All patients were normovolemic before the study. A standardized general anesthetic was administered. On induction of anesthesia, patients in the diclofenac group received an IV bolus of diclofenac (0.7 mg/kg) followed by a constant infusion (0.15 mg x kg(-1) x h(-1)) until the end of surgery. In the saline group, an equal volume of saline was administered. During four time periods (equilibration, anesthesia, surgical, recovery), GFR and effective renal plasma flow (ERPF) were measured by inulin and paraaminohippurate clearance, respectively. After the induction of anesthesia and throughout the surgical period, ERPF and GFR were significantly decreased compared with preoperative baseline values. However, no difference was demonstrated between the groups. These results suggest that, in geriatric surgical patients, the adjuvant administration of NSAIDs does not adversely affect renal function.

IMPLICATIONS

As determined by inulin and paraaminohippurate clearance, the intraoperative administration of diclofenac does not decrease glomerular filtration rate or effective renal plasma flow in normovolemic geriatric patients. Therefore, diclofenac may be administered during the perioperative period.

Renal arginine metabolism in fasted rats with subacute short bowel syndrome

1. Arginine can be produced in the kidney from citrulline. An important source of circulating citrulline is the intestinal breakdown of glutamine. Consequently, partial enterectomy leads to decreased plasma citrulline levels. The aim of the present study was to investigate the effect of diminished arterial citrulline levels on renal arginine production and total-body free arginine pools.2. Renal amino acid metabolism was studied 24 h after 75% small bowel resection in rats fasted overnight (16 h) (n=12; total fast 40 h). Sham-operated (n=9) and non-operated 16-h and 40-h fasted controls were studied in parallel (n=8/n=7). During anaesthesia, L-(2, 3-3H)-arginine and para-aminohippuric acid were infused until steady state. Subsequently, arterial and renal venous blood samples were taken. Concentrations of para-aminohippurate and amino acids and specific activity of arginine and citrulline were measured to calculate renal plasma flow, net renal uptake or release, and unidirectional influx or efflux of arginine and citrulline, as well as whole-body arginine turnover.3. Arterial citrulline was decreased in enterectomized rats compared with sham-operated rats (23+/-3 versus 44+/-6 microM). Net renal citrulline uptake and arginine release were almost stoichiometric (-36+/-7 and 38+/-6 nmol.min-1. 100 g-1 body weight respectively in sham-operated rats) and were both diminished by 50% in enterectomized versus sham-operated rats. In all groups, net renal arginine production accounted for less than 10% of whole-body rate of arginine appearance (488 nmol.min-1.100 g-1 body weight in the sham group). Despite decreased net renal citrulline consumption and renal arginine production in enterectomized rats, whole-body rate of arginine appearance and arterial arginine did not change significantly.4. In conclusion, net renal arginine production is reduced 24 h after 75% enterectomy in fasted rats. However, this does not have important effects on whole-body arginine production.

Simultaneous determination of p-aminohippuric acid, acetyl-p-aminohippuric acid and iothalamate in human plasma and urine by high-performance liquid chromatography

A sensitive and specific high-performance liquid chromatographic assay was developed for the simultaneous determination of p-aminohippuric acid (PAH), acetyl-p-aminohippuric acid (aPAH), and iothalamate in human plasma and urine. Plasma samples were prepared by protein precipitation with acetonitrile followed by evaporation, reconstitution in mobile phase, and injection onto a C18 reversed-phase column. Urine samples were diluted with 3 volumes of mobile phase prior to injection. Column effluent was monitored by UV detection at 254 nm. The lower limits of quantification in plasma were 0.5 mg/l for PAH and aPAH, and 1.0 mg/l for iothalamate. The within-day and between-day coefficients of variation in plasma and urine were < or =7.8% for all analytes. This method is well suited for renal function studies using iothalamate and PAH, whether administered as a bolus dose or by continuous infusion, to measure glomerular filtration rate and effective renal plasma flow, respectively.

