Relationship between magnesium and zinc levels of the diet and its protein utilization

Protein utilization of the diet was tested in relation to different levels of magnesium and zinc in rats. The experimental diets contained either a low (0.14 g Mg or 10 mg Zn/kg) or adequate (0.45 g Mg or 40 mg Zn/kg) level of Mg or Zn and two different quality protein sources: casein or wheat gluten. Net protein utilization and net protein radio indexes in case of casein were significantly lower for the diet containing a low level of Mg or Zn. For gluten diets, such differences were not observed. Digestibility of protein measured in rats fed a low Mg or Zn casein diet was the same as for the diets with an adequate content of these minerals. Rats fed low Mg or Zn casein diets showed a significantly lower plasma Mg or Zn and a lower liver DNA content in comparison to the rats on adequate Mg or Zn diets. The results indicate that the utilization of protein is affected by Mg and Zn content of the diet and that this relationship depends on the quality of protein.     

Influence of Dietary Protein Concentration and Quality on Response to Erythropoietin in the Polycythaemic Rat

S ummary . The effects were examined of dietary protein concentration and quality on the response of polycythaemic hypertransfused rats to 6 units of human urinary erythropoietin. Rats were either starved or fed one of 14 different diets. Four protein sources were used, having a quality gradient from 100 to about 24. Two proteins—casein and wheat gluten—were used at five different levels of concentration (5–25%) in the diet. The response of rats maintained on the standard diet (Purina rat chow, 23.4% protein/g) was taken as the normal standard. The response to erythropoietin was 25% of normal in starved rats and 35% of normal in rats put on a protein-free diet. When 10% protein in the diet was obtained by using high biological value proteins (egg yolk or casein) the response to erythropoietin was normal. When the same concentration was achieved by using low biological value proteins (wheat gluten or corn protein) the response to erythropoietin was undistinguishable from that of rats put on the protein-free diet. When rats were maintained on diets with different concentrations of casein (5–25%) a normal response was observed when protein concentration was 10% with no further changes at higher concentrations. When rats were fed diets with different wheat gluten concentrations (5–25%) the response to erythropoietin was subnormal. These data suggest that the ability of rats to respond normally to erythropoietin is dependent on a continuous dietary intake of proteins at levels which are dependent on their biological values.     

The effect of quantitative and qualitative protein deficiency on blood regeneration; white blood cells

1. The effect of diets, varying in quantity or quality of protein, on white bloodcell regeneration was studied in leukopenic rats, the leukopenia having been induced by a protein-free diet.

2. Diets containing different amounts of casein (3, 6, 9 and 18 per cent, respectively), were fed ad libitum. At the 3 per cent level, a further decrease occurred ofwhite blood cells, whereas the other three diets initiated a regeneration of leukocytes, its degree being more or less in proportion to the casein content.

3. In experiments with diets containing 18 and 30 per cent of casein, the amountof protein eaten and not its level in diet was the decisive factor in the regenerationof leukocytes. The white blood cell regenerating effect of a diet containing anoptimal level of protein, may be neutralized when given in restricted amounts.

4. Diets containing nutritionally inferior proteins, fed at 9 per cent level, alsoimpaired normal regeneration of leukocytes. The white blood cell regenerationafforded by the proteins investigated was found to increase in the following order:maize, gelatin, wheat, casein, processed soya, peanut, meat, egg.

5. In white blood cell regeneration promoted by dietary protein, granulocyteswere found to react to a greater degree than lymphocytes and monocytes.

     

Increased arginase activity in aorta of mineralocorticoid-salt hypertensive rats

The present study was designed, first to investigate aortic arginase activity during the development and the establishment of mineralocorticoid-salt (DOCA-salt) hypertension, and second, to determine the relationship between arginase activity and blood pressure by giving a protein-supplemented diet (50% casein) known to increase hepatic arginase activity. Our results showed that aortic arginase activity in established hypertension of DOCA-salt rats was higher than in normotensive rats. The protein-supplemented diet (50% casein) accelerated the development of DOCA-salt hypertension. There was a positive correlation between arginase activity and the level of blood pressure in these DOCA-salt hypertensive rats fed 50% casein but not in DOCA-salt hypertensive rats on a normal (20% casein) diet. In normotensive rats, the protein-supplemented diet decreased aortic arginase activity and produced no change in systolic blood pressure. Our data suggest that aortic arginase activity is modified in established DOCA-salt hypertension and could participate in the physiopathology of arterial hypertension.     

