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.     

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.     

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.     

Nutritional effects on the lifespan of Syrian hamsters

Syrian hamsters were fed one of nine semipurified diets composed of three casein levels (9, 18, and 36 g/385 Kcal), with each of three corn oil levels (4.5, 9.0, and 18.0 g/385 Kcal). These diets were given either for five weeks and were followed by control diet (18 g casein and 9 g corn oil/385 Kcal) or control diet was fed for the first five weeks and was followed by the nine diets. Calorie consumption, maximum body weight and length of growth period and of life are reported. Calorie consumption was directly related to dietary fat levels. Maximum body weights increased with increasing dietary fat and protein when the various diets were fed during weeks 1–5. This result was not due to a conditioning of the animals fed high-fat or high-protein levels during weeks 1–5 to consume more calories after week 5, since after this time consumption was the same in all groups fed the control diet. When diets were fed from week 6 body weight increased in both sexes with increased dietary fat; however, higher dietary protein increased female and decreased male maximum body weight. Males took longer to reach these maximum weights than females, and were not affected by receiving the various diets during weeks 1–5. However, when diets were fed from week 6 until death, the growth period increased with higher dietary fat or protein. Male hamsters survived longer than females with each experimental treatment. Animals fed low-fat, low-protein diet or high-fat, high-protein diet during the first 5 weeks of the study survived longest. When diets were fed from 6 weeks until death, survival increased as dietary fat rose for both sexes. In contrast, survival improved as dietary protein rose for females or decreased for males. These studies establish a basis for further investigations on the link between nutrition and longevity in the Syrian hamster.     

Effects of protein deficiency and rehabilitation on growth and tissue composition in growing rats

The objective of the present work was to study the influence of protein quantity and quality on some biochemical parameters in the liver, brain and plasma of rats at 51 days of age. This profile was sketched through the weight of the liver and brain and their content of DNA, RNA and protein and through the total amount of protein, the ratio NE/E and the activity of transaminase GOT and GPT in the plasma. During gestation and lactation, diets of 20% casein, 8% casein and 8% corn were used. At weaning, five experimental groups, with and without nutritional recuperation, were established. As a result, it was observed that the groups fed on a hypoprotein diet (8% casein or 8% corn) were the most seriously compromised in body weight and biochemical parameters with the group fed on corn being the most seriously affected. The animal which were recuperated nutritionally presented a net improvement in all of the parameters. However, the values describing the development of the body and organs in these groups remained inferior to those obtained in the control group. The success of reversibility will depend on the phase of development during which malnutrition occurred and the duration and intensity of the original deficit and the subsequent rehabilitation treatment. Organs in a phase of accelerated development will be especially sensitive to the irreversible effects of malnutrition.     

Marginal protein deficiency in pregnant rats. Changes in offspring body composition

The influence of protein on some biochemical parameters in the liver, brain and plasma of rats at weaning was studied. The tissue parameters studied were the amounts of DNA, RNA and protein in the liver and brain. For the plasma, the parameters studied were the total amount of protein and the ratio of non-essential to essential amino acids (ratio NE/E). During the gestation and lactation period, the rats were divided into three groups according to the diet received: group 1, 20% casein; group 2, 8% casein; and group 3, 8% corn. As a result we can assert that groups 2 and 3, fed on hypoprotein diets, were seriously compromised in body weight and in the biochemical parameters and these alteration were enhanced by the corn diet. These results suggest that the alterations depend on the duration and intensity of the malnourishment and that the quality of the protein is an important factor to be considered.     

Dietary protein, fat, and minerals in nephrocalcinosis in female rats.

Young female rats fed semipurified diets containing casein or a soy protein isolate had extensive nephrocalcinosis at the junction between the outer and inner stripe of the outer medullary zone after 5 wk on the diets, whereas rats fed a diet containing a lactalbumin concentrate did not. Although the percentages of actual protein and of total ash were similar in all three diets, the concentrations of individual minerals were not, owing to methods used in isolating the proteins. Comparison of the individual mineral contents of these diets with those in other laboratories as compiled from the literature suggested that factors other than minerals, including protein, are also implicated. Dietary fat appeared to be another such factor in a series of experiments in which saturated medium-chain triglycerides and corn oil were included in diets containing soy protein isolate. Although these diets had identical mineral compositions, the rats fed medium-chain triglycerides had less severe lesions.     

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.     

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.     

