GIT (Glucose Infusion Test): Polycentric Evaluation of a New Test for Vascular Access Recirculation

Introduction

Vascular access recirculation (AR), which is often unacknowledged, remains an important cause of inadequate dialytic dose. The glucose infusion test (GIT) is a new method for detecting and quantifying AR. This paper reports on a polycentric evaluation of the new test and a comparison with the classical Urea-test (UT).

Methods

GIT protocol comprises withdrawal from the arterial port (sample A), injection into the venous drip chamber of 1 g glucose in 4 seconds, withdrawal from the arterial port (sample B) continuously from 13 to 17 seconds. Glucose is determined on A and B by a reflectance photometer. If B = A then there is no recirculation. If B exceeds A by at least 20 mg/dl there is recirculation. AR quantification: AR% = (B-A) / 20. GIT was performed on 623 patients from eleven dialysis centers to screen the patients for AR. Subsequently, GIT and Urea-test (UT) were compared in 189 paired tests. The reproducibility of GIT and UT was studied in 28 paired tests performed in sequence.

Results

The screening test by GIT was positive in 68 cases (11 %). The majority of positivities was found in central venous catheters (CVC, 27/50 cases, 54 %), whereas only 7 % of artero-venous fistulas (AVF) were positive. In the CVC group, Tesio catheters were more frequently positive compared to Dual Lumen Catheters (64 % vs. 29 %). The comparison GIT – UT showed that results matched in 162 tests (79 negative and 83 positive both by GIT and UT), showing that on the grounds of UT, GIT has high sensitivity and specificity. In 27 tests GIT was positive, but UT negative. This disagreement is due to the different minimal limit of detection, 1 % for GIT and 5% for UT. The reproducibility was greater with GIT than with UT with a lower D % (respectively −0.6 ± 2.5 and −0.4 ± 6.1 %, p<0.001) and a lower coefficient of variation (17 vs 33 %).

Conclusions

The screening of 623 patients by GIT confirmed that AR in AVF is normally absent, whereas an unexpectedly high frequency of moderate AR in CVC was found. The GIT-UT comparison showed that the new test is simple and immediate, and gives results with higher accuracy, sensitivity and reproducibility than UT.

Correlation between pentosidine and endothelin-1 in subjects undergoing chronic hemodialysis

Advanced glycation end-products (AGEs), which accumulate in the blood and tissues of patients with chronic renal failure (CRF) undergoing chronic hemodialysis, play an important role in the pathogenesis of uremic complications. Endothelin 1 (ET1), a 21-amino acid peptide with vasoconstricting and mitogenic properties, is an important factor in the endothelial dysfunction occurring in uremia. The circulating levels of both AGEs and ET1 have been reported to be increased in chronic renal failure. In the present study we evaluated the possible relationship between pentosidine and ET1 plasma levels in CRF patients undergoing chronic hemodialysis treatment. The plasma concentrations of "free" and bound pentosidine (HPLC methods) and endothelin-1 (RIA method) were measured before the hemodialysis session in 40 nondiabetic CRF patients (22 males and 18 females; 54+/-3 years) on chronic hemodialysis for at least 1 year. Forty age- and sex-matched normal subjects served as a control group. In hemodialyzed patients, the overall pentosidine residues and pentosidine-free adduct plus pentosidine-free adduct bound reversibly to protein levels (24.9+/-2.04 pmol/mg protein and 110.5+/-5.9 pmol/ml, respectively) were significantly higher than those recorded in normal subjects (2.0+/-0.2 pmol/mg protein and 0.7+/-0.2 pmol/ml, respectively ). Endothelin-1 was also significantly (p<0.01) increased in CRF patients (10.6+/-0.4 pmol/ml in CRF patients and 2.7+/-0.3 pmol/ml in normal subjects). A significant positive correlation (p<0.01) was seen between "total" pentosidine (pentosidine residues and pentosidine-free adduct plus pentosidine-free adduct bound reversibly to protein) levels and endothelin-1 plasma values. The correlation between pentosidine and endothelin-1 provides further evidence that some AGEs exert a detrimental effect on the vascular endothelium, thereby contributing to the hypertension and other cardiovascular damage seen in CRF patients.

Online Convective Therapies: Results from a Hemofiltration Trial

With the introduction of the on-line preparation of dialysis fluids, the hemofiltration technique, which has never had a widespread diffusion in its old version with the infusion bags, has gained a new interest. We planned a prospective, randomized, 3-year-long study comparing survival and morbidity in ultrapure bicarbonate dialysis (BD) with on-line predilution hemofiltration (HF). Since comorbidity is one of the main factors limiting survival, the study was addressed to patients with a severe degree of comorbidity. The paper presents the preliminary results of the trial. Sixty-four patients were enrolled and randomized to either BD (N = 32) or HF (N = 32). Mean age and dialysis vintage were comparable. Twenty patients died during the study, 12 in BD and 8 in HF. The relative risk of death was 11% higher in patients treated with BD compared to those in the HF group (p < 0.005). The number of hospitalisation events per single patient was lower, even though not significantly, in HF compared to BD (1.94 + 1.26 in HF vs 2.48 + 1.98 in BD, p = NS). As concerns biochemistry, apart from beta-2-microglobulin, any other substantial difference was not found during the study, though the small solute concentration was generally a little more elevated in HF than in BD. Dialysis hypotension showed a trend to decrease in both the dialysis modalities up to near half of the trial, then, during the last year, it remained quite stable in HF, while, on the contrary, it increased in the BD group. By the end of the protocol, patients in HF showed a 2.5% incidence of acute dialysis hypotension, while patients in BD had 23%.

Phenylalanine hydroxylation across the kidney in humans rapid communication

Phenylalanine hydroxylation across the kidney in humans.