Relationship between dietary proteins, their in vitro digestion products, and serum cholesterol in rats

A relationship was assessed between the amino acid composition of 9 protein sources or of their in vitro digestion products and total serum cholesterol in rats. Three animal proteins (casein, beef, fish) and 6 vegetable proteins (soy, pea, peanut meal, rapeseed, oatmeal, wheat gluten) were tested. The intact protein sources were submitted to an enzymatic proteolysis according to a new in vitro digestion method. Each protein source was hydrolyzed for 30 min with pepsin at pH 1.9, then with 10 mg pancreatin at basic pH in a dialysis cell. The digestion products diffused through the dialysis membrane of the cell and were collected by a circulating sodium phosphate buffer over a 6-h period. They were likely to correspond to end products luminal in vivo digestion. The aromatic and the basic amino acids were present in higher proportions in the digestion products than in the intact protein sources, reflecting the specificity of the proteolytic enzymes. Total serum cholesterol was measured on male Sprague-Dawley rats fed cholesterol-free or cholesterol-enriched (1% cholesterol, 0.5% cholic acid) semipurified diets containing protein sources. Total serum cholesterol ranged from 70 mg/dl with the pea diet to 98 mg/dl with the peanut meal diet in rats fed cholesterol-free diets and from 163 mg/dl with the wheat gluten diet to 313 mg/dl with the casein diet in rats fed the cholesterol-enriched diets. These results suggested no specific effect of protein from animal or vegetable origin on total serum cholesterol in rats. In rats fed cholesterol-enriched diets, significant correlations were observed between total serum cholesterol and tyrosine content or leucine/isoleucine ratio of digestion products. These correlations were stronger than those observed with intact protein sources.     

INCREASED ARGINASE ACTIVITY IN AORTA OF MINERALOCORTICOID-SALT HYPERTENSIVE RATS

The present study was designed, first to investigate aortic arginase activity during the development and the establishment of mineralocorticoid-salt (DOCA-salt) hypertension, and second, to determine the relationship between arginase activity and blood pressure by giving a protein-supplemented diet (50% casein) known to increase hepatic arginase activity. Our results showed that aortic arginase activity in established hypertension of DOCA-salt rats was higher than in normotensive rats. The protein-supplemented diet (50% casein) accelerated the development of DOCA-salt hypertension. There was a positive correlation between arginase activity and the level of blood pressure in these DOCA-salt hypertensive rats fed 50% casein but not in DOCA-salt hypertensive rats on a normal (20% casein) diet. In normotensive rats, the protein-supplemented diet decreased aortic arginase activity and produced no change in systolic blood pressure. Our data suggest that aortic arginase activity is modified in established DOCA-salt hypertension and could participate in the physiopathology of arterial hypertension.     

Effect of spinning and additional cross-linking with dialdehyde starch or aluminum ions on the digestibility and quality of casein-Vicia faba protein isolate mixtures

Studies were made in adult rats using an isotopic 15N method. Whole egg, wheat, casein and Vicia faba protein isolate served as reference proteins. The diets were isonitrogenous and feed intake was adjusted to the maintenance energy level. Variations in true N digestibility were small (91.8-96.1%). The amount of metabolic fecal nitrogen in animals receiving the diet containing wheat was 9.4 mg/100 g body weight compared with 4.9-5.8 mg in the other diets. The differences in nutritional quality for maintenance between proteins of plant and animal origin were small. However, spinning (alkaline treatment) and additional cross-linking with aluminum ions or dialdehyde starch affected the nutritional quality for maintenance.     