An imbalance in the methionine content of the maternal diet reduces postnatal growth in the rat

The pregnant rat fed a low-protein diet has become widely used as a model system in the study of the prenatal programming of adult metabolism and disease. When pregnant rats of the hooded Lister strain were fed semisynthetic diets containing 18% or 9% casein supplemented with 0.5% dl-methionine, there was significant postnatal mortality in the group fed the low-protein diet. In a second experiment, dams were fed diets containing 9% casein supplemented with varying concentrations of dl-methionine up to 0.4% (w/w) and compared with a group fed a diet containing 18% casein supplemented with 0.5% dl-methionine. At birth, the pups from dams fed the low-protein diets supplemented with 0.2% dl-methionine or greater were significantly smaller than those of the dams fed the diet containing 18% protein. By 25 weeks of age, the body weight of the offspring of dams fed the low-protein diet supplemented with 0.2% or 0.3% dl-methionine were approximately 10% lower than those in the control group of offspring from dams fed 18% protein supplemented with 0.5% dl-methionine. There were corresponding changes in the weights of the major organs. These data suggest that increasing the dl-methionine supplement in the low-protein diet retards the growth of the fetus and affects the mature adult body weight. In contrast to the findings of other studies that used different formulas of the low-protein diet, the glucose tolerance in the offspring was unaffected by the protein content of the maternal diet at all levels of dl-methionine supplementation. These results suggest that the changes in metabolism of the offspring result from interactions between protein, lipids, and carbohydrates in the maternal diet, rather than a consequence of postnatal growth retardation per se and highlight the importance of considering all components of the maternal diet in the programming mechanism.     

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.     

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.     

Mechanisms of thermogenesis induced by low protein diets

Weanling (22-day-old) rats fed a low protein (8% casein) diet consumed the same amount of energy as controls (22% casein diet), but intake corrected for body size (kJ/kg0.75) was increased in the former group. Weight gain and the efficiency of gain (g gain/MJ) were markedly reduced in low protein fed rats. Resting oxygen consumption (VO2) was elevated by 15% in the low protein group but this difference was completely abolished by beta-adrenergic blockade with propranolol. Interscapular brown adipose tissue (BAT) mass, protein content, mitochondrial yield and GDP binding were increased in low protein fed rats but mitochondrial alpha-glycophosphate shuttle activity of BAT was unaltered, although shuttle activity was elevated in liver mitochondria. Plasma triiodothyronine levels were increased by 64% in the low protein group, whereas insulin levels were markedly reduced in spite of normal blood glucose levels. Resting VO2 and BAT mass were also increased in older (55-day-old) rats fed the low protein diet, but the changes were smaller than in weanling rats. These data suggest that the decreased metabolic efficiency seen in rats fed protein deficient diets involves sympathetic activation of BAT, and is therefore similar to the thermogenic responses seen in cold adapted and cafeteria-fed animals.     

Fish protein stimulated the fibrinolysis in rats

OBJECTIVE: We hypothesized that fish protein affects blood coagulation and/or fibrinolysis, and compared the activity and amounts of factors involved in blood coagulation and fibrinolysis in rats fed the fish protein, which was treated to remove water-soluble and ethanol-soluble elements, from sardine (sardine protein). METHODS: In the first experiment, rats were fed for 21 days an AIN-93G-based control diet, and diets in which the casein of the control diet was exchanged for sardine protein at 5, 10 and 20% levels. In the second experiment, rats were fed an AIN-93G control diet and diets containing 5% fish oil, 10% sardine protein or both (5% fish oil + 10% sardine protein) for 21 days. At the end of the experiments, blood coagulation time, hemostatic parameters and fibrinolysis parameters were measured. RESULTS: The activated partial thromboplastin time (APTT), which is an assay for blood coagulation time in the intrinsic blood coagulation pathway, of rats fed the 20% sardine protein diet was significantly prolonged compared to that of rats fed the control diet. The prolonged APTT by dietary sardine protein was due to a significant decrease of the activities of plasma blood coagulation factors VIII, IX, XI and XII. On the other hand, dietary sardine protein significantly increased the activity of tissue-type plasminogen activator, and the amount of plasma plasmin-alpha(2)-plasmin inhibitor complex, which are markers of activated plasmin. Moreover, we observed that the 20% sardine protein diet increased the amount of plasma D-dimer, which is a degraded product of the fibrin polymer by plasmin. In the second experiment, the APTT and PT of rats fed the F diet were prolonged compared to those of rats fed the control diet, however the concentration and amount of fibrinolytic parameters in the plasma were almost the same as those of rats fed the control diet. In contrast, the F+S diet not only prolonged APTT and PT, but also increased the concentration and amount of fibrinolytic parameters in plasma. CONCLUSIONS: We consider that the beneficial effects to health and amelioration of cardiovascular and cerebrovascular diseases by fish consumption are caused by a combination of the suppressing effect on blood coagulation of n-3 polyunsaturated fatty acids and the promoting effect on fibrinolysis of fish protein.     