Renal effects of the calcium channel blocker aranidipine and its active metabolite in anesthetized dogs and conscious spontaneously hypertensive rats

The purpose of this study was to investigate the renal effects of aranidipine, a novel calcium channel blocker of the dihydropyridine type, and its active metabolite in anesthetized dogs and conscious spontaneously hypertensive rats (SHRs). When infused into the renal artery in anesthetized dogs, aranidipine (0.03 microg/kg/min) induced sustained increases in urine volume and urinary excretion of sodium and of potassium. This effect was greater than that elicited by nifedipine (0.1 microg/kg/min). The aranidipine metabolite, M-1 (0.1 microg/kg/min), also caused diuresis and natriuresis almost equal to those of nifedipine. The stop-flow experiment using the anesthetized dog showed that intrarenal infusion of aranidipine (0.03 microg/kg/min), as well as nifedipine (0.1 microg/kg/min), produced natriuresis at the distal tubular site rather than at the proximal site. Aranidipine (0.3, 1, and 3 mg/kg), when administered orally, dose-dependently increased urine volume and urinary excretion of electrolytes in conscious saline-loaded SHRs. M-1 (10 mg/kg, p.o.) also showed diuretic and natriuretic effects comparable to those of nifedipine (10 mg/kg) in SHRs. In addition, after repeated oral administration of aranidipine for 7 days, short-term tolerance was not found for its diuretic and natriuretic effects in SHRs. These results suggest that, apart from antihypertensive efficiency, aranidipine may offer a therapeutic advantage by producing diuresis and natriuresis in hypertensive patients. The metabolite of aranidipine may contribute, in part, to the diuretic, natriuretic, and antihypertensive effects of aranidipine.

Chromatographic estimation of iothalamate and p-aminohippuric acid to measure glomerular filtration rate and effective renal plasma flow in humans

Iothalamate (IOT) clearance and p-aminohippuric acid (PAH) clearance are used for estimation of glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). A simple and rapid method is described for simultaneous determination of IOT and PAH in the same chromatogram in the serum and urine of humans. The mobile phase consisted of methanol-50 mM sodium monobasic phosphate with 0.5 mM tetrabutyl ammonium hydrogen sulfate (18:82, v/v), pumped at a rate of 0.8 ml/min on a C18 reversed-phase column. Samples of serum and urine were deproteinized with two volumes of acetonitrile containing the internal standard, p-aminobenzoic acid (PABA). The UV detector was set at 254 nm and peak height ratios of PAH or IOT to PABA were calculated with an integrator. Precision and accuracy were within 15% for both PAH and IOT. The recovery of PAH in urine and serum were 94% and 91%, respectively. For IOT the corresponding recoveries were 93% and 92%, respectively. This method clearly distinguishes acetyl-PAH from PAH and has been validated in healthy volunteers.

Rapid determination of p-aminohippuric acid in serum and urine by high-performance liquid chromatography

We report a simple and rapid HPLC procedure for measuring p-aminohippuric acid in serum and urine. After deproteinization with acetonitrile and addition of p-aminobenzoic acid as an internal standard, the chromatographic run is performed on a C18 column with the absorbance detector set at 275 nm. The separation is carried out in 10 min at a flow-rate of 1.0 ml/min with a mobile phase composed of 7 mmol/l 1-decanesulfonic acid, pH 3.70, and acetonitrile (82:18, v/v). The relationship between p-aminohippuric acid concentration and the p-aminohippuric acid/internal standard peak area is linear up to 100 microg/ml. Within-run precision measured at three different p-aminohippuric acid concentrations ranges from 1.73 to 1.98% in serum and from 0.72 to 1.32% in urine. Between-run precision varies from 1.80 to 4.06% in serum and from 1.05 to 2.66% in urine. Analytical recovery is between 98.26 and 99.44% in serum and from 99.57 to 100.45% in urine. The method is very simple, sensitive, and requires small volumes of sample for the assay (100 microl). Therefore, it could be a useful tool for the analysis of p-aminohippuric acid in the evaluation of renal plasma flow.

Evidence against an effect of endothelin-1 on blood coagulation, fibrinolysis, and endothelial cell integrity in healthy men