Effects of soy protein and saponins on serum, tissue and feces steroids in rat

Four groups of rats were fed, for 45 days, one of the following semipurified diets containing sucrose 55% (w/w) and (a) casein 25%, (b) casein 24%, saponins (from Saponaria officinalis) 1%, (c) isolated soy protein 25%, (d) soy protein 24%, saponins 1%. The soy protein diet, compared to the casein one, produced an increase in the fecal excretion of neutral sterols on the 29th and 42nd days, without any modification in the liver, aorta and serum cholesterol concentrations. The effect of soy protein cannot be attributed to its saponin content but other substances associated to soy protein may interfere. With the casein diet, added saponins increased the fecal excretion of neutral sterols and bile acids and decreased liver and aorta cholesterol levels. Serum cholesterol was found unchanged. The effects of saponins were suppressed or greatly reduced with the soy protein diet. These results could be explained by binding of the sterols in insoluble forms.     

Effects of casein and soy protein on hepatic and serum lipids and lipoprotein lipid distributions in the rat

Rats fed a semipurified diet containing casein developed higher levels of circulating triglycerides and cholesterol than animals fed a soy protein-containing diet. The increased serum lipid levels in non-fasted rats were associated largely with the d less than 1.006 g/ml lipoprotein particles (e.g. chylomicrons or very low density-like lipoproteins). In addition, casein-fed rats exhibited higher levels of circulating insulin and depressed hepatic 7 alpha-hydroxylase levels compared to soy-fed rats. Supplementation of the casein diet with arginine, to give an arginine/lysine ratio comparable to that in the soy diet, resulted in a reduction of d less than 1.006 g/ml lipids, a reduction in serum insulin levels and an elevation in hepatic 7 alpha-hydroxylase activity. Supplementation of the soy diet with lysine also resulted in modification of these parameters toward those observed with casein diets, albeit the effects were less dramatic. The results suggest that the hyperlipidemia associated with feeding casein-based diet is associated with decreased rates of clearance of chylomicron-like lipoproteins and their component triglycerides and cholesterol. Furthermore, this is largely prevented by addition of arginine to diets containing casein as the sole protein source.     

Effects of soy components on blood and liver lipids in rats fed high-cholesterol diets

AIM: To assess the effects of soy protein, isoflavone, and saponin on liver and blood lipid in rats that consumed high-cholesterol diets. METHODS: High-cholesterol diets (1%) with or without soy material were fed to 6-wk-old male Sprague-Dawley rats for 8 wk. Blood lipids, liver lipids, glutamic oxaloacetic transaminase (GOT), and glutamic pyruvic transaminase (GPT) levels were measured. The in vitro bile acid-binding ability of soy materials was analyzed. RESULTS: The results of in vitro studies showed that soy protein isolate had a significantly higher bile acid-binding ability (8.4±0.8%) than soy saponin (3.1±0.7%) and isoflavone (1.3±0.4%, P<0.05). On the other hand, at the end of the experimental period, rats that consumed soy protein diets had lower GOT and GPT levels than rats that consumed casein under high-cholesterol diets. Rats that consumed soy protein also had lower total cholesterol (TC) levels in the liver than those that consumed casein under high-cholesterol diets. Rats that consumed the soy protein diet containing both saponin and isoflavone had lower hepatic TC level than those that consumed the soy protein diet without isoflavone alone. The effect of different types of proteins on triglyceride was not significant. CONCLUSION: Consumption of soy provided benefits to control lipid levels under high-cholesterol dieting conditions in this rat model of hypercholesterolemia. The major component that reduced hepatic TC was not saponin, but possibly isoflavone.     

Use of an elemental diet in animals during treatment with 5-fluorouracil (NSC-19893).