BACKGROUND

Although phenylalanine hydroxylase activity is detectable in in vitro renal tissue preparations, no data on in vivo phenylalanine hydroxylation across the human kidney, as well as on its possible contribution to whole-body hydroxylation, currently exist.

METHODS

To this aim, we have measured whole-body, renal, and splanchnic phenylalanine hydroxylation to tyrosine, as well as phenylalanine and tyrosine rates of appearance (Ra) and disposal (Rd), in postabsorptive subjects by means of renal and splanchnic arteriovenous catheterization combined with phenylalanine and tyrosine isotope infusions.

RESULTS

In the kidney, a relevant phenylalanine hydroxylation activity was detected (3.51 +/- 0.97 micromol/min x 1.73 m2 of body surface), whereas it was 2.48 +/- 1. 35 micromol/min x 1.73 m2 across the splanchnic area. These two sites together accounted for virtually the entire whole-body phenylalanine hydroxylation. Renal production of tyrosine from phenylalanine hydroxylation accounted for approximately 13% of whole-body tyrosine Ra, whereas renal total tyrosine Ra accounted for approximately 34% of whole-body tyrosine Ra. In the splanchnic area, these figures were approximately 9 and 40%, respectively. Hydroxylation accounted for approximately 70% of phenylalanine Rd in the kidney, as opposed to approximately 8% in the splanchnic area.

CONCLUSIONS

These data indicate that hydroxylation represents the major route of phenylalanine disposal within the kidney. The kidney and the splanchnic bed together account for all of the whole-body phenylalanine hydroxylation. These data also provide a further explanation for the reduced tyrosine pools occurring in uremia.

Diabetic nephropathy: from micro- to macroalbuminuria

This brief review will focus on the major factors leading to incipient diabetic nephropathy (i.e. microalbuminuria) progressing to overt nephropathy (i.e. macroalbuminuria) and particularly on the role of glycaemic control and hypertension. Both experimental and cohort studies support the role of hyperglycaemia in the development of diabetic nephropathy. Some recent long-term interventional studies in microalbuminuric patients show conflicting results regarding the role played by good metabolic control in reducing the incidence of overt nephropathy. However, strict metabolic control, which is fundamental in normoalbuminuric patients, is of little use even in microalbuminuric patients. In general, levels of glycosylated haemoglobin less than two standard deviations above the upper normal range, commonly <7.5-8%, seem to protect patients from developing nephropathy. The results of many cross-sectional studies have shown that the progression of renal damage regularly is accompanied by arterial hypertension both in insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM). Many long-term interventional studies have been performed in order to understand the effect of antihypertensive treatment on the incidence of proteinuria in both normotensive and hypertensive patients with IDDM or NIDDM. These data show a marked effect of antihypertensive therapy in preventing the onset of overt nephropathy, and suggest the superiority of angiotensin-converting enzyme (ACE) inhibitors. We believe that optimal blood pressure values are approximately 120/70-75 mmHg in younger patients and 125-130/80-85 mmHg in older patients. In conclusion, antihypertensive treatment, ACE inhibitors per se and possibly strict metabolic control reduce the development of nephropathy, thus playing a striking role in the secondary prevention of renal failure.

Somatostatin release in response to glucose is impaired in chronic renal failure

In order to evaluate somatostatin (SRIH) secretion in uremia, plasma SRIH concentrations were determined in basal conditions and after an oral glucose tolerance test (OGTT) in 14 non-dialysed patients with chronic renal failure (CRF), seven of whom had normal glucose tolerance (NGT) and seven impaired glucose tolerance (IGT). Plasma insulin, C-peptide and glucagon and blood glucose concentrations were also evaluated. The results were compared with those obtained in a group of age- and sex-matched normal subjects. In CRF patients, plasma SRIH fasting values (8.6 +/- 0.6 and 7.8 +/- 0.6 pmol/L in NGT and IGT patients, respectively) were comparable to those recorded in controls (7.7 +/- 0.5 pmol/L). SRIH response to OGTT, evaluated as area under curves (AUC) above basal, was similar in both groups of CRF patients (412.9 +/- 84.5 and 415.6 +/- 51.9 pmol/L per min), and significantly lower than in controls (660.1 +/- 58.5 pmol/L per min). Data indicate that chronic uremia induces a loss of SRIH secretory cell responsiveness to glucose. A possible effect of impaired SRIH secretion on glucose metabolism in CRF is discussed.

Inter-organ leptin exchange in humans

To assess the individual role of splanchnic organs, kidney, and peripheral tissues on leptin metabolism, leptin exchange across the splanchnic bed, kidney, and leg has been evaluated by the arterio-venous technique in post-absorptive non-obese subjects. Leptin levels in the hepatic and renal veins were significantly lower (p < 0.001), while femoral vein levels were consistently greater (p < 0.05) than in the artery. The fractional extraction of leptin, namely the percentage of arterial leptin extracted, was greater in splanchnic organs (16%) than in the kidney (9.5%). Urinary excretion of leptin was undetectable in most subjects, indicating that leptin is degraded within the kidney. There was no correlation between fractional extraction of leptin and glomerular filtration rate, whereas leptin fractional extraction was directly related to renal plasma flow (p = 0.017). Renal leptin clearance was about 50% of the glomerular filtration rate. Our data demonstrate that both splanchnic organs and the kidney cooperate in the disposal of leptin, while peripheral tissues add significant amounts of leptin to the circulation. In non-obese subjects the contribution of the kidney to whole body clearance is no more than 50%. The removal of leptin by the kidney depends on renal plasma flow but not on glomerular filtration rate or filtered leptin.