On the basis of an array of preclinical experimental results, it has been widely assumed that endothelin-1 (ET-1) may affect blood coagulation, fibrinolysis, and endothelial cell function, thereby playing a pathophysiological role in various cardiovascular diseases in humans. However, confirmation of this assumption is still lacking. ET-1 or placebo was administered intravenously to 12 healthy volunteers in a prospective, randomized, double-blind, crossover trial. Pathophysiologically relevant concentrations of ET-1 (an approximate threefold increase of normal blood levels) causing hemodynamic effects were reached by continuous intravenous infusion for 6 hours. Components of the coagulation (thrombin-antithrombin complexes, prothrombin fragment F1 + 2, activated factor VII, and factor VII antigen) and fibrinolytic (fibrin split product D-dimer, plasmin-plasmin inhibitor complex, tissue-type plasminogen activator, urokinase-type plasminogen activator, and plasminogen activator inhibitor-1) systems and markers of endothelial cell perturbation/dysfunction (von Willebrand factor and thrombomodulin) were measured before the start of infusion and after 2, 6, 12, and 24 hours. Comparing changes in the plasma concentrations of these parameters during and after infusion of ET-1 and placebo, we found no specific effects of ET-1. In contrast to previous reports from preclinical experiments, ET-1 does not appear to affect coagulation or fibrinolysis, nor does this peptide induce relevant endothelial cell perturbations in humans.

Laparoscopic cholecystectomy and time-course changes in renal function. The effect of the retraction method on renal function

BACKGROUND

Recently, the retraction method has been used to reduce intraabdominal pressure (IAP) during laparoscopic surgery. The purpose of this study was to determine the serial changes in renal function during laparoscopic cholecystectomy (LC) using the retraction method.

METHODS

Urine output, effective renal plasma flow (ERPF), and glomerular filtration rate (GFR) were measured serially in seven patients who underwent LC with 12 mmHg pneumoperitoneum (High-IAP group) and five who underwent LC using the retraction method with 4 mmHg pneumoperitoneum (Low-IAP group).

RESULTS

Urine output, ERPF, and GFR were decreased during pneumoperitoneum in the High-IAP group, whereas no significant changes in any of these parameters were observed in the Low-IAP group.

CONCLUSIONS

Our findings demonstrate that reduction of IAP to 4 mmHg using the retraction method prevents the transient renal dysfunction caused by prolonged 12 mmHg pneumoperitoneum during LC, suggesting that the retraction method reduces the risk of perioperative renal dysfunction during laparoscopic surgery.

[Renal hemodynamics and proteinuria in chronic glomerulonephritis treated with beta-receptor blockers or ace inhibitors]

BACKGROUND AND OBJECTIVE

In patients with chronic glomerular nephropathy associated arterial hypertension and proteinuria are considered to be cardinal risk factors in the progressive deterioration of renal function. Treatment regimens which reduce proteinuria and hypertension improve prognosis. The effect of the new beta-receptor blockers compared to common ACE-Inhibitors is of special interest.

PATIENTS AND METHODS

The studied cohort consisted of 11 patients with CGN, hypertension and proteinuria > 400 mg/24 h. Four drugs were given for 4 weeks, doubly blinded and randomized according to a "Latin-square design": Celiprolol (beta-1-antagonist, beta-2-agonist, 200 mg/d), Atenolol (selective beta-1-antagonist, 50 mg/d), Ramipril (ACE-inhibitor, 2.5 mg/d) and placebo. There was a two-week wash-out phase between each of the four treatment phases. At the end of each treatment phase glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were measured by inulin and para-amino-hippuric acid (PAH) clearance. Proteinuria was determined in the course of a three-day collection period at the end of each treatment phase. During this period blood pressures were measured with a continuous 24-hour blood pressure monitor.

RESULTS

Mean arterial blood pressure (MAP) was significantly reduced, compared with placebo, by all three antihypertensives (108 +/- 9 mm Hg with placebo, 98 +/- 12 mg Hg with atenolol, 101 +/- 11 mm Hg with celiprolol and 98 +/- 8 mm Hg with ramipril; P < 0.01). Celiprolol produced a significant rise In ERPF (322 +/- 109 ml/min with placebo, 391 +/- 110 ml/min with celiprolol: P < 0.05). GFR was slightly, but not significantly, reduced by celiprolol and atenolol. Filtration fraction remained unchanged with atenolol and celiprolol, while it was slightly, but not significantly, reduced with ramipril. Compared with the placebo, all three drugs significantly reduced proteinuria (P < 0.05): 1.8 +/- 1.3 g/24 h with placebo, 1.2 +/- 1.2 g/24 h with atenolol, 1.2 +/- 1.1 g/24 h with celiprolol and 1.4 +/- 1.4 g/24 h with ramipril.

CONCLUSION

These data indicate that, in addition to ACE inhibitors, the new generation of beta-receptor blockers in particular, because of their vasodilator action, favourably influence proteinuria and renal blood flow in patients with CGN and arterial hypertension.