Rats eating a diet containing casein hydrolysate (10% wt/wt)(diet 3) instead of whole casein (diet 1) exhibited increased tolerance to nine consecutive daily injections of 15 mg/kg of 5-fluorouracil (5-FU). The relative nutritional efficiency of diet 3 was significantly higher during 5-FU treatment. Serum albumin levels measured after 5-FU treatment dropped by only 2.7% in diet 3 groups and by 13.5% in diet 1 groups. Serum albumin values for rats on the control diet (Purina lab chow) were comparable to those on diet 1. No 5-FU-related mortality was observed in any of the groups. Intestinal brush border enzymes were determined in a group of rats on diet 1. At the end of 5-FU treatment statistically significant changes were observed: sucrase dropped to 30% of control and leucylnaphthylamide-hydrolyzing activity dropped to 19% of control. The activity of gamma-glutamyltransferase did not change significantly. It is postulated that under these circumstances a mixture with a prevalence of free amino acids (casein hydrolysate) could be more readily absorbed than a corresponding mixture containing a larger proportion of oligopeptides.     

Serum lipids, lipoprotein composition and liver cholesterol in genetically obese Zucker rats fed semipurified diets containing either casein or soy protein

The effect of semipurified diets containing either casein or soy protein on serum lipids, lipoprotein composition and liver cholesterol was studied in genetically obese Zucker rats. The ingestion of a cholesterol-enriched semipurified diet containing casein resulted in elevated levels of serum cholesterol and phospholipids compared to the feeding of a soy protein diet. No differences in serum triglycerides were observed. Differences in serum cholesterol and phospholipids were mainly reflected in the very low density lipoproteins and low density lipoproteins and to a minor extent in the high density lipoproteins. Liver cholesterol paralleled the levels of cholesterol in the serum, the rats fed casein exhibited markedly higher levels of liver cholesterol than those fed soy protein. Furthermore, the rats fed casein also had enlarged livers. Thus, this study clearly shows the differential cholesterolemic effect of dietary casein and soy protein in genetically obese Zucker rats.     

Effect of feeding maize/legume mixtures on biochemical indices in rats

Protein-energy malnutrition is one of the major public health problems in developing countries of the world due to prevailing socio-economic problems. This study aimed to observe the effect of formulated complementary blends on biochemical parameters of rats. Extruded complementary blends from maize fortified with cowpea or soybean at a level of 35% and 25% respectively were fed to 4 groups of rats for 28 days. Similarly, 3 other groups of rats were placed on casein, non-protein or rat pellet diet. Biochemical analysis was done on blood samples of the rats. Results from previous studies show the protein content of the formulated diets to range from 15.75% in UMC to 17.24% in MMS. Significantly (p < 0.05) lower WBC, Hb, MCHC, total protein, albumin and globulin values were recorded for the rats fed a non-protein diet (NP). The serum AST level was 75.5, 71.2, 63.2, 51.0, 60.5 and 55.7, respectively, for rats on casein, rat pellet, MMS, UMS, MMC and UMC (list of abbreviations is shown in the appendix) diets. Alkaline phosphatase was significantly (p < 0.05) higher in soybean-based diets while cholesterol was lowest in rats fed the non-protein diet (NP). The value obtained for serum electrolyte concentration in the rats fed NP compared well with rats on other diets but, however, had a significantly (p < 0.05) higher serum sodium value. These results confirm that the experimental diets supported growth, as shown in a previous study, and had no harmful consequence.     

Utilization of [1-14C]carbon of glycine of high glycine diet fed young and old rats

The incorporation of radioactivity from [1-14C]glycine was studied into various organ (serum, liver, muscle) fractions (acid soluble, proteins, lipids, liver glycogen) and carbon dioxide in rats fed with isonitrogenous isocaloric purified diets. The diets contained 30% casein (control), gelatin (exchange of half of the 30% casein) or glycine (corresponding level of glycine in relation to the gelatin diet). The incorporation of radio-activity into proteins was reduced by feeding high glycine diets in young (20-weeks-old) and old (18-month-old) rats in relation to the control diet. The modifications of the results for old animals may be partially explained on the base of a reduced protein turnover rate and adaptation to a high gelatin (glycine) diet.     

Soybean protein-dependent changes in triacylglycerol synthesis and concentration of diacylglycerol in the liver microsomes of fasted-refed rats.