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.     

Lack of effect of cerulein on pancreatic growth of rats fed a low-protein diet.

The effect of dietary protein deficiency and protein concentration of the diet on the pancreatic trophic response to a CCK analogue (cerulein) were studied. Rats were fed for 14 days with semipurified diets containing 5, 30, or 60% casein. During the final 4 days, they received 2 micrograms/kg cerulein or gelatin vehicle subcutaneously three times/day, and the effects on pancreatic weight and pancreatic content of protein, RNA, DNA, amylase, and chymotrypsin were determined. Cerulein failed to increase significantly any pancreatic parameter in rats fed 5% casein, while stimulating significant increases in almost all parameters in rats fed 30 and 60% casein diets. In the absence of cerulein treatment, increases in dietary protein levels caused progressive increases in all pancreatic growth parameters with the exception of amylase. In the presence of cerulein, increases in dietary protein concentrations caused progressive increases in pancreatic growth parameters (except amylase), which were maximal at 30% casein concentration of the diet for most parameters. The results confirm that pancreatic growth is stimulated by increasing protein concentration of the diet and indicate that a low protein diet, acting through a deficiency of dietary nitrogen and essential amino acids, limits the pancreatic trophic response to CCK or analogues. These results explain the failure of trypsin inhibitors to stimulate pancreatic growth in rats fed low levels of dietary protein.     

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.     

Differential effects of cooked beans and cooked lentils on protein metabolism in intestine and muscle in growing rats

AIMS: The effect of diets based on cooked beans or lentils on protein metabolism in intestines and muscles was studied in rats. METHOD: The cooked seeds were used as the unique protein source in balanced diets (containing 229 and 190 g of crude protein per kg dry matter) fed to young growing rats for 20 days. Their effects were compared with those of the control casein diet in pair-fed rats. Protein synthesis rates in small and large intestines and in gastrocnemius and soleus muscles were determined in vivo, in a fed state, by the flooding dose method, using 13C-valine. RESULTS: In the small and large intestine tissues of the legume fed groups, protein, RNA relative masses (mg.100 g BM(-1)) and protein synthesis rates (FSR and ASR) were higher than in the control rats (p < 0.05). In gastrocnemius and soleus muscles,protein and RNA contents (in mg) and protein synthesis rates were significantly (p < 0.05) lower in the legume-fed groups than in the control rats. CONCLUSION: The chronic intake of cooked legumes increased protein synthesis rates in intestinal tissues and decreased them in muscles. This effect was greater for beans than for lentils in the large intestine and in gastrocnemius muscle.     

Effect of protein malnutrition on glycoprotein, protein and lipid synthesis in the rat cerebellum during the period of brain growth spurt

Female Wistar rats were fed a normal-protein diet (25% casein) or a low-protein diet (8% casein) during pregnancy and lactation. The two diets were isocaloric and contained appropriate amounts of mineral salts and vitamins. Pups from dams submitted to the low-protein diet had a lower body weight than normally fed controls as early as on the day of birth, but a difference in cerebellar weight between the two groups was observed only on the 15th postnatal day. Malnutrition had no effect on cerebellar protein concentration, which increased with age in both groups. The cerebellar DNA concentration was higher at 7 and 15 days of age in normally fed rats than in malnourished rats, whereas at 21 days of age it was higher in the malnourished animals. [U-14C]Leucine and [2-3H]mannose incorporation into proteins and lipid synthesis from acetyl coenzyme A (CoA) derived from [U-14C]leucine markedly decreased with age in the cerebellum of rats fed both diets. [2-3H]Mannose incorporation into cerebellar glycoproteins was greater in malnourished rats during the period of brain growth spurt than in normally fed rats at all ages studied. Prenatal and postnatal protein malnutrition had no effect on [U-14C]leucine incorporation into cerebellar proteins or on cerebellar lipid synthesis from acetyl-CoA derived from [U-14C]leucine during the period of brain growth spurt.     

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.