Intrarenal arteriosclerosis and impairment of kidney function in NIDDM subjects

It is currently under debate whether the pathogenesis of end-stage renal failure in non-insulin-dependent diabetes mellitus (NIDDM) is a consequence of microangiopathy alone. The aim of this study was to investigate intrarenal arteriosclerosis and its correlation with kidney function in NIDDM. In 36 diabetic subjects, and in 10 age- and sex-matched healthy control subjects we measured kidney volume and resistive index of the interlobar arteries by duplex Doppler ultrasonography. Clinical and metabolic parameters, renal function and vascular sequelae of the disease were also evaluated. In diabetic subjects resistive index (median 0.72, range 0.54-0.79) was higher than in control subjects (median 0.62, range 0.57-0.66) (2p < 0.002). Kidney volume and resistive index correlated with age (p < 0.004), body mass index (p < 0.001), mean blood pressure (p < 0.001), total and LDL cholesterol (p < 0.01) and creatinine clearance (p < 0.001 and < 0.01, respectively). Kidney volume also correlated with HbA1 (p < 0.01) and resistive index with uric acid (p < 0.01). Lower body macroangiopathy was associated with increased resistive index and reduced kidney volume (2p < 0.05), while upper body macroangiopathy and microangiopathy were not. Our data suggest that macroangiopathy rather than microangiopathy is mainly responsible for impairment of kidney function in NIDDM. The resistive index of interlobar arteries seems to be a reliable marker of intrarenal arteriosclerosis and can be used as a non-invasive, easily available parameter of its evolution.

Protein and amino acid metabolism in splanchnic organs in metabolic acidosis

Metabolic acidosis causes a cooperative participation of different organs such as the liver, kidney, and muscle in restoring acid-base balance. In splanchnic organs, metabolic acidosis has repercussions on several nitrogen metabolism pathways. The decrease in urea synthesis due to reduced activity of urea cycle enzymes, ammonia uptake and amino acid transport, and changes in glutamine metabolism support renal ammoniagenesis thus offering a response to rid the body of excess protons. While some of the mechanisms are adaptive others may be harmful for the body. Metabolic acidosis may have effects on splanchnic protein turnover. In severe acidosis, synthesis of secreted liver proteins may be reduced. Acidosis may also modulate the response of the liver to growth hormone (GH) for insulin-like growth factor-I synthesis, thus inducing a state of GH resistance. Splanchnic abnormalities in acidosis might contribute to the malnutrition observed in uremia.

Protein turnover in the kidney and the whole body in humans

For a better understanding of protein synthesis and degradation in the human kidney, the arteriovenous difference technique across the kidney, splanchnic organs, and leg muscle was combined with labeled leucine and phenylalanine isotope dilution models. Results indicate that in the postabsorptive state, the protein balance across the human kidney is negative because the rate of leucine release from protein degradation is greater than the amount used for protein synthesis. In the splanchnic bed, net protein balance is neutral since the amount of leucine deriving from protein degradation is similar to the amount utilized for protein synthesis. In the leg muscle, protein degradation exceeds protein synthesis. The kidney exhibits the highest leucine metabolic activity when expressed in terms of total organ leucine content. The estimated fractional protein synthesis rate in the human kidney is about 40% per day (vs. about 2% in muscle and 12% in the splanchnic bed). The human kidney presents high rates of protein turnover and accounts for a significant fraction of whole-body protein degradation, protein synthesis, and leucine oxidation.

Kidney, splanchnic, and leg protein turnover in humans. Insight from leucine and phenylalanine kinetics

The rate of kidney protein turnover in humans is not known. To this aim, we have measured kidney protein synthesis and degradation in postabsorptive humans using the arterio-venous catheterization technique combined with 14C-leucine, 15N-leucine, and 3H-phenylalanine tracer infusions. These measurements were compared with those obtained across the splanchnic bed, the legs (approximately muscle) and in the whole body. In the kidneys, protein balance was negative, as the rate of leucine release from protein degradation (16.8 +/- 5.1 mumol/min.1.73 m2) was greater (P < 0.02) than its uptake into protein synthesis (11.6 +/- 5.1 mumol/min. 1.73 m2). Splanchnic net protein balance was approximately 0 since leucine from protein degradation (32.1 +/- 9.9 mumol/min. 1.73 m2) and leucine into protein synthesis (30.8 +/- 11.5 mumol/min. 1.73 m2) were not different. In the legs, degradation exceeded synthesis (27.4 +/- 6.6 vs. 20.3 +/- 6.5 mumol/min. 1.73 m2, P < 0.02). The kidneys extracted alpha-ketoisocaproic acid, accounting for approximately 70% of net splanchnic alpha-ketoisocaproic acid release. The contributions by the kidneys to whole-body leucine rate of appearance, utilization for protein synthesis, and oxidation were approximately 11%, approximately 10%, and approximately 26%, respectively; those by the splanchnic area approximately 22%, approximately 27%, and approximately 18%; those from estimated total skeletal muscle approximately 37%, approximately 34%, and approximately 48%. Estimated fractional protein synthetic rates were approximately 42%/d in the kidneys, approximately 12% in the splanchnic area, and approximately 1.5% in muscle. This study reports the first estimates of kidney protein synthesis and degradation in humans, also in comparison with those measured in the splanchnic area, the legs, and the whole-body.