Effects of soybean protein, casein and whole egg protein on various indices for lipid biosynthesis in the liver were compared in fasted-refed rats. Soybean protein compared to casein and whole egg protein significantly reduced activities of glucose 6-phosphate dehydrogenase and fatty acid synthetase. The protein source also slightly reduced the activity of the malic enzyme. Soybean protein compared to other proteins not only reduced the microsomal triacylglycerol but also phosphatidylcholine syntheses when the activities were measured with endogenous diacylglycerol substrate. The protein-dependent changes disappeared, if artificial dispersion of dioleoylglycerol was employed as a substrate. The concentrations of microsomal diacylglycerol and triacylglycerol in whole liver in rats fed soybean protein were lower than those fed other proteins. When the diets containing soybean protein and casein were supplemented with DL-methionine (0.5 and 0.3%, respectively) to meet the nutritional requirement of the animals, soybean protein-dependent reductions in these indices for lipid biosynthesis were still detectable but considerably attenuated. Thus, it is plausible that a soybean protein-dependent decrease in fatty acid synthesis reduced the availability of microsomal diacylglycerol substrate for triacylglycerol synthesis and in turn modified hepatic triacylglycerol concentration. The dietary availability of sulfur amino acids may, at least in part, be responsible for the consequence observed in the present study.     

Diets containing salmon fillet delay development of high blood pressure and hyperfusion damage in kidneys in obese Zucker fa/fa rats

Hypertension is the leading risk factor for cardiovascular and chronic renal diseases, affecting more than 1 billion people. Fish intake is inversely correlated with the prevalence of hypertension in several, but not all, studies, and intake of fish oil and fish proteins has shown promising potential to delay development of high blood pressure in rats. The effects of baked and raw salmon fillet intake on blood pressure and renal function were investigated in obese Zucker fa/fa rats, which spontaneously develop hypertension with proteinuria and renal failure. Rats were fed diets containing baked or raw salmon fillet in an amount corresponding to 25% of total protein from salmon and 75% of protein from casein, or casein as the sole protein source (control group) for 4 weeks. Results show lower blood pressure and lower urine concentrations of albumin and cystatin C (relative to creatinine) in salmon diet groups when compared to control group. Morphological examinations revealed less prominent hyperfusion damage in podocytes from rats fed diets containing baked or raw salmon when compared to control rats. In conclusion, diets containing baked or raw salmon fillet delayed the development of hypertension and protected against podocyte damage in obese Zucker fa/fa rats.     

Effects of diet and metoprolol on lipid levels in the blood plasma and morphology of the heart and intramural branches of coronary arteries of spontaneously hypertensive male rats. A 9-month study

Semipurified diets containing 0.5% cholesterol were used in a 9-month study with spontaneously hypertensive male rats to characterize the effects of the protein source (casein vs. soybean protein), and the selective beta 1-adrenoceptor antagonist metoprolol on both lipid levels in blood plasma and the aorta, and on the morphology of intramural branches of coronary arteries. Raised blood lipid levels were observed in these rats. A significant decline in HDL2 cholesterol took place, while plasma cholesterol belonging to lipoprotein fractions of lower density increased. Metoprolol treatment led to a substantial elevation of the plasma triacylglycerol level and, with time, a reduced cholesterolemic response. The use of soybean protein instead of casein had a persistent plasma lipid-lowering effect. Arteriosclerotic changes in the form of musculo-elastic thickenings, intimal cushions and homogeneous hyalin deposits appeared in the intramural coronary arteries of rats in all groups after 9 months on the diet. However, intimal deposition of lipid was only present in rats belonging to the casein group not treated with metoprolol. Rats of this group also showed more severe myocardial lesions in the form of scar tissue with or without inflammatory cell reaction.     

