Benefit of moderate dietary protein restriction on growth in the young animal with experimental chronic renal insufficiency: importance of early growth.

Using a model of unilateral nephrectomy and contralateral heminephrectomy in weanling rats, we studied the effect of severe (6%) and moderate (14%) protein restriction on growth and renal function up to 24 wk of age. One-half the normal (N) and chronic renal insufficiency (CRI) rats underwent a cross-over protocol 6%----14% and 14%----6% at 10wk of age to analyze the contribution of early growth on ultimate wt and length. N or CRI fed a 6% protein diet were the smallest. Animals switched from 6%----14% protein diet did not catch up to their counterparts started on a 14% protein diet (N or CRI). However, N or CRI animals started on a 14% protein diet and switched to a 6% protein diet grew along a curve similar to animals fed a 14% protein diet. Creatinine clearances for CRI rats were not different among the groups. However, protein excretion was highest in those animals completing the study on a 14% protein diet. Growth failure caused by severe protein restriction occurred primarily in the early accelerated growth phase (3-10 wk). We conclude that moderate protein restriction during the early rapid growth phase maintains growth, whereas severe protein restriction is detrimental to growth. Switching to a more restrictive protein intake after the rapid growth phase did appear to offer more renal protection (lower urinary protein excretion) at the end of 24 wk. Severe protein restriction to preserve renal function is a poor strategy for the young rapidly growing individual with chronic renal disease.

Rapid determination of total hydroxyproline (HYP) in human urine by HPLC analysis of the phenylisothiocyonate (PITC)-derivative.

A recent development in the preparation for amino acid analysis is the use of phenylisothiocyanate (PITC) as a precolumn derivatizing agent prior to analysis to form a stable derivative. These derivatives can then be separated by reversed phase high pressure liquid chromatography (HPLC). Because of interest in the accurate measurement of urinary hydroxyproline (HYP), PITC was used for derivatization followed by HPLC analysis. Using an automated computer-controlled sampler system, up to 75 samples can be analyzed each 24 h. Technical details, specificity, and reliability of this method are provided. Duplicate measurements of HYP had a coefficient of variation (CV) of 5.5% and with a recovery of HYP in spiked urine samples of 94 to 104%. A sample frozen and thawed 10 times showed no change in the concentration of HYP. When total HYP was measured in 230 healthy women between 20 and 39 years of age, it was found to be 236.62 +/- 146.41 mumoles/L. These samples were researched in 3.5 days using this technique.

Comparison of whole body and tissue blood volumes in rainbow trout (Salmo gairdneri) with(125)I bovine serum albumin and (51)Cr-erythrocyte tracers.

Total, packed cell and, plasma volume estimates were made for the whole body and selected tissues of rainbow trout by the simultaneous injection of radiolabelled trout erythrocyte ((51)Cr-RBC) and radioiodinated bovine serum albumin ((125)I-BSA) tracers. Blood volumes were estimated with both markers separately by the tracer-hematocrit method and as the combination of the(51)Cr-RBC packed cell and(125)I-BSA plasma volumes. Mean whole body blood volume was significantly less when calculated from the(51)Cr-RBC tracer data (3.52±0.78 ml/100 g; ±SD) than when calculated with the(125)I-BSA tracer (5.06±0.86 ml/100 g) or as the sum of the two volumes combined (4.49±0.60 ml/100 g). The whole body hematocrit (28±5%), estimated as the quotient of the(51)Cr-RBC volume divided by the sum of the(125)I-BSA and the(51)Cr-RBC volumes, also was significantly less than the dorsal aortic microhematocrit (36±4%). Estimates of total blood volumes in most tissues were significantly smaller when calculated from the(51)Cr-RBC data than when calculated by the other two methods. Tissue blood volumes were greatest in highly vascularized and well perfused tissues and least in poorly vascularized tissues. The relative degree of vascularization among tissues generally remained the same regardless of whether the red cell or the plasma tracer was used to calculated blood volume. It is not clear whether the expanded plasma volume is the result of the distribution of erythrocyte-poor blood into the secondary circulation or the result of extravascular exchange of plasma proteins.

HPLC analysis of the phenylisothiocyanate (PITC) derivatives of taurine from physiologic samples.

Taurine is the major free intracellular amino acid. It has become the focus of study by many as a conjugator of bile and as a neurotransmitter and intracellular messenger. In this report we document a technique for measuring taurine in physiologic samples which is rapid, reproducible, and accurate. Any physiologic sample is first derivatized with phenylisothiocyanate (PITC) and separated by reverse phase HPLC, and then taurine is detected by UV at 254 nm. The advantages of this technique for the measurement of taurine are accuracy, small sample size, and reproducibility, and with an automated system many samples can be analyzed.

Estimates of plasma, packed cell and total blood volume in tissues of the rainbow trout (Salmo gairdneri).

1. Total blood volume and relative blood volumes in selected tissues were determined in non-anesthetized, confined rainbow trout by using 51Cr-labelled trout erythrocytes as a vascular space marker. 2. Mean total blood volume was estimated to be 4.09 +/- 0.55 ml/100 g, or about 75% of that estimated with the commonly used plasma space marker Evans blue dye. 3. Relative tissue blood volumes were greatest in highly perfused tissues such as kidney, gills, brain and liver and least in mosaic muscle. 4. Estimates of tissue vascular spaces, made using radiolabelled erythrocytes, were only 25-50% of those based on plasma space markers. 5. The consistently smaller vascular volumes obtained with labelled erythrocytes could be explained by assuming that commonly used plasma space markers diffuse from the vascular compartment.

Beneficial effect of moderate protein restriction on growth, renal function and survival in young rats with chronic renal failure.

We used the model of one-stage uninephrectomy and contralateral heminephrectomy to study the effect of protein restriction on growth and renal function in young (starting age 21 d) female rats. Normal, sham-operated, pair-fed, and chronic renal insufficiency (CRI) rats were fed a 6, 14 or 22% protein (casein) diet. Diets were otherwise isoenergetic and equivalent in sodium, potassium, chloride, phosphate and calcium. Weight, length, urinary protein and creatinine clearances were measured up to 6 mo of age. Regardless of group (normal, sham or CRI), animals fed a 6% protein diet weighed less and were shorter than animals fed 14 or 22% protein diets. No difference in growth could be found between 14 and 22% protein intake. However, animals with CRI fed 22% protein diet had a shorter survival time than animals fed 14 or 6% protein diets. Six percent protein intake led to a lower growth rate over the first 10-12 wk of age than 14 or 22% protein intake. We conclude that 14% protein intake in rats with CRI maintains normal growth and improves survival over 22% protein intake. Rats with CRI fed a 6% protein diet have improved survival compared to rats fed a 22% protein diet but suffer growth retardation.