A method for estimating nitrogen intake of patients with chronic renal failure

A method for monitoring dietary compliance would be useful in treating patients with chronic renal failure (CRF). Nineteen nitrogen balances were measured while patients were eating unrestricted diets containing 6.4 to 15.1 g of nitrogen per day and 14 while patients consumed a 20 to 25 g mixed-quality protein ketoacid-supplemented diet containing 5.2 to 6.6 g of nitrogen per day. Urea nitrogen appearance (U) calculated as the sum of urinary urea nitrogen plus the variation in the body urea pool (using changes in serum urea nitrogen and either the 14C urea space or 60% body weight) was correlated with nitrogen intake (r = 0.84). Both methods gave indistinguishable values for U. Total non-urea nitrogen excretion (NUN) and its components did not correlate with dietary nitrogen. NUN averaged 31.3 +/- 2.1 mg N/kg/day and was not different between the two groups or in patients in neutral compared to those in mildly negative or positive nitrogen balance. Nitrogen balance calculated using estimated U and 31 mg N/kg/day was indistinguishable statistically from measured nitrogen balance. Thus, U varies directly with dietary protein intake and can be estimated using urinary urea nitrogen, SUN, and body weight. Total nitrogen excretion can be estimated accurately as U + 31 mg N/kg/day. From the estimated total nitrogen excretion, dietary compliance of CRF patients in approximately neutral nitrogen balance could be assessed. Furthermore, if nitrogen intake were known, nitrogen balance could be estimated.     

Supplemented very low protein diet ameliorates responsiveness to erythropoietin in chronic renal failure

BACKGROUND: The aim of this study was to evaluate the relationship between uremic state and erythropoiesis in patients with predialytic chronic renal failure (CRF). METHODS: We monitored for 2 years the erythropoietin (EPO) requirement in patients with advanced CRF (creatinine clearance < or =25 mL/min), randomized to either low protein diet (LPD) group (0.6 g/kg body weight/day, N = 10) or very low protein diet (VLPD) group (0.3 g/kg body weight/day, N = 10) supplemented with a mixture of ketoanalogs and essential amino acids, both kept at target hemoglobin levels. RESULTS: The achieved protein intake after 6 months was 0.79 +/- 0.02 g/kg body weight/day and 0.50 +/- 0.02 g/kg body weight/day in LPD and VLPD, respectively; such a difference was maintained up to the end of follow up. The final hemoglobin values did not differ from the basal values in either group (11.5 +/- 0.2 g/dL and 11.5 +/- 0.3 g/dL). EPO dose, that was similar at baseline (62.4 +/- 9.6 UI/kg body weight/week and 61.8 +/- 8.8 UI/kg body weight/week subcutaneously), remained unchanged in LPD but progressively decreased in VLPD down to the final value of 41.2 +/- 7.0 UI/kg body weight/week (P < 0.0001 vs. basal and LPD). VLPD was associated with a decrease of urinary excretion and serum levels of urea nitrogen and phosphate; however, EPO requirement was not correlated with the changes of these parameters. On the contrary, the variation of EPO dose directly correlated with the modification of parathyroid hormone (PTH) levels, that diminished from 229 +/- 55 pg/mL to 118 +/- 16 pg/mL (P < 0.0001) in VLPD and did not change in LPD. CONCLUSION: In patients with advanced CRF, an effective decrease of protein intake of 0.3 g/kg body weight/day induces a reduction of about 35% of the EPO dose required to maintain the target hemoglobin levels. This effect appears dependent on the correction of a moderate secondary hyperparathyroidism.     

Progression of chronic renal failure on substituting a ketoacid supplement for an amino acid supplement.

Twelve patients with severe chronic renal failure (average initial GFR, 13 mL/min) were monitored for 4 to 23 months while receiving an essential amino acid supplement and were then switched to a ketoacid supplement for 6 to 40 months, while continuously receiving a very low-protein (0.3 g/kg), low-phosphorus (7 to 9 mg/kg) diet. Urinary urea N excretion indicated that actual dietary protein intake averaged 0.46 g/kg. Progression, estimated as the linear regression slope of radioisotopically determined GFR on time, slowed from -0.46 +/- 0.31 (SD) to -0.24 +/- 0.15 mL/min/month (P = 0.029). Serum urea N, creatinine, phosphate, and uric acid rose significantly as GFR fell; blood pressure, plasma lipids, and urinary urea excretion were unchanged. Urinary 17-hydroxy-corticosteroid excretion decreased 18%, but this change was only marginally significant (P = 0.087). There was no change in plasma or urinary cortisol or urinary aldosterone. Viewed in light of previous evidence that progression seldom slows when treatment remains constant, the results suggest that this ketoacid supplement slows progression by approximately half, compared with an essential amino acid supplement, with no change in diet.     