Renal metabolism of C-peptide in patients with early insulin-dependent diabetes mellitus

Renal metabolism of C-peptide was studied in 6 patients with early insulin-dependent diabetes mellitus (IDDM) with residual beta cell activity and in 11 nondiabetic subjects by the arterial-venous difference technique both in the postabsorptive state and for 80 min after ingestion of an amino acid mixture (0.8 g/kg). Urinary C-peptide (Cp) excretion, glomerular filtration rate and renal plasma flow were also measured. In the postabsorptive state in IDDM, renal uptake of Cp is reduced, while its urinary excretion and clearance are significantly increased. As a result, net renal extraction is markedly reduced. In contrast to controls, renal uptake and net extraction of C-peptide after amino acid ingestion do not increase in patients; the peritubular uptake evident in normal subjects is not detectable. Urinary excretion and clearance of Cp remain significantly higher in IDDM patients. In both groups, renal uptake of C-peptide is directly related to its renal load: however, in IDDM, the increase in Cp uptake for each increment in renal load is 35% lower than in controls (p < 0.001). Furthermore, as opposed to controls, urinary Cp excretion is not correlated with its arterial levels. Therefore IDDM patients have marked defects in renal handling of endogenous Cp, regarding both the amount metabolized by renal tissue and that reabsorbed by tubular cells. These data indicate an early alteration in the diabetic kidney that also impairs the reliability of urinary Cp evaluation as an index of residual beta cell activity in IDDM patients.

Plasma clearance rate of 51Cr-EDTA provides a precise and convenient technique for measurement of glomerular filtration rate in diabetic humans

It has not yet been fully clarified whether the plasma or renal clearance approach is the most reliable to investigate GFR in humans. The study presented here aimed to compare plasma decay with renal clearance of 51Cr-EDTA in 27 diabetic patients with patterns of renal function broadly dispersed in a wide range of values. Moreover, the comparison was also performed with renal clearance of nonlabeled iothalamate in a subgroup of 17 patients. A biexponential function was found to fulfill statistical and heuristic criteria for the modeling analysis of plasma 51Cr-EDTA decay with 19 samples after bolus intravenous 51Cr-EDTA injection. Individual GFR values from 51Cr-EDTA plasma clearance highly correlated with those from renal clearance (r2 = 0.977, P < 0.0001), but resulted on average about 2.5 mL.min-1.1.73 m-2 higher (66.8 +/- 6.5 mL.min-1.1.73 m-2 (mean +/- SE) versus 64.3 +/- 6.4, P < 0.02). This difference remained relatively constant from patients with normal renal function to those with impaired renal function, suggesting that the plasma clearance is slightly less accurate than renal clearance approach because of a constant extrarenal clearance rate. In the subgroup studied, a similar difference was found between GFR values from 51Cr-EDTA plasma clearance (84.7 +/- 7.3) and renal clearance of iothalamate (82.8 +/- 7.3), although not statistically significant (P = 0.4). Individual GFR values well correlated (r2 = 0.913, P < 0.0001). The precision and reproducibility of the experimental approaches were assessed by comparing three coefficients of variation: (1) CVb of the bolus injection, because of measurement errors; (2) CVc of the continuous infusion, which additionally includes errors of urine volume measurement and physiological variability in the same day; and (3) CVr of repeated measurements by using bolus injection, which also accounts for physiological variability in different days. CVc of iothalamate and 51Cr-EDTA infusions were 7.5 +/- 1.9% and 7.4 +/- 1.2% respectively. CVb and CVr of bolus injection of 51Cr-EDTA were 2.6 +/- 0.3% and 3.5 +/- 0.8% respectively. CVb and CVr of bolus injection of 51Cr-EDTA, but not CVc of iothalamate and 51Cr-EDTA infusions were twofold to tenfold lower than the percent yearly change reported in IDDM and NIDDM patients. More particularly, CVr was significantly less than CVc. In order to make the test less cumbersome, a reduced sampling schedule with seven samples was designed and validated. GFR measured with seven samples was 66.1 +/- 6.4 (P = 0.1 when compared with the full 19-sample schedule) with a CVb of 3.5 +/- 0.5%. This seven-sample protocol was not different from that obtained with the previously described simplified method of Brøchner-Mortensen (63.9 +/- 6.8, P = 0.16), yet yielding a statistically more accurate estimate (coefficient of variation for Brøchner-Mortensen method = 12.1 +/- 2.9, P = 0.004). Moreover, only bolus injection, along with modeling analysis of plasma clearance rate, allows the accurate measurement of the extracellular fluid volume, an important parameter in diabetic patients. It was concluded that the reduced seven-plasma sample protocol is able to detect as small as 4 to 5% changes per year in a single patient. Moreover, it provides precise and accurate estimate of GFR in diabetic patients with hyperfiltration, who are postulated to be at higher risk to develop renal damage.

Disposal of exogenous amino acids by muscle in patients with chronic renal failure

Muscle exchange of amino acids (AAs) was evaluated by using the arteriovenous-difference technique across the leg in seven patients with chronic renal failure (CRF) and eight control subjects before and for 75 min after the ingestion of an AA mixture simulating an animal-protein meal. Total AAs increased in arterial blood much more in patients with CRF after AA ingestion than in control subjects, as a consequence of an exaggerated increase in nonessential AAs (NEAAs) (+127%). Moreover, total AAs were taken up by the leg in larger amounts than in control subjects (+71%, P < 0.0025) because of increased uptake of NEAAs (+156%, P < 0.005). Branched-chain AA uptake by the leg was, in absolute values, similar to that of control subjects; however, because of the increased uptake of total AAs, branched-chain AA uptake was only 30% of total AA extraction, compared with 46% in control subjects. Abnormalities in AA uptake by muscle paralleled those in arterial AAs. In fact the same AAs that increased abnormally in blood were taken up by the leg at higher rates than in control subjects. Variations in arterial concentrations and muscle uptake of AAs were inversely related to arterial bicarbonate concentration, suggesting a role for acid-base status in modifying both the arterial supply and muscle metabolism of AAs. Results indicate that in CRF patients the normal pattern of postprandial AA repletion is disrupted. Muscle tissue faces the increased and unbalanced postprandial supply of AAs with an augmented and unbalanced uptake. Data are consistent with an abnormal use of exogenous AAs in CRF patients, possibly induced by metabolic acidosis.