Correlation between glomerular morphology and renal haemodynamic response to amino-acid administration in patients with IgA nephropathy

RATIONALE

To establish relationship, if any, between renal morphology and renal haemodynamic response to amino acids.

DESIGN AND METHODS

We investigated the correlation between renal haemodynamic regulation and morphology in a group of 15 patients with primary IgA nephropathy (IgAN) (age 26 +/- 2 years, BMI 24.4 +/- 1, GFR 64 +/- 5 ml/min, RPF 377 +/- 34 ml/min, FF 0.17 +/- 0.02). Twelve normal subjects (age 30 +/- 3 years, BMI 24 +/- 1, GFR 82 +/- 6 ml/min, RPF 421 +/- 42 ml/min, FF 0.19 +/- 0.02) were studied as controls. IgA patients were divided into two groups according to the histological staging of glomerular lesions: group I (n = 7) stage II, and group II (n = 8) stage III-IV.

RESULTS

In the basal state GFR was similar in the two groups and averaged 64 +/- 9 and 64 +/- 6 ml/min respectively. In contrast, FF was significantly lower in group II (0.14 +/- 0.01) (P < 0.05) in comparison to group I (0.21 +/- 0.03) and controls (0.19 +/- 0.02). In order to evaluate the renal functional reserve, all study groups underwent to an intravenous amino-acid infusion designed to increase plasma amino acid levels twofold (total from 2096 +/- 145 to 4301 +/- 221 mumol/l in IgA nephropathy patients and from 2272 +/- 83 to 3844 +/- 238 mumol/l in controls). In response to amino-acid infusion, GFR rose significantly in group I (GFR 20 +/- 2% and RPF 37 +/- 4% versus basal) and controls (GFR 20 +/- 2% and RPF 20 +/- 3% versus basal) (both P < 0.01 vs basal). In contrast, in patients with more severe glomerular lesions (group II) neither GFR nor RPF rose significantly (GFR -1 +/- 4% and RPF -8 +/- 6% versus basal) (P NS versus basal, P < 0.01 versus group I and controls).

CONCLUSIONS

The data show that in IgA nephropathy: severe forms of glomerular lesions are associated with a complex alteration of glomerular haemodynamic regulation, characterized by lower basal FF and loss of haemodynamic response to hyperaminoacidaemia.

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.

Effects of hypercholesterolemia of renal hemodynamics: study in patients with nephrotic syndrome

Experimental and clinical studies have demonstrated a positive relationship between hyperlipidemia and rate of progression of renal disease, suggesting that lipids can induce or aggravate glomerular injury mainly by interacting with mesangial cells. Nevertheless, recently has been demonstrated that increased cholesterol levels can also induce endothelial cell dysfunction. Thus, since endothelium is known to play a major role in modulating the vascular tone, we have tested the possibility that hypercholesterolemia impairs the renal hemodynamics in patients with active nephrotic syndrome and elevated serum cholesterol levels. In this single-blind, nonrandom study, 12 patients were treated with pravastatin (group T, treated, n = 12) and 8 with placebo (group C, controls, n = 8). The controls were studied after the pravastatin group had been completed. Before starting the treatment the patients underwent basal determinations including routine laboratory investigations and PAH and inulin clearances. The same determinations were repeated after 48 h, and 6 and 12 weeks from the beginning of the treatment. The study at 48 h was performed to see if pravastatin had a direct, cholesterol-independent effect on renal function. The following basal results were reported (mean +/- SEM; group T vs. group C): serum cholesterol (mmol/l) 9.7 +/- 0.4 vs. 9.1 +/- 0.3 (NS); proteinuria (g/24 h): 6.2 +/- 0.2 vs. 7.0 +/- 0.7 (NS); PAH clearance (ml/min): 353 +/- 21 vs. 385 +/- 31 (NS); inulin clearance (ml/min): 62.5 +/- 7.7 vs. 67 +/- 9.3 (NS). After 48 h, no changes were observed in both groups. Subsequently, in group T, the following percentage changes of basal levels were observed: serum cholesterol -21.4 +/- 3.2% at 6 weeks (p < 0.05) and -34.9 +/- 3.2% at 12 weeks (p < 0.01); inulin clearance +3 +/- 3.7% at 6 weeks (NS) and +9.3 +/- 2.9% at 12 weeks (p < 0.05); PAH clearance +7 +/- 3.1% at 6 weeks (p < 0.05) and +21.2 +/- 5.5% at 12 weeks (p < 0.01). By contrast, no significant changes of these parameters occurred in group C at any time, so that the percent changes of baseline values of CPAH were significantly greater in group T (at 6 weeks: p < 0.05; at 12 weeks p < 0.005). These results indicate that the reduction of cholesterol is associated with a significant increase in renal plasma flow, thus, suggesting that hypercholesterolemia may actually impair the renal hemodynamics. We speculate that this effect may contribute to increase the risk of ischemic acute renal failure in nephrotic patients and, along with changes induced in the mesangium by other mechanisms, to contribute to the progression of renal disease.