Reduction of urea generation and muscle protein degradation by adrenalectomy in acutely uremic rats

The effect of adrenalectomy on the enhanced protein degradation in acute uremia was investigated. Therefore, serum urea nitrogen, urea N appearance and Nt-methylhistidine were followed in bilaterally nephrectomized rats. At 48 h after induction of uremia the animals displayed serum urea nitrogen levels of 223 +/- 9.5 mg/dl as compared to 26.0 +/- 1.0 mg/dl in sham-treated rats. This increment was significantly attenuated in acutely uremic, adrenalectomized animals (176 +/- 6.0 mg/dl). When these rats were substituted with corticosterone (5 mg/kg body weight), serum urea nitrogen readily increased to levels of acutely uremic animals with intact adrenal glands (225 +/- 6.0 mg/dl). The net generation of urea, as determined by the urea N appearance, was significantly increased during acute uremia (370 +/- 26 mg/48 h) as compared to SHAM animals (220 +/- 15 mg/48 h). This increment of urea formation could almost be completely reversed by simultaneous adrenalectomy (238 +/- 20 mg/48 h). When these rats were substituted with corticosterone, the urea N appearance rebounded to values quite comparable to acutely uremic rats with intact adrenal glands (363 +/- 30 mg/48 h). To determine whether skeletal muscle proteins might serve as a source for the enhanced protein degradation in acute uremia, plasma levels of Nt-methylhistidine were measured. Bilaterally nephrectomized rats had Nt-methylhistidine values of 9.6 +/- 1.0 micrograms/ml. In acutely uremic rats without adrenal glands, Nt-methylhistidine levels were found to be significantly decreased (6.0 +/- 0.4 micrograms/ml).(ABSTRACT TRUNCATED AT 250 WORDS)     

The precision of estimating protein intake of patients with chronic renal failure

BACKGROUND: Biochemical methods for estimating protein intake are based on the concept that nitrogen-containing products of protein in diet plus the products arising from endogenous protein are excreted as either urea or non-urea nitrogen (NUN). This formulation is based on the fact that the urea is the principal end product of amino acid degradation and, hence, the urea appearance rate (or net urea production) is parallel to protein intake. The urea nitrogen appearance (UNA) rate is measured as the amount of urea excreted in urine plus the net amount accumulated in body water. A more difficult problem is how to estimate NUN, the sum of fecal nitrogen, and all forms of non-urea urinary nitrogen. Maroni, Steinman, and Mitch (Kidney Int 27:58-65, 1985) proposed estimating nitrogen intake (IN MARONI) from UNA plus NUN excretion rate of 0.031 g nitrogen/kg body weight/day, as they found NUN correlated with body weight but not with dietary nitrogen. Kopple, Gao, and Qing (Kidney Int 27:486-494, 1997) proposed a different equation for estimating nitrogen intake (IN KOPPLE) = 1.20 UNA + 1.74, concluding that dietary nitrogen directly correlates with fecal nitrogen and that NUN is constant for all patients. Their report prompted us to review all nitrogen balance measurements we had conducted in order to address the following questions. Does dietary protein increase fecal nitrogen excretion? Does NUN vary with weight or is it constant? How do the two methods (IN MARONI and IN KOPPLE) compare in estimating dietary protein from UNA? METHODS: We examined nitrogen balance and its components measured in 33 patients with chronic renal failure (CRF) who were eating diets varying from 4.1 to 10.1 g nitrogen/day. We evaluated relationships between dietary nitrogen [intake nitrogen (IN)], NUN, fecal nitrogen, body weight, and the predictability of the two methods. RESULTS: Neither fecal nitrogen nor NUN were significantly correlated with IN (r = 0.04 and r = -0.07, respectively). NUN significantly correlated with body weight (P = 0.008). Measured IN averaged 5.75 +/- 0.41 g nitrogen/day; the estimated IN MARONI value was 5.61 +/- 0.27 g nitrogen/day; the estimated IN KOPPLE was 6.04 +/- 0.44 g nitrogen/day. The prediction errors associated with the IN KOPPLE equation were slightly but not statistically higher than that associated with IN MARONI. CONCLUSION: Fecal nitrogen is not correlated with IN. NUN is not constant but varies with weight, and the traditional method of estimating IN in stable chronic renal insufficiency (CRI) patients from UNA and weight as proposed by Maroni, Steinman, and Mitch is valid.     

