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Sources of casein protein and wheat gluten were analysed for the content of proteins, fats, saccharides, water and amino acids. The chemical score of the amino acids and the ratio of essential and non-essential amino acids (E/N) were determined. In rats (males) at the age of 120 days, given the diets for 14 days, the optimal and maintenance physiological daily rations were determined from the changes of body nitrogen, body water and weight dependent on the protein intake, using the method of increasing casein protein and wheat gluten content from 0 to 40 per cent in the diet. In 120-134-day-old rats, the optimal daily dose was 1.75 g of casein protein (7.5 per cent of all proteins in the diet) and 2.46 g of wheat gluten protein (10 per cent of all proteins in the diet). As to the maintenance rations determined from the weight changes, body nitrogen and body water in dependence on the protein intake, in these rats the successive daily rations were 1216 mg, 1214 mg and 1302 mg for the casein protein, and 1731 mg, 1760 mg and 1861 mg for the wheal gluten protein.

Male Norway rats of the Wistar strain, aged 30, 75, 90, 150, 180, and 360 days, were given ad libitum diets with optimum nutrient contents at every age. Determining the net protein utilization, the values of protein retention were calculated from protein intake. The energy demand per unit of protein retention was determined from the saccharide and fat intake. The energy ratios of proteins, fat, and saccharide were calculated from the optimum nutrition values; this ratio was 13:(57-29):(30-58) in the period of rapid growth (30-90 days old animals). 12:28:60 in the period of maturing (slower growth, 150 days old animals), and 10.5:28:61.5 at maturity (finished growth, 180-360 days old animals). The daily weight gains of the animals given optimum diets (5.52, 5.22, 5.09-3.73-2.11, 1.85 g daily) and the values of protein retention also corresponded to the division of the animals according to their growth (after administration of the standard Larsen diet). In the period of rapid growth, protein retention was increasing up to the age of 90 days--this suggests that the proteins are utilized for building the body and for its development. A decrease in protein retention in 150 days old animals means that the animals have entered the stage of slow growth. Finally, the low retention values at adult age suggest that the proteins are utilized only for the regeneration of worn tissues and for maintenance. It is indicated by the higher values of energy demand per unit of body protein retention at adult age that more energy (mainly the energy of saccharides--starch) is needed to secure the processes of tissue maintenance and regeneration.

Male rats (Wistar strain, Velaz, Prague) aged 30, 90 and 150 days were fed 14 days ad libitum on a high fat diet (containing 40% margarine) and their growth (PER, NPR) and utilization (NPU, LPU) parameters of protein (casein) biological value were compared with those of animals given a standard gel containing 10% margarine (the diets were isoenergetic). The course of gluconeogenesis in their liver was also determined by measuring phosphoenolpyruvate carboxykinase (PEPCK) activity. A high fat intake had a negative effect on the growth parameters of protein biological value, PER and NPR, in all three age groups and on the utilization parameters NPU and LPU in 30- and 90-day-old rats. The nonsignificant increase in NPU and LPU in the oldest animals was evidently related to the equal protein intake compared with the control, indicating that proteins need to be utilized more economically in the presence of a raised fat intake; owing to their far lower fat intake compared with 90-day-old animals on a high fat diet, the fat had a less negative effect on their protein utilization than in the younger age group. The negative effect of a high fat intake was confirmed by high activation of gluconeogenesis in 30- and 90-day-old animals and by raised phosphoenolpyruvate carboxykinase activity in 150-day-old rats, in which the supposition that gluconeogenesis would be highly activated if the diet were administered for a period other than 14 days cannot be ignored. The biological and biochemical methods employed in this study can be used with a wider perceptual range of dietary nutrients to determine optimum nutrient values under different conditions.

Low-protein (5%) and high-protein (40%) diets as well as low-fat (5%) and high-fat (40%) diets were fed to weanling rats in a 14-day experiment, the standard diet containing 10% of protein and 10% of fat. The net protein utilization of casein, the liver protein utilization and the activity of the key enzyme of gluconeogenesis in the liver, phosphoenol pyruvate carboxykinase, were determined. The utilization of proteins by the organism was adversely affected by a high intake of proteins and also of fats. This fact and the observed stimulation of gluconeogenesis testify to the physiological and economical unsuitableness of diets containing excessive amounts of proteins and fats. A low fat intake was less detrimental to the utilization of proteins than a high fat intake; a low intake of proteins seemed to improve the utilization, but other parameters evidenced that it is not sufficient. The application of diets with closely graded contents in wide ranges for various times will yield biochemical indicators being of importance as supplementary factors in the determination of the physiological value of nutrients under different conditions.