Effects of soy protein hydrolysate on blood pressure and angiotensin-converting enzyme activity in rats with chronic renal failure

We investigated the effects of soy protein and soy protein hydrolysate on blood pressure control, angiotensin-converting enzyme (ACE) activity, and renal function in a rat chronic renal failure model. Rats that had undergone a 5/6 nephrectomy were separated into three groups and fed different experimental diets for 14 weeks. At the end of the study, rats that fed a diet containing soy protein as the protein source had better blood pressure control and renal function, as well as lower circulating ACE activity and renal tumor-necrosis factor-alpha (TNF-alpha) concentration than rats fed a casein protein diet. Soy protein hydrolysate was shown to be as effective as soy protein in preventing the elevation of blood pressure, the progression of renal failure, and decreases in kidney TNF-alpha level, plasma ACE activity, and insulin concentration. In conclusion, the beneficial effects of consuming soy protein on blood pressure and renal function may be mediated mostly by its pepsin-digested hydrolysate through its ACE inhibitory activity.     

The effects of dietary fat and protein levels fed to Syrian hamsters early in life,on blood chemistry throughout life

Nine experimental diets, composed of three levels of protein as casein (9, 18 and 36 g/385 Kcal) and three levels of fat as corn oil (4.5, 9.0, and 18.0 g/385 Kcal), were fed to weanling Syrian hamsters from 3–8 weeks of age. The control diet, consisting of the medium levels of casein and corn oil, was fed for the remainder of life. Blood was collected at 0, 1, 3, 6, 12, and 18 months for analysis of several indicators of nutritional status. Whole blood hemoglobin rose between 0 and 3 months, and then declined. Female values were lower than those of males, and the high fat diet increased hemoglobin at 6 months (5 months after the diet change). High protein diets increased hemoglobin values at 1 month, and decreased hemoglobin at 18 months. Serum triglycerides declined with age to 12 months. Feeding high protein diets resulted in the highest circulating triglycerides at 1 month and the lowest at 18 months. Feeding the high fat diets resulted in elevated triglycerides at 1 and 3 months. Plasma glucose levels increased between weaning and 6 months, then declined to 12 months. High fat diets led to elevated plasma glucose at 1, 3 and 6 months in animals fed the high protein levels, but at only 1 and 6 months in animals fed the low levels of protein. Serum albumin was consistently higher in male hamsters, and serum globulins in the females. Changes in the serum protein fractions with age differed for each of the fractions. Serum alpha one globulins increased with dietary protein, and serum beta globulins increased with dietary fat at 1 month.     

The effect of quantitative and qualitative protein deficiency on blood regeneration; hemoglobin

1. The effect of diets, varying in quantity or quality of protein, on hemopoiesiswas studied in protein depleted and anemic adult rats.

2. In experiments with diets containing different amounts of casein (0, 3, 9 and18 per cent, respectively), and fed ad libitum, it was found that with a protein-freediet a further decrease of hemoglobin occurred, whereas the other three dietsinitiated a regeneration of hemoglobin; its degree being more or less proportionalto the casein content.

3. In experiments, in which diets with 9 and 18 per cent of casein, respectively,were given in restricted amounts, it was found that the degree of hemoglobinformation was similar to that with the same diets when given ad libitum, whereasthe weight gain was considerably less. It is concluded, therefore, that in caloricdeficiency hemoglobin formation has a priority over weight recovery.

4. A diet containing 30 per cent casein and given in restricted amounts induceda further weight loss, whereas the concentration of hemoglobin showed a markedincrease. Comparing the results obtained by this diet with those observed with 18per cent casein diets, given either ad libitum or in controlled amounts, it was evident that restriction of the quantity of food protein interferes more seriously withhemopoiesis than restriction of calories.

5. Diets containing nutritionally inferior proteins fed at 9 per cent level, alsoimpaired normal hemopoiesis. Hemoglobin regeneration induced by the proteinsinvestigated was found to decrease in the following order: eggs, meat, processedsoya, casein, peanut, maize, wheat, gelatin.

6. Comparing the nutritive value of various proteins for regeneration of hemoglobin and of granulocytes it was found, that casein and soya and maize proteinsare considerably more efficient for hemoglobin formation than for production ofgranulocytes, whereas wheat protein and gelatin have a higher granulocytopoieticcapacity.