Calculated nitrogen balance in hemodialysis patients: influence of protein intake

BACKGROUND: Optimal nutrient intake is important in the maintenance of a positive nitrogen balance in hemodialysis (HD) patients. The objectives of this study were (1) to assess the influence of two levels of protein intakes on nitrogen balance in stable adult HD patients, and (2) to identify a minimum level of protein intake that would result in a negative nitrogen balance, so that preliminary recommendations may be made in Indian patients on maintenance HD (MHD). METHODS: Stable, adult, nondiabetic MHD patients were recruited after informed consent into a cross over trial with a high-protein (HP) diet [1.2 g/kg ideal body weight (IBW)/day), followed by a low-protein (LP) diet (0.6 g/kg IBW/day] after appropriate periods of equilibration; for both diets, 50% of protein was of high biological value, and calorie intake was 35 kCal/kg IBW/day. Duplicate meals and residues were weighed, homogenized, and stored at -20 degrees C for analysis of dietary N by the Kjeldahl method, used to check the consistency of the N content of the diet supplied. Pre- and post- (30-minute equilibrated) blood urea samples were drawn, and details of weights and other HD parameters were recorded. Interdialytic urine collections for urea were obtained. N input came from dietary protein calculated as 16% of the weight of biological protein; N output was calculated using blood-side urea measurements and urinary urea excretion and was the sum of urea N (UN) and nonurea N (NUN) losses (assumed to be equal to 0.031 g N/kg/day). RESULTS: Fifteen patients were recruited. Twelve patients completed both limbs of the study. The mean age was 30.3 +/- 12.7 years. The body mass index was 18.9 +/- 2.4. Serum albumin was 3.8 +/- 0.35 g/dL, and Kt/V (equilibrated) was 1.17 +/- 0.3 g/dL. Protein consumed was 1.06 +/- 0.18 g/kg IBW/day in the HP limb versus 0.61 +/- 0.1 g/kg IBW/day in the LP limb (P = 0.000). Energy intake was 33 +/- 6.5 vs. 32.8 +/- 6. 7 kCal/kg IBW/day, respectively (P = 0.8). The normalized protein N appearance (nPNA) was 0.88 +/- 0.2 g/kg/day in the HP limb versus 0. 78 +/- 0.2 g/kg/day in the LP limb (P = 0.02). Dietary N was 73.5 +/- 15.3 g in the HP week and 42.5 +/- 7.5 g in the LP week (P = 0. 000). The difference between this and the sum of (UN + NUN) losses over the week was 29 +/- 13.2 g versus 1.2 +/- 8.1 g, respectively (P = 0.001), showing a strong, uniformly positive nitrogen balance with HP diet and neutral to negative nitrogen balance with LP diet. The ratio of dietary protein intake (DPI) to nPNA was significantly lower (anabolic) in the HP limb (0.7 +/- 0.2 vs. 1.12 +/- 0.3, P = 0. 000). On a scatter plot of nPNA to DPI, a catabolic relationship was demonstrated below a DPI of 0.75 g/kg/day (95% CI, 0.65 to 0.85 g/kg/day). CONCLUSION: A DPI of approximately 1.1 g/kg/day produces a positive nitrogen balance and 0.6 g/kg/day a neutral to negative nitrogen balance, demonstrating protein anabolism as a function of protein intake. It is suggested that a protein intake of 0.85 g/kg/day should be considered unsafe. These conclusions apply in stable nondiabetic adult HD patients in the setting of adequate dialysis and adequate calorie intake.     

Treatment of chronic uremic patients with protein-poor diet and oral supply of essential amino acids. I. Nitrogen balance studies.