Plasma beta-endorphin levels and glucose tolerance in patients with chronic renal failure

In order to examine the role of endogenous opioid peptides on glucose metabolism in uraemic patients, plasma concentrations of beta-endorphin, glucose, insulin and C-peptide were determined before and during an oral glucose tolerance test (OGTT) in nine non-dialysed patients with chronic renal failure (CRF). The results are compared with those obtained in a group of age-matched normal subjects. In CRF patients, plasma beta-endorphin fasting values (16.0 +/- 1.9 pmol/l) were significantly higher than those of the controls (6.6 +/- 0.6 pmol/l) and significantly correlated with the degree of renal function impairment. After glucose load, plasma beta-endorphin in CRF patients tended to decline, whereas in normal subjects increased. The fasting and the mean OGTT plasma beta-endorphin values negatively correlated with insulin initial response to glucose, insulin and C-peptide mean OGTT values, but not with glucose OGTT mean values. Data indicate that chronic uraemia induces a significant increase in circulating plasma beta-endorphin levels, with a loss of opioid system responsiveness to glucose. The possibility that this hyper-endorphinism may have a biological importance at least as a contributory factor of impaired glucose tolerance in uraemia may be suggested.

[Dopamine-induced variations in intrarenal resistance. Evaluation with Doppler ultrasound]

Low-dose dopamine is commonly used for the management of acute renal failure because of its exclusively renal vasodilator effect which is mediated through two specific receptors. However, the experimental background of this role is controversial in man. Indeed, the available data come mainly from animal trials and uncontrolled studies in patients with left ventricular dysfunction who need other drugs to improve cardiac output. This work was aimed at investigating Doppler value in assessing the effects of low-dose dopamine infusion in healthy subjects. Heart rate, arterial blood pressure and RI were measured before, during (at 10, 20 and 30 minutes) and after low-dose dopamine infusion in 4 healthy volunteers. In all subjects the RI reduced significantly, returning to the initial values after drug infusion. Indeed, the average RI (0.648 +/- 0.015 before drug administration) decreased to 0.595 +/- 0.026 within 10 min of infusion and remained almost the same during the infusion (0.596 +/- 0.024 within 20 min of infusion, 0.585 +/- 0.032 within 30 min). Within 10 min of the end of infusion, the average RI returned to similar values to those measured before drug administration (0.643 +/- 0.02). Changes in heart rate and arterial blood pressure were not significant. Our results confirm the vasodilator role of low-dose dopamine to be free of systemic effects in healthy volunteers with no therapeutic support which would cause extrarenal decrease in peripheral vascular resistance.

Skeletal muscle protein synthesis and degradation in patients with chronic renal failure

Muscle protein turnover and amino acid (AA) exchange across the forearm were studied in nine postabsorptive patients with chronic renal failure (CRF) under unrestricted calorie-protein diets and eight controls by using the arterio-venous difference technique associated with the 3H-phenylalanine kinetics. In patients with CRF: (1) the rate of appearance (Ra) of phenylalanine (Phe) from the forearm, reflecting proteolysis, was 27% increased in comparison with controls (P < 0.01). Also the rate of disposal (Rd) of Phe, reflecting protein synthesis, was increased in patients (P < 0.01). As a consequence of these counterbalanced alterations, net balance of Phe across the forearm, that is, net proteolysis, was not changed. (2) The release of total AA from the forearm was not different from controls. Valine and ketoisocaproate release was reduced (P < 0.05). Serine uptake was not detectable. (3) Net proteolysis and the Rd/Ra ratio were inversely and directly, respectively, related to arterial [HCO3-] (P < 0.02 and P < 0.03, respectively). (4) Moreover, net proteolysis and Phe Rd/Ra ratio were directly and inversely, respectively, correlated with plasma cortisol (P < 0.01 and < 0.005, respectively). Plasma cortisol was in the normal range and inversely related to arterial [HCO3-] (P < 0.02). (5) While in controls phenylalanine appearance from the forearm was inversely related to insulin levels, no correlation was found in patients. In conclusion, in patient with CRF, forearm Phe kinetics indicate the existence of an increased muscle protein turnover. Changes in protein synthesis and degradation are well balanced and net proteolysis is not augmented.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac diastolic abnormalities and atrial natriuretic factor in essential hypertension

Cardiac function and plasma levels of atrial natriuretic factor (ANF) were studied in a group of 38 patients with untreated essential hypertension and in a group of 31 well matched normotensive controls. ANF was slightly but significantly higher in hypertensives and was directly correlated with mean arterial pressure and inversely with plasma renin activity (PRA). Hypertensives showed normal systolic function and higher cardiac mass compared to controls. ANF was inversely correlated to echocardiographic indexes of left ventricular performance in the former group. At Doppler echocardiographic evaluation, hypertensives showed an impairment in diastolic function which was correlated to the increase in ANF levels. Stepwise multiple regression analysis performed with ANF as the dependent variable and several biohumoral and echocardiographic parameters as the independent variables showed that only cardiac diastolic function and PRA significantly affect ANF levels in hypertensives. In conclusion, an impairment in cardiac diastolic function may be responsible together with other factors for the increased ANF levels encountered in essential hypertension.