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.

Glycine conjugation of para-aminobenzoic acid (PABA): a quantitative test of liver function

OBJECTIVE

To evaluate glycine conjugation of para-aminobenzoic acid (PABA) to the hippurated metabolites, para-aminohippuric acid (PAHA), and para-acetamidohippuric acid (PAAHA) as a quantitative liver function test in patients with liver disease.

DESIGN AND METHODS

Serum concentrations of PABA and metabolites were measured by high pressure liquid chromatography in 24 controls and 50 patients with hepatobiliary disease.

RESULTS

Hippurate formation was significantly decreased in all patient groups with chronic liver disease versus controls. The hippurate ratio (% hippurated metabolites formed) correlated with severity of disease, serum albumin, and factor VII concentrations. PAHA concentration was a better prognostic indicator than factor VII concentrations in patients with acute liver disease; concentrations of zero correctly predicted a poor outcome in patients with fulminant liver failure.

CONCLUSIONS

Glycine conjugation of PABA may be useful as a quantitative liver function test in patients with hepatobiliary disease and as a prognostic index in patients with fulminant liver failure.

Comparison of 5-hydroxyindole-acetic acid and para-amino hippurate clearances in newborn rabbits

Recent study indicates that endogenous 5-hydroxyindole-acetic acid (5-HIAA) clearance can be used as an alternative procedure to para-amino hippurate (PAH) clearance for the estimation of renal plasma flow in human patients. In view of the limitations of PAH clearance measurements in newborn infants we made an attempt to validate the technique of measuring renal blood flow with 5-HIAA quantitatively against PAH clearance. Thirty-four simultaneous determinations of PAH and 5-HIAA clearances were performed in 14 newborn rabbits. 5-HIAA concentrations in plasma and urine were measured by using HPLC coupled with electrochemical detection (Beckman). Renal blood flow was found to range between 0.60 and 6.90 ml/min/kg (mean: 3.39 ml/min/kg) for 5-HIAA and from 0.93 to 6.61 ml/min/kg (mean: 3.68 ml/min/kg) for PAH clearances. There was a significant positive correlation between the values obtained by the two techniques (r = 0.84, P < 0.001). When 5-HIAA clearance was analyzed as a function of plasma 5-HIAA level only a weak, but statistically significant correlation could be detected (r = 0.33, P < 0.05). Plasma 5-HIAA measurement alone, therefore, does not reflect renal blood flow in newborn rabbits. It is concluded that endogenous 5-HIAA clearance might serve as a reliable estimate of renal blood flow in the neonate under different physiologic and pathologic conditions.

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.

Suppression of noradrenaline spillover by the dopamine prodrug gamma-L-glutamyl-L-dopa: a central effect?

The DA prodrug gamma-L-glutamyl-L-dopa (gludopa) has a high degree of renal selectivity with 2-step conversion to DA in the kidney. The effects of gludopa, with and without DA-2 receptor blockade, on renal and total noradrenaline (NA) spillover, were studied in two groups of rabbits. Eight rabbits received gludopa infusion (25 and 100 micrograms/kg/min and 8 received an infusion of gludopa and DA-2 receptor antagonist, YM-09151 (50 micrograms/kg i.v.). Renal and total NA spillover rates were measured by 3H-NA tracer method before and after gludopa infusion. Brain NA, DA, gludopa and L-dopa content were measured after gludopa infusion in 5 rabbits; control values for tissue catecholamine and drug levels were obtained in 5 untreated rabbits. Gludopa infusion markedly increased kidney DA content (300-fold) and DA excretion (6000-fold) but had little effect on plasma DA. It produced a dose-related fall in mean (+/- SEM) renal NA spillover (21.6 +/- 3.7 to 10.6 +/- 2.7, 7.2 +/- 2.7 ng/min, p < 0.01). Even greater falls were observed in total NA spillover after gludopa (43.1 +/- 10.2 to 19.7 +/- 3.4, 9.4 +/- 1.8 ng/min, p < 0.01). DA-2 receptor antagonism had no influence on the effects of gludopa on either renal or total NA spillover. Significant amounts of gludopa were detected in the brain after drug infusion (0.28 +/- 13 nmol/g brain tissue). Gludopa, a putative renal selective dopamine prodrug with effects mediated via DA-1 receptors also significantly inhibits both renal and extra-renal NA spillover. This effect is not a DA-2 effect but may be mediated centrally.