Twenty-six nitrogen balance studies were performed in 15 patients with severe uremia (Ccr mean value 5.1, range 2.3-8.5 ml/min) treated with an unselected protein-poor (16-20 g protein/day corresponding to 2.6-3.2 g N/day) diet and oral supply of the essential amino acids including histidine (2.6 g N/day). The general condition improved and the concentration of serum urea nitrogen decreased. The nitrogen balance, corrected for changes in total urea pool, was negative on the diet alone,-1.46 plus or minus 1.15 g N/day (mean plus or minus SD), but was positive when the essential amino acids were supplied, plus 0.84 plus or minus 0.68 g N/day. In four patients studied after 3 to 26 months of diet and amino acid therapy, during which time a further deterioriation of the renal function had occurred, the nitrogen balance was around zero in three and negative in one patient (-1.2 g N/day). The results show that it is possible with our new regimen to attain positive nitrogen balance or nitrogen equilibrium in severely uremic patients without excessive accumulation of urea in the body fluids.     

Reduction of remnant nephron hypermetabolism by protein restriction

To study the metabolic mechanisms involved in the protective effect of dietary protein restriction on the progression of chronic renal failure, experiments were performed in Sprague-Dawley rats subjected to five-sixths nephrectomy and pair-fed on isocaloric low (4%) protein (LP) or high (50%) protein (HP) diets. Protein restriction reduced the severity of uremia, with lower blood urea nitrogen (BUN) concentrations (8.9 +/- 1.1 v 30.0 +/- 2.9 mmol/L [25 +/- 3 v 84 +/- 8 mg/dL] both n = 12, P less than 0.01), and resulted in lower mortality at 2 weeks (0% v 33%, P less than 0.05), 4 weeks (16% v 58%, P less than 0.05), and 10 weeks (16 v 83%, P less than 0.01). Isolated perfusion of the remnant kidney at 3 weeks demonstrated reduced O2 consumption (QO2) (0.77 +/- 0.2 v 2.56 +/- 0.5 mumol/min/g, both n = 7, P less than 0.05) in the absence of significant differences in inulin clearance (239 +/- 53 v 341 +/- 39 microL/min/g, NS) and net sodium reabsorption (34 +/- 8 v 49 +/- 6 mumol/min/g, NS) in rats fed the LP diet. A lower renal QO2 in protein-restricted animals was also demonstrated in vivo (4.1 +/- 0.9 v 13.8 +/- 2.7 mumol/min/g, P less than 0.01). In vivo P-31 nuclear magnetic resonance (NMR) studies of remnant kidneys did not demonstrate any difference in the steady-state tissue concentrations of adenosine triphosphate (ATP) or inorganic phosphate between rats fed LP and HP diets. Dietary protein restriction decreases the severity of uremia and diminishes renal QO2 in the remnant kidney model.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of acute and chronic protein loading on urinary pepsinogen A excretion

In 8 healthy male volunteers, urinary excretion (UE) and fractional clearance (FC) of pepsinogen A (PGA), beta 2-microglobulin (beta 2-m) and albumin were measured after 6 days high protein diet (HPD; 2.0 g/kg/day) and compared to values obtained after 6 days low protein diet (LPD; 0.5 g/kg/day). In addition, the effect of an acute protein load (APL; 500 g beef) on these variables were measured. Both chronic and acute protein loading induced a rise in glomerular filtration rate (GFR) of about 10% together with a parallel rise in effective renal plasma flow. UE PGA and FC PGA increased both after HPD (UE PGA 1,707 +/- 1,106 ng/min; FC PGA 23 +/- 12%) as compared to LPD (UE PGA 1,200 +/- 987 ng/min, p less than 0.01; FC PGA 18 +/- 12%, p less than 0.05), and after APL (UE PGA 2,276 +/- 1,389 ng/min; FC PGA 26 +/- 16%) as compared to baseline (UE PGA 1,418 +/- 965 ng/min, p less than 0.02; FC PGA 21 +/- 12%, p less than 0.05). UE and FC of beta 2-m and albumin were not affected by protein loading. As PGA is nearly freely filtered, it is concluded that the increase in fractional PGA clearance reflects a decrease in fractional tubular PGA reabsorption. Our results suggest that an increase in fractional protein clearance after protein loading is not necessarily due to an impaired glomerular permselectivity but represents a decreased fractional tubular reabsorption as a result of a GFR-mediated increase in filtered load without a concomitant increase in tubular reabsorption.     