Erythropoietin treatment and amino acid metabolism in hemodialysis patients

A previous report suggests that treatment with recombinant human erythropoietin (rH-EPO) significantly improves many abnormalities in circulating amino acids (AA) in hemodialysis patients. We evaluated the effects of a 12-month treatment with rH-EPO (150-250 U/kg/week) on blood AA levels in 10 patients with chronic renal failure under regular dialytic treatment. During treatment, hemoglobin levels increased from 7.0 +/- 0.3 to 10.1 +/- 0.3 g/dl at 3 months remaining steady thereafter. Before the treatment, patients showed reduced levels of essential AA (EAA), mainly valine, leucine and threonine (p < 0.05-0.01); among non-EAA (NEAA), aspartate and serine were reduced, whereas glycine, alanine, proline, citrulline and cyst(e)ine were increased (p < 0.05-0.001). Val/Gly, Ser/Gly and Tyr/Phe ratios were low (p < 0.05-0.01). Total EAA and total NEAA (619 +/- 21 and 1,382 +/- 75 mumol/l, respectively, before the study) were unchanged (639 +/- 22 and 1,410 +/- 89 mumol/l, respectively) at 12 months. Abnormalities in AA levels observed before the treatment persisted throughout the study. Only serine increased at the end of the study (p < 0.05). In conclusion, contrary to what has been reported, treatment with rH-EPO is not associated with an amelioration of AA metabolism in hemodialysis patients.

Effects of a protein meal on blood amino acid profile in patients with chronic renal failure

Arterial whole blood levels of amino acids were determined in patients with chronic renal failure and in healthy subjects before and after 270 min after the ingestion of a grilled beefsteak (4 g/kg). In patients, total nonessential amino acids increased significantly more (+46%) than in controls owing to an exaggerated rise of serine, glutamine, proline, glycine, cyst(e)ine and alanine. Total essential amino acids increased as much as in controls; however, threonine, histidine and phenylalanine showed greater increases, while tryptophan had a smaller increment. Abnormalities in amino acid levels were even more evident in the postprandial period than in the postabsorptive state owing to reduced levels of valine, leucine, tryptophan, tyrosine, aspartate and glutamate and higher levels of glutamine, proline, glycine, cyst(e)ine, threonine, histidine and phenylalanine. Moreover, after the meal, the ratios total essential amino acids/total nonessential amino acids, valine/glycine, and branched-chain amino acids/total amino acids rose but persisted to be reduced whereas tryptophan/total amino acids and tyrosine/phenylalanine ratios increased in controls, but did not change in patients. In conclusion, in chronic renal failure, protein ingestion enhances the imbalance in amino acid levels already present in the postabsorptive state. The all data indicate that in patients with chronic renal failure, the metabolism of exogenous protein is impaired and the flow of amino acids to the organs is altered during the phase of body nitrogen replenishment.

Renal ammoniagenesis in humans with chronic potassium depletion

Renal ammonia production and distribution and ammonia precursor utilization were evaluated in eight patients with chronic potassium depletion (CPD) and aldosterone-producing adenoma and in 20 controls. In CPD, urinary ammonia excretion and ammonia added to renal venous blood were about twofold higher than in controls; thus, total ammonia production was significantly augmented (88.0 +/- 10.3 mumol/min.1.73 m2 vs. 45.0 +/- 2.6 in controls). Total ammonia production was inversely correlated with serum potassium and directly correlated with urine flow. Stepwise multiple regression analysis showed that both factors, mainly serum potassium, significantly influence ammonia production and account for 61.4% of variations in ammonia production. Renal extraction of glutamine was significantly increased (56.6 +/- 5.9 mumol/min.1.73 m2 vs. 34.6 +/- 3.1 in controls), and this could account for ammonia production. The ratio of urinary ammonia excretion to total ammonia production, an index of the intrarenal ammonia distribution, was similar in patients and controls, and was significantly correlated with urine pH and true renal blood flow (RBF). Stepwise multiple regression analysis showed that RBF, urine pH and urine flow also significantly affected ammonia distribution. However, these factors accounted for only 41.7% of variations in intrarenal ammonia partition, urine pH having a minor role. We conclude that in patients with CPD other factors besides urine pH, urine flow and RBF intervene in the ammonia partition between urine and blood.

Renal metabolism of amino acids in early insulin-dependent diabetes mellitus

Renal metabolism of amino acids (AAs) was evaluated in 5 patients with early IDDM, and in 7 controls (C) in the basal state for 80 minutes after the ingestion of an AA mixture simulating an animal protein meal. Insulin was withdrawn 20 hours before the study. Renal metabolism of AAs was evaluated by the arterial-venous difference technique. In the basal state in IDDM, as in C, the kidney takes up large amounts of a few nonessential AAs (NEAAs): it releases many NEAAs and a few essential AAs (EAAs). After AA ingestion in C, renal extraction of most EAAs, mainly BCAAs, Lys, and Thr, occurs; Pro extraction also increases and a significant uptake of Gly, Glu, Asp, Orn, and Tyr takes place. EAA extraction accounts for 30-40% of total AA uptake. In IDDM, after AA ingestion, a) renal uptake of total AAs is significantly lower, owing mainly to a markedly lower uptake of BCAAs, Lys, and also of Pro, Orn, and Ala; b) renal EAA uptake accounts for less than 20% of total AA extraction. These results indicate that in IDDM postprandial renal N repletion is impaired and unbalanced.

Long-term minoxidil treatment in refractory hypertension and renal failure

Twenty-two patients with severe or accelerated hypertension refractory to conventional hypotensive therapy have been treated with minoxidil for an extended period. Patients were divided in three groups according to different degrees of renal function or the presence of accelerated hypertension. In the first group (8 patients with normal or slightly decreased renal function) BP fell from 197 +/- 11/118 +/- 3 before minoxidil therapy to 157 +/- 7/98 +/- 2 after six months (p less than 0.001), and remained steady during the following eighteen months. In the second group (9 patients with creatinine clearance of 30 +/- 3 ml/min.1.73 m2) BP decreased from 192 +/- 9/119 +/- 4 to 147 +/- 6/91 +/- 4 at six months (p less than 0.001); renal function did not show any significant modification during the eighteen months of the study. In the third group (5 patients with accelerated hypertension) BP fell from 243 +/- 14/137 +/- 6 to 166 +/- 13/99 +/- 7 at six months (p less than 0.01). Seven patients, four in the first and three in the second group, were followed for more than six years; these patients, with mild renal insufficiency (creatinine clearance 50 +/- 4 ml/min) before minoxidil therapy, were on a protein unrestricted diet for the entire length of the study. In this group of patients BP fell from 182 +/- 9/115 +/- 3 to 150 +/- 6/96 +/- 2 after one year (p less than 0.01) and remained well controlled for the following six years or more. Renal function did not show any significant worsening over the years (monthly decrement in creatinine clearance 0.08 ml/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Splanchnic exchange of amino acids after amino acid ingestion in patients with chronic renal insufficiency