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.

Dipyrone and diclofenac do not influence creatinine-clearance, inulin-clearance or PAH-clearance in healthy male volunteers

The effects of the non-steroidal anti-inflammatory drug diclofenac and the pyrazolone derivative dipyrone on renal function were compared with those of placebo in 12 healthy male volunteers in a randomized, controlled, triple-crossover study with a wash-out period of 4 days between each of the 3 trial periods (dipyrone, diclofenac and placebo) which lasted three days each. The volunteers received dipyrone (1 g, 3 times/day for 2 days, followed by twice 1 g on the main trial day, which was day 3 of each study period) or diclofenac (50 mg, 3 times/day for 2 days, followed by twice 50 mg on the main trial day) or placebo orally. Standardized meals (50 mEq sodium per day) were given from one week before the start until the end of the study and on the main trial days a protein-rich lunch (2 g protein/kg body weight) was taken. Renal function was assessed in each study period by measurement of creatinine-clearance, inulin-clearance and p-aminohippurate (PAH)-clearance to characterize glomerular filtration rate and renal plasma flow. High protein intake induced glomerular hyperfiltration (increased creatinine-clearance, inulin-clearance and PAH-clearance) in all 3 study periods (dipyrone, diclofenac, placebo). Dipyrone and diclofenac had no effect on renal clearance of creatinine, inulin or PAH in comparison to placebo. These results show that dipyrone and diclofenac at therapeutic dosages over 3 days do not decrease glomerular filtration and renal plasma flow in healthy individuals. Furthermore, it is unlikely that prostaglandins play a major role in protein-induced glomerular hyperfiltration.

Nonmodulating trait may precede the development of hypertension

The nonmodulating trait thought to explain development of hypertension in 25 to 35% of patients, is characterized by abnormal angiotensin II (AII)-mediated control of aldosterone release and renal blood flow (RBF). Some data support the possibility that nonmodulation is an inherited trait, but others argue that it is an acquired epiphenomenon of the hypertensive state. We report the first case of a normotensive patient with nonmodulation who subsequently developed frank hypertension. Patient RR was studied on six occasions over a 5-year period, two while normotensive, four while hypertensive. This patient consistently demonstrated an abnormally low plasma aldosterone response to AII (3 ng/kg/min) on a low salt (10 mEq sodium) diet while both normotensive and hypertensive. A consistently abnormally depressed RBF response to AII on a high salt (150 to 200 mEq sodium) diet as well as a depressed RBF increment when the diet was changed from low salt to high salt were also noted. Thus, RR demonstrated nonmodulation by multiple criteria while both normotensive and hypertensive. We conclude that the nonmodulating trait may be a heritable defect that leads to the development of hypertension and is not an epiphenomenon.

A non-radioactive iothalamate and p-aminohippuric acid high-performance liquid chromatographic method for simultaneously measuring glomerular filtration rate and renal blood flow in the rat