Urinary excretion of oxalate by patients with renal hypercalciuric stone disease. Effect of chronic treatment with hydrochlorothiazide

Hydrochlorothiazide is employed to reduce calcium excretion in patients with urinary stone disease secondary to renal leak hypercalciuria. Because the drug also has been reported to be a competitive inhibitor of oxalate excretion by the renal tubules, we sought to determine whether chronic use indeed affected the amount of oxalate excreted. Patients taking hydrochlorothiazide 50 mg daily did not have a statistically significant reduction in twenty-four-hour urinary oxalate on their customary diets (pretreatment 37 +/- 3 mg/day [mean +/- S.E.M.; N = 22]; at one year 36 +/- 3 mg/day [N = 22]; at two years 37 +/- 3 mg/day [N = 16]). In 12 patients who voluntarily collected twelve-hour urine specimens after dinner on the third day of a low-oxalate diet and again the next day after a 1 g oxalate load, hydrochlorothiazide had no significant effect on oxalate excretion (19 +/- 2.3 mmol oxalate/mol creatinine on hydrochlorothiazide versus 20.6 +/- 2.6 mmol off the drug after low oxalate meal; 50 +/- 7.8 mmol/mol creatinine on hydrochlorothiazide versus 56.2 +/- 7.5 mmol off the drug after an oxalate load). As expected, there was a significant reduction in urinary calcium excretion and thus of calcium oxalate urinary saturation during hydrochlorothiazide administration. Hydrochlorothiazide by itself is not sufficient to reduce oxalate excretion in patients with renal leak hypercalciuria.     

Dietary tryptophan supplementation prevents proteinuria in the seven-eighths nephrectomized rat

Surgical reduction of renal mass in the rat leads to proteinuria, hypertension, and progressive renal failure beyond that of the original physical destruction of renal mass. Both hypertension and proteinuria have been implicated in the process of progression of renal failure. The seven/eighths nephrectomized rats fed a diet supplemented with 4% tryptophan (UT) had a urinary albumin excretion rate of 0.055 +/- 0.056 mg/100 g body weight/hr compared to 0.02 +/- 0.029 mg/100 g body weight/hr in control rats, whereas the nephrectomized rats fed a regular diet (UR) excreted 1.12 +/- 0.730 mg/100 g body weight/hr (P less than 0.001). Hypertension was also prevented in the UT group but not in the UR group. Once hypertension and proteinuria were established during maintenance on a regular diet, they were not reversed by subsequent dietary tryptophan supplementation. If dietary tryptophan supplementation is continued, however, the progressive histopathology that develops after seven-eighths nephrectomy is not prevented despite avoidance of proteinuria and hypertension.     

Effect of low-protein, very-low-phosphorus diet on diabetic renal insufficiency with proteinuria

We describe the clinical outcome of 13 patients with non-insulin-dependent diabetes mellitus (NIDDM), renal insufficiency, and proteinuria, treated for 12.2 +/- 12.9 months (mean +/- SD) with a low-protein, very-low-phosphorus diet (LPVLP) containing 30 g protein and 11.3 mmol (350 mg) phosphorus. After a control period of 18.2 +/- 20.4 months, LPVLP therapy was initiated and serum urea nitrogen, uric acid, and phosphate, as well as urinary excretion of protein, creatinine, urea nitrogen, uric acid, and phosphate, decreased significantly. There was no change in mean blood pressure, hemoglobin, blood pH, and HCO3-, as well as in serum creatinine, protein, albumin, calcium, magnesium, cholesterol, triglyceride, beta-lipoprotein, and high-density lipoprotein (HDL)-cholesterol. Nitrogen balances were measured over 5 weeks in nine patients. Nitrogen balance increased significantly from a negative balance of -0.795 +/- 1.367 g/d in the first week, to almost neutral in the fourth week, and later, was neutral or positive. Neither uremic symptoms nor signs of malnutrition appeared during the LPVLP period. These results suggest that negative nitrogen balance during the initial few weeks does not predict future nutritional status of patients with diabetic renal failure.     

Chronic renal failure accelerates atherogenesis in apolipoprotein E-deficient mice