Splanchnic exchange (net uptake or release) of amino acids (AAs) was evaluated by measuring arterial-hepatic venous differences for AAs and hepatic blood flow in patients with chronic renal insufficiency (CRI) and control subjects before and for 70 min after the ingestion of an AA mixture simulating an animal protein meal. In CRI after AA ingestion, splanchnic exchange area for total nonessential AAs (NEAAs) is increased 135% over control subjects because of an augmented escape of proline, glutamate, serine, glycine, alanine, and cyst(e)ine; contrarily, glutamine shows an increased splanchnic uptake. Splanchnic exchange area for total essential AAs (EAAs) is increased only by 67% over controls because of a higher escape of threonine, isoleucine, phenylalanine, and histidine. Abnormalities in arterial areas for AAs parallel those in splanchnic areas except for glutamine and isoleucine. Data indicate that in CRI, at least for 70 min after an AA meal, splanchnic organs metabolize abnormally ingested AAs and export an increased and unbalanced bulk of AAs, severely affecting postprandial arterial profile of AAs.

Effect of amino acid ingestion on blood amino acid profile in patients with chronic renal failure

Arterial whole blood levels of amino acids (AA) were determined in patients with chronic renal failure (CRF) and in healthy volunteers before and for 75 min after the ingestion of an AA mixture simulating the AA content of an animal-protein meal. In CRF patients, total AA increased more than in control subjects as a consequence of an exaggerated rise in nonessential AA (+86%), mainly glutamine, proline, glutamate, serine, glycine, and alanine. Total essential AA in patients increased as much as in control subjects; however, threonine and phenylalanine showed greater increases while leucine had a smaller increase. As a consequence of the observed alterations, a striking unbalance in the postprandial pattern of arterial AA ensued in CRF patients. The flow of AA to all the organs is altered during the absorptive phase, which is crucial for body nitrogen-pool replenishment.

Renal metabolism of C-peptide in man

Renal metabolism of C-peptide was studied in nine nondiabetic nonobese patients with normal renal function by the arterial-venous difference technique before and after the oral administration of an amino acid mixture simulating an animal protein meal. In the basal state, the kidney removed 25.7 +/- 7.5% (+/- SD) of the arterial plasma C-peptide. Renal uptake was approximately 7-fold greater than urinary excretion, and thus, more than 85% of the amount extracted was metabolized by the kidney. Renal C-peptide clearance was very high and approximated the glomerular filtration rate, whereas urinary C-peptide clearance was only 14% of its renal clearance. Shortly after amino acid ingestion, arterial C-peptide levels increased by 107%, and C-peptide renal fractional extraction, uptake, and net metabolism also increased markedly (67%, 278%, and 328%, respectively); urinary clearance and excretion did not change. Renal clearance became 2-fold greater than the glomerular filtration rate, indicating that in this phase the kidney removed substantial amounts of C-peptide from peritubular blood as well as by filtration. Both renal uptake and urinary excretion of C-peptide were related to its arterial levels (P less than 0.001 and P less than 0.05, respectively), but renal uptake increased much more than urinary excretion for each increment in arterial C-peptide levels. These results indicate that renal C-peptide metabolism is considerable in the postabsorptive state and is even more marked during the postprandial period. The kidney, therefore, plays a key role in both the regulation of circulating plasma levels and the metabolic clearance of C-peptide.

Effects of hemodialysis on guanidinopropionic acid metabolism

Blood levels of guanidinopropionic acid (GPA), a putative uremic toxin, have been evaluated in 5 uremic patients before a dialytic session, at the end of it and during the following 68 h. GPA levels are markedly higher in uremic patients than in controls and are significantly reduced at the end of dialysis even if still higher than in controls. The clearance of GPA is similar to those of urea and creatinine, even if at the end of the dialysis session the percent decrease of GPA is significantly lower than that of urea. During the first 8 h after the end of dialysis GPA levels increase steeply; subsequently, the rate of accumulation of GPA in blood declines markedly remaining constant until the 68th hour. In conclusion GPA is markedly increased in blood of uremic patients and is significantly removed by dialysis. The evaluation of GPA increase per hour after the end of dialysis may provide an estimation of GPA production in uremic patients.

Leg metabolism of amino acids and ammonia in patients with chronic renal failure

Leg metabolism of amino acids and ammonia in the postabsorptive state was evaluated in 10 patients with chronic renal failure (CRF) and in 10 patients with normal renal function (controls) by measuring the arterial-femoral venous (A-FV) differences for free amino acids and ammonia. Total amino acid release from the leg and alanine and glutamine release, which accounts for the greatest amount of the total amino acid release, are similar in patients and controls. Total amino acid uptake from the arterial blood and glutamate uptake, which is the amino acid extracted at the highest rate, are comparable in both groups. Taken together these data, in addition to the similarity of A-FV differences for proteolytic markers, namely tyrosine, phenylalanine and histidine, suggest that protein breakdown in peripheral tissues is not increased in patients with CRF. In CRF selective metabolic abnormalities for some amino acids are evident. Whilst only the A-FV differences for valine, leucine and isoleucine are decreased, additional alterations are observed by relating the A-FV difference for each amino acid to that of proteolytic markers. Such a procedure demonstrates that in CRF histidine release relative to that of proteolytic markers is reduced, whereas proline and arginine release is increased. In CRF the reduced release of some amino acids, mainly branched-chain amino acids, by the leg probably affects the pattern of circulating amino acids. Finally, both in patients and in controls a significant uptake of ammonia is observed; the ammonia uptake is related to arterial levels of this metabolite, confirming the role of peripheral tissues in removing ammonia from circulation.