A high-performance liquid chromatographic (HPLC) assay method has been developed for the quantitative determination of iothalamate and p-aminohippuric acid (PAH) concentrations in serum and urine samples in the male rat. Glomerular filtration rate (GFR) was measured as clearance of iothalamate, while effective renal blood flow (ERBF) was measured as clearance of PAH. The method is simple, rapid and sensitive and detects iothalamate and PAH in rat serum and urine following administration of bolus doses and continuous infusions of iothalamate and PAH. Samples of serum and urine were deproteinized with two volumes of acetonitrile containing the internal standard, and an aliquot chromatographed on a C18 reversed-phase column. The mobile phase was comprised of 0.1 M sodium phosphate with 1.2 mM tetrabutylammonium phosphate: methanol, 85:15 (v/v), at a flow rate of 1.0 mL/min. The analytical column eluate was monitored with a UV detector at 254 nm with quantitation achieved using peak-height ratios. The precision of the method was 6.6 and 3.6% for iothalamate in serum and urine, and 5.6 and 4.9% for PAH in serum and urine, respectively. The lower limit of quantitation was 0.63 microgram/mL for iothalamate and 1.25 microgram/mL for PAH in serum, and 3.1 microgram/mL for iothalamate and 1.5 microgram/mL for PAH in urine. Recovery of iothalamate from serum and urine was 99.9 and 93.5%, respectively. Recovery of PAH from serum and urine was 99.8 and 92.6%, respectively. The present study demonstrated that non-radioactive iothalamate and PAH can be measured simultaneously using a HPLC assay to measure GFR and ERBF in the male rat.

Renovascular resistance in primary hypertension: experimental variations detected by means of Doppler ultrasound

OBJECTIVE

To gauge the influence of renovascular resistance changes on blood flow velocity pulsatility in kidneys of hypertensive patients by means of the ultrasonic colour and pulsed-wave Doppler method, since we have previously shown in normotensive subjects that the blood flow velocity pulsatility in renal interlobar arteries varies with changes in renovascular resistance.

METHODS

In six male patients with primary hypertension, renal blood flow velocity profiles were investigated by means of duplex ultrasound. Single-kidney renovascular resistance was assessed by measurements of split renal function (gamma-camera renography), renal plasma flow (steady-state para-aminohippurate clearance) and cuff blood pressure. The pulsatility index of the blood flow velocity spectrum in the renal interlobar artery and renovascular resistance were measured either at rest, during infusion of angiotensin II, or after angiotensin converting enzyme inhibition.

RESULTS

A significant correlation existed between pulsatility index and renovascular resistance (r = 0.50, P < 0.002), which did not improve after correction for the blood pressure pulsatility. Changes of pulsatility index were more closely related (r = 0.64, P < 0.001) to the corresponding changes in renovascular resistance.

CONCLUSIONS

With the two-dimensional image-guided colour and pulsed-wave Doppler method it is possible to assess semiquantitatively small intra-individual changes in renovascular resistance in hypertensive patients by means of pulsatility index measurements. Pharmacologically induced alterations in renovascular haemodynamics may therefore be evaluated with this technique.

Increase in skeletal muscle blood flow but not in renal blood flow during euglycemic hyperinsulinemia in man

In order to investigate the effect of euglycemic hyperinsulinemia on skeletal muscle blood flow and renal blood flow, catheters were inserted into both femoral arteries, one femoral vein and one renal vein of 7 healthy men. Constant infusions of indocyanine-green dye (intraarterial) and of p-aminohippuric acid (intra-venous) were used to estimate leg plasma flow (ELPF) and renal blood flow (ERPF), respectively, prior to and during a euglycemic, hyperinsulinemic clamp (1.0 mU/kg.min of human insulin, serum concentrations of insulin before and during the clamp: 4.6 +/- 0.9 microU/ml and 65.5 +/- 20.6 microU/ml, respectively, t = 120 min). ERPF (basal: 1220 +/- 320 ml/min) remained unchanged throughout the period of induced hyperinsulinemia in each volunteer (mean: 1135 +/- 490 ml/min), whereas mean leg plasma flow (ELPF) rose from basal 206 +/- 99 ml/min up to 275 ml/min 90 minutes after the beginning of the euglycemic clamp study (p < 0.01). This was due to the marked rise in ELPF from 149 +/- 24 ml/min up to 243 +/- 25 ml/min (p < 0.01) seen in 5 subjects. In two men, who presented a markedly higher basal ELPF (332 and 365 ml/min, respectively), no further rise in ELPF was seen during induced hyperinsulinemia. Fractional renal extraction of insulin was unchanged during induced hyperinsulinemia (28 +/- 5%; basal: 22 +/- 18%), as was fractional extraction of insulin by the leg (10 +/- 5%; basal: 13 +/- 11%). The observed dissociation of ERPF and ELPF suggests a differential response to insulin in renal vs. leg vasculature which possibly is due to increased peripheral glucose metabolism.