Cardiovascular mortality is 10 to 20 times increased in patients with chronic renal failure (CRF). Risk factors for atherosclerosis are abundant in patients with CRF. However, the pathogenesis of cardiovascular disease in CRF remains to be elucidated. The effect of CRF on the development of atherosclerosis in apolipoprotein E-deficient male mice was examined. Seven-week-old mice underwent 5/6 nephrectomy (CRF, n = 28), unilateral nephrectomy (UNX, n = 24), or no surgery (n = 23). Twenty-two weeks later, CRF mice showed increased aortic plaque area fraction (0.266 +/- 0.033 versus 0.045 +/- 0.006; P < 0.001), aortic cholesterol content (535 +/- 62 versus 100 +/- 9 nmol/cm(2) intimal surface area; P < 0.001), and aortic root plaque area (205,296 +/- 22,098 versus 143,662 +/- 13,302 micro m(2); P < 0.05) as compared with no-surgery mice; UNX mice showed intermediate values. The plaques from uremic mice contained CD11b-positive macrophages and showed strong staining for nitrotyrosine. Systolic BP and plasma homocysteine concentrations were similar in uremic and nonuremic mice. Plasma urea and cholesterol concentrations were elevated 2.6-fold (P < 0.001) and 1.5-fold (P < 0.001) in CRF compared with no-surgery mice. Both variables correlated with aortic plaque area fraction (r(2) = 0.5, P < 0.001 and r(2) = 0.3, P < 0.001, respectively) and with each other (r(2) = 0.5, P < 0.001). On multiple linear regression analysis, only plasma urea was a significant predictor of aortic plaque area fraction. In conclusion, the present findings suggest that uremia markedly accelerates atherogenesis in apolipoprotein E-deficient mice. This effect could not be fully explained by changes in BP, plasma homocysteine levels, or total plasma cholesterol concentrations. Thus, the CRF apolipoprotein E-deficient mouse is a new model for studying the pathogenesis of accelerated atherosclerosis in uremia.     

Creatine supplementation does not affect kidney function in an animal model with pre-existing renal failure.

BACKGROUND: Creatine is widely used as an ergogenic substance among athletes. Safety of prolonged creatine intake has been questioned, based upon case reports and animal data. We investigated the effect of prolonged creatine ingestion on renal function in animals with normal kidney function or pre-existing kidney failure, respectively. METHODS: Male Wistar rats were randomly allocated to four experimental groups: (i) sham-operated, control diet; (ii) sham-operated, creatine-supplemented diet (2% w/w (0.9+/-0.2 g creatine/kg body weight/day)); (iii) two-thirds nephrectomized, control diet; and (iv) two-thirds nephrectomized, creatine supplemented diet. Glomerular filtration rate was determined using inulin and creatinine clearance, together with albumin excretion, urea clearance, muscle and serum creatine and serum cystatin C concentrations. RESULTS: In contrast to previous reports, no detrimental effects of creatine supplementation on the renal function indices were observed in two-thirds nephrectomized or sham-operated animals. No differences were observed in inulin (0.28+/-0.08 vs 0.25+/-0.08 ml/min/100 g; P=NS) or creatinine clearance rates. Serum cystatin C concentration, urinary protein excretion, and albumin and urea clearance were comparable between creatine-supplemented and control-diet fed animals in both sham-operated and two-thirds nephrectomized animals. Serum creatine and intramuscular total creatine concentrations were higher in creatine-supplemented groups (P<0.05). CONCLUSIONS:Creatine supplementation at a dosage of 2% w/w for 4 weeks does not impair kidney function in animals with pre-existing renal failure or in control animals.     

Urinary excretion of angiotensinogen reflects intrarenal angiotensinogen production

BACKGROUND: In rats maintained on a high salt diet (H/S) to suppress basal renal angiotensinogen levels, angiotensin II (Ang II) infusion for 13 days increased renal angiotensinogen mRNA and protein, thus providing a mechanism for further augmentation of intrarenal Ang II levels. The present study tested the hypothesis that enhanced intrarenal angiotensinogen formation during Ang II infusion is reflected by secretion into the tubular fluid leading to increased urinary excretion of angiotensinogen (UAGT). METHODS: The effects of chronic Ang II infusion were examined on kidney and plasma Ang II levels and UAGT in male Sprague-Dawley rats maintained on an 8% salt diet for three weeks (N=10). Following one week on the H/S diet, Ang II (40 ng/min) was administered for two weeks via an osmotic minipump to one group (H/S + Ang II, N=5), while the remaining rats were sham-operated (H/S + Sham, N=5). Additionally, a control group was prepared with normal salt diet and sham-operation (N/S + Sham, N=5). RESULTS: H/S alone did not alter systolic blood pressure (BP) (103 +/- 2 vs. 104 +/- 2 mm Hg), while Ang II infusion to H/S rats significantly increased systolic BP from 103 +/- 2 to 154 +/- 2 after two weeks. Intrarenal Ang II content in H/S + Ang II was significantly greater than H/S + Sham (435 +/- 153 vs. 65 +/- 14 fmol/g). Ang II infusion significantly increased UAGT (4.0 +/- 0.5 vs. 1.0 +/- 0.2 nmol Ang I/day by radioimmunoassay of generated Ang I; 57 +/- 15 vs. 14 +/- 2 densitometric units by Western blotting analysis) compared to Sham. UAGT by radioimmunoassay was highly correlated with kidney Ang II content (r=0.79); but not with plasma Ang II concentration (r=0.20). CONCLUSIONS: These data demonstrate that chronic Ang II infusion increases urinary excretion rate of angiotensinogen, and suggest that UAGT provides a specific index of intrarenal angiotensinogen production in Ang II-dependent hypertension.     