Branched-chain amino acid metabolism in chronic renal failure

Interorgan exchange of branched-chain amino acids (BCAA) in the postabsorptive state was evaluated in 16 patients with chronic renal failure (CRF) and in 20 subjects with normal renal function, by measuring arterial-venous differences of BCAAs across the leg, brain, hepato-splanchnic (HS) bed, and kidney. In CRF, arterial blood levels of valine are significantly reduced, whereas leucine and isoleucine levels are not different from controls; valine and leucine levels are directly related to GFR. In CRF, a significant decrease in the release of valine by the leg is observed; the leucine release tends to be lower; for both these amino acids, leg release is directly related to their arterial levels. Both ratios of valine and leucine release to total amino acid release by the leg are significantly reduced in CRF. Furthermore, in CRF cerebral uptake and fractional extraction of valine and isoleucine are decreased. In normal subjects, valine and leucine are significantly extracted by the HS bed, whereas in CRF the HS uptake of valine and its fractional extraction fall significantly and leucine uptake is unchanged. The kidney releases significant amounts of leucine both in CRF and in controls. In conclusion, in CRF in the postabsorptive state the exchange of BCAAs, mainly valine, is altered rather early at the major sites of production and utilization, and the flux of these amino acids among the organs is decreased. The primary defect is the decreased output by peripheral tissue, which reduces the supply of BCAAs to the brain and HS bed. Regional metabolic disturbances further impair BCAA utilization.

Glucose interorgan exchange in chronic renal failure

The mechanisms responsible for the altered glucose metabolism observed in chronic renal failure (CRF) were investigated in the postabsorptive state. In 11 patients with CRF and in 15 subjects with normal renal function, the hepato-splanchnic (HS), leg, and brain exchanges of glucose were measured; the HS exchange of gluconeogenic amino acids was also evaluated. Patients with CRF had normal glucose levels, whereas insulin levels and the ratio of insulin to glucose were significantly increased in comparison with controls. In CRF, HS glucose output was slightly lower in comparison with controls (0.46 +/- 0.04 vs. 0.57 +/- 0.04 mmoles/min X 1.73 m2 in controls; P less than 0.1). Arterial levels of alanine and glycine and their uptake by the HS bed were similar in both groups, but in CRF HS serine uptake disappeared, mainly as a consequence of a reduction of its fractional extraction. Conversely, a significant proline extraction became evident, primarily depending on the increased arterial levels of this amino acid. The total HS uptake of potential gluconeogenic amino acids was not different in the two groups, and its ratio to glucose output was increased in CRF (28.0 +/- 4.7 vs. 16.0 +/- 1.9 in controls). In CRF, the arterial-femoral venous differences of glucose were significantly reduced (0.11 +/- 0.04 vs. 0.25 +/- 0.04 mmoles/liter in controls), as was the fractional extraction of glucose in the leg. Finally, in CRF both glucose uptake and its fractional extraction by the brain were unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal ammoniagenesis in an early stage of metabolic acidosis in man

Total renal ammonia production and ammonia precursor utilization were evaluated in patients under normal acid-base balance and in patients with 24-h NH4Cl acidosis by measuring (a) ammonia excreted with urine and that added to renal venous blood, and (b) amino acid exchange across the kidney. In 24-h acidosis not only urinary ammonia excretion is increased, but also total ammonia production is augmented (P less than 0.005) in comparison with controls. By evaluating the individual role of acid-base parameters, urine pH and urine flow in influencing renal ammonia production, it was shown that the degree of acidosis and urine flow are likely major factors stimulating ammoniagenesis. Both urine pH and urine flow are determinant in the preferential shift of ammonia into urine. In 1-d acidosis, renal extraction of glutamine was not increased and the total ammonia produced/glutamine N extracted ratio was higher than in controls (P less than 0.005) and was inversely correlated with the log of arterial bicarbonate concentration (P less than 0.001). In the same condition, renal glycine and ornithine uptake took place; the more severe the acidosis, the greater was the renal extraction of these amino acids (P less than 0.001). These data indicate that at the early stages of metabolic acidosis, in spite of a brisk increase in ammonia production, the mechanisms responsible for the increased glutamine use, which are operative in chronic acidosis, are not activated and other ammonia precursors, besides glutamine, are probably used for ammonia production.

[Activity of renal enzymes producing ammonia from glutamine in the absence of phosphate in the rat: 1. Effect of chronic metabolic acidosis]

Phosphate- independent glutaminase (PIG) and gamma-glutamyl transpeptidase (gamma GT) activities were evaluated in renal cortex homogenates of rats under normal acid-base balance or chronic metabolic acidosis (CMA). An incubation medium containing glutamine 2 mM, no phosphate, pH 7,40, was used. PIG activity was measured as glutamate production and total gamma GT activity as ammonia production. In normal rats gamma GT activity was significantly higher (0,84 +/- 0,05 mumol/min/g wet wt.) than PIG activity (0,48 +/- 0,06 mumol/min/g wet wt.) (p less than 0,01). In CMA there was a significant increase in PIG activity and an even higher increase in gamma GT activity (p less than 0,01 compared to controls in both cases). The glutamate production/ammonia production ratio was 0,57 +/- 0,05 in normal rats, and 0,37 +/- 0,03 in CMA ( p less than 0,025). These data suggest that the increase in PIG activity and, to a further extent, the increase in gamma GT activity may play an important role in augmenting renal ammonia production in CMA.