Protein-restricted diets in diabetic nephropathy

Low-protein diets in nondiabetic renal failure may slow the progressive loss of renal function in some patients, but few studies have detailed the nutritional consequences of these diets in patients with diabetic nephropathy. We studied 7 patients with insulin-dependent diabetes mellitus and chronic renal insufficiency [mean +/- SEM creatinine clearance (S, U): 28.3 +/- 6.5 ml/min (0.47 +/- 0.11 ml/s x 1.73/A)] for 15 weeks who were prescribed a diet of 0.6 g protein/kg ideal body weight. Midarm muscle circumference (24.1 +/- 1.8 at onset vs. 24.5 +/- 1.5 cm at completion), triceps skinfold thickness (21.6 +/- 3.1 vs. 21.0 +/- 1.5 mm), body weight (71.8 +/- 4.1 vs. 71.2 +/- 4.6 kg), and serum albumin [3.0 +/- 0.1 vs. 3.2 +/- 0.1 g/dl (30 +/- 1 vs. 32 +/- 1 g/l)] remained stable. Based on urinary nitrogen excretion, diet diaries overestimated the degree of dietary protein restriction; there was good adherence to the diet as evidenced by a reduction in urinary urea nitrogen (average 32%). Blood glucose control was maintained despite increased carbohydrate intake. On average, creatinine clearance did not change significantly, but proteinuria diminished slightly (1.8 +/- 0.2 vs. 1.5 +/- 0.6 g/day). These results indicate that 0.6 g/kg/day protein diets did not cause protein depletion in insulin-dependent diabetic patients. Longer-term studies are indicated to assess more fully the efficacy of these dietary regimens in reducing proteinuria or benefiting diabetic nephropathy.     

Growth hormone secretion from pituitary cells in chronic renal insufficiency.

To examine whether growth hormone (GH) secretion is adversely affected by chronic renal insufficiency (CRI), the GH secretory response of dispersed anterior pituitary cells perifused with GH-releasing hormone (GHRH) was investigated in 5/6 nephrectomized (CRI, N = 18) and sham-operated (N = 18) rats. Two weeks after nephrectomy, during a period of stable uremia, CRI rats had significantly higher serum concentrations (mean +/- SEM) of urea nitrogen and creatinine than sham rats, 16.8 +/- 1.4 mmol/liter (47 +/- 4 mg/dl) and 79.6 +/- 0.0 mumol/liter (0.9 +/- 0.0 mg/dl) versus 6.1 +/- 0.4 mmol/liter (17 +/- 1 mg/dl) and 35.4 +/- 0.0 mumol/liter (0.4 +/- 0.0 mg/dl), respectively (P less than 0.0001). Incremental gains in body weight and nose to tail-tip length of CRI rats over two weeks were also significantly depressed, 53.3 +/- 5.38 g (CRI) versus 87.0 +/- 3.78 g (sham; P less than 0.0001) and 3.2 +/- 0.2 cm (CRI) versus 3.6 +/- 0.1 cm (sham; P less than 0.05). The cumulative food intake as well as food efficiency (g food consumed/g weight gain) were also adversely influenced by the uremic state: food intake 304 +/- 1 g (CRI) versus 397 +/- 6 g (sham; P less than 0.0001) and food efficiency 0.173 +/- 0.013 g/g of weight gain (CRI) versus 0.219 +/- 0.008 g/g of weight gain (sham). No significant difference in GH secretory rate (ng/min/10(7) cells) was found between the uremic and sham animals under basal conditions, 65.2 +/- 2.1 (CRI) and 67.9 +/- 2.2 (sham) or in response to GH-releasing hormone, 282.8 +/- 42.4 (CRI) versus 306.2 +/- 42.6 (sham).(ABSTRACT TRUNCATED AT 250 WORDS)     

Persistent downregulation of calcium-sensing receptor mRNA in rat parathyroids when severe secondary hyperparathyroidism is reversed by an isogenic kidney transplantation

Experimental severe secondary hyperparathyroidism (HPT) is reversed within 1 wk after reversal of uremia by an isogenic kidney transplantation (KT) in the uremic rats. Abnormal parathyroid hormone (PTH) secretion in uremia is related to downregulation of CaR and vitamin D receptor (VDR) in the parathyroid glands (PG). The aim of this investigation was to examine the expression of CaR and VDR genes after reversal of uremia and HPT in KT rats. 5/6 nephrectomized rats were kept on a normal or high-phosphorus (hP) diet for 8 wk to induce severe HPT (n = 8 in each group). In another group of seven uremic hP rats, uremia was reversed by an isogenic KT and PG were harvested within 1 wk posttransplant. Plasma urea, creatinine, total calcium, phosphorus, and PTH levels were measured. Parathyroid CaR and VDR mRNA were measured by quantitative PCR. Uremic hP rats had significantly elevated levels of creatinine, urea, and phosphorus (P < 0.001) and developed significant hypocalcemia (plasma calcium 1.83 +/- 0.2 mmol/L; P < 0.001) compared with normal control rats. After KT, the levels were normalized from day 3 to 7: creatinine from 0.117 +/- 0.016 to 0.050 +/- 0.002 mmol/L; urea from 23 +/- 4 to 7 +/- 0.3 mmol/L; phosphorus from 3.9 +/- 0.6 to 1.5 +/- 0.06 mmol/L; calcium from 1.8 +/- 0.2 to 2.5 +/- 0.02 mmol/L. Plasma PTH levels fell from 849 +/- 224 to a normal level of 38 +/- 9 pg/ml (P < 0.01). In uremic rats on a standard diet, CaR mRNA was similar to that of normal control rats, whereas VDR mRNA was significantly decreased. In uremic rats kept on hP diet, CaR mRNA was significantly decreased to 26 +/- 7% of control rats (P = 0.01) and VDR mRNA reduced to 36 +/- 11% (P < 0.01). In KT, previously hP uremic rats, both CaR mRNA and VDR mRNA remained severely reduced (CaR, 39 +/- 7%; VDR, 9 +/- 3%; P < 0.01) compared with normal rats. In conclusion, circulating plasma PTH levels normalized rapidly after KT, despite persisting downregulation of CaR and VDR gene expression. This indicates that upregulation of CaR mRNA and VDR mRNA is not necessary to induce the rapid normalization of PTH secretion from hyperplastic parathyroid glands.     

Effect of hyperinsulinemia on urea pool size and substrate oxidation rates

Recently, indirect calorimetry has frequently been used together with hyperinsulinemic clamps. With few exceptions, however, no attention was paid in these studies to the possible effects of hyperinsulinemia on urea nitrogen (N) pool size and the consequences of such changes on the calculated rates of protein, lipid, and carbohydrate (CHO) oxidation. We have determined the effects of euglycemic-hyperinsulinemic clamps on urea N pool size, urinary N excretion, and rates of protein, lipid, and CHO oxidation (measured by indirect calorimetry) in six normal men. Insulin infusion (1 mU.kg-1.min-1) increased peripheral venous insulin concentration from 7 +/- 1.2 (mean +/- SE) to 51 +/- 4 microU/ml. Glucose concentration was clamped at 84 +/- 1.1 mg/dl. Between 0 (preclamp) and 360 min (end of clamp), blood urea N concentration decreased from 17.2 +/- 1.1 to 11 +/- 0.8 mg/dl (P less than .001), and the urea N pool decreased from 604 +/- 41 to 388 +/- 30 mmol (P less than .001). The urea N production rate decreased from 461 +/- 91 (preclamp) to 91 +/- 63 mumol/min during the last 4 h of the clamp (P less than .05). Urinary N excretion remained unchanged (705 +/- 113 vs. 905 +/- 125 mumol/min, NS). Correction of urinary N excretion for insulin-induced reductions in the urea N pool resulted in the following changes in substrate oxidation rates (calculated for the last 4 h of the clamp).(ABSTRACT TRUNCATED AT 250 WORDS)