Six-month-old male rats were given diets with mounting casein and wheat gluten protein concentrations from 0% to 40% and after 14 days the optimum and minimum physiological doses were determined from changes in body nitrogen, body water, body weight and protein intake. The optimum dose for casein protein was 1.54 g/d (5% protein in the diet) and for wheat gluten protein 2.10 g/d (7.5% protein in the diet). The minimum casein and wheat gluten protein doses for 180- to 194-day-old rats, determined from body nitrogen changes, were 1499 mg/d (4.86%) and 1995 mg/d (7.12%) respectively, from body water changes 1561 mg/d (5.06%) and 2027 mg/d (7.23%) and from body weight changes 1333 mg/d (4.32%) and 1951 mg/d (6.06%). It should be noted that, unlike younger animals aged 35-49, 75-89 and 120-134 days, the optimum and minimum doses for six-month-old rats were approximately the same.

SPF male Wistar rats weighing 250-260 g and aged 90 days were fed 14 days on diets with a constant 10% protein (casein) content, a constant 11% fat (margarine) content and mounting saccharide (rice starch: sugar: potato starch - 6.4: 1.2: 1) contents of 31, 36, 41, 46, 51, 56, 61 and 66%. Protein intake and the body and liver nitrogen values were used to determine the utilization parameters of protein biological value, i.e. NPU (body) and LPU (liver), for the individual diets. Liver gluconeogenesis was also studied by measuring specific phosphoenolpyruvate carboxykinase (PEPCK) and fructose-1.6-diphosphatase (FDP-ase) activity. On the basis of linearity between the growth parameter NPR and protein and saccharide intake we determined the reciprocal relationship of the intake of the two nutrients and used it to compute the optimum saccharide concentration for the diet. The 51% saccharide diet gave the best protein utilization (the maximum (net) protein utilization value) in the 90-day-old rat organism. This was confirmed by the course of gluconeogenesis, which was significantly activated in the presence of 31-46% saccharide diets. By substituting the optimum protein intake in the reciprocal saccharide-protein intake relationship we obtained the optimum saccharide intake, which corresponded to a 49% concentration in the diet. With its use of a biological, biochemical and computation method, the study is a contribution to the determination of optimum nutrient values.

Over a 14-day period, male SPF Wistar rats with an initial weight of 60, 200 and 250 g (ages 30, 75 and 90 days) were given diets with a constant protein content (10% casein) and a mounting fat content (10, 15, 20, 25, 30, 40 and 50% margarine, at the expense of the saccharides in the standard diet). The utilization parameter of protein biological value (NPU) for the various diets was determined from protein intake and the body nitrogen values. The reciprocal relation of the intake of the two nutrients was determined on the basis of linearity between th growth parameter NPR and protein and fat intake and, after substituting the optimum protein intake, was used to compute the optimum fat content of the diet. From the aspect of the maximum NPU value the optimum fat contents were 30% for 30-day-old, 15% for 75-day-old and 10% for 90-day-old animals. In all three age groups (according to the growth curve for the standard Larsen diet animals with an equal growth rate of 3 g/day), protein utilization under optimum nutritional conditions was the same. The optimum fat content of the diet computed from the reciprocal relationship of fat and protein intake is in agreement with the value obtained by the biological method - 29.4% (49.5 energy %) for 30-day-old animals, 15,8% (30.4% of the total energy value of the diet) for 75-day-old animals and 11.83% (23.7% of total energy) for 90-day-old rats. By using a biological and a mathematical method, this study contributes to the determination of optimum physiological doses of nutrients.

Using mounting casein and wheat gluten protein values (0-40%) in the animals' diet, the optimum and minimum physiological daily doses were determined in 49-day-old growing rats from changes in their body water, body nitrogen and protein intake. The optimum physiological doses were identical with the peak of linearity of the given parameters, which coincided with a 15% casein protein and a 20% gluten protein concentration in the diet. This was also confirmed by the maximum body amino acid values, which were found in animals given a 15% casein or 20% gluten protein diet. It was further confirmed by the finding of significantly elevated alanine aminotransferase and aspartate aminotransferase activity in the liver of animals with a higher intake of the above protein sources. The minimum physiological dose of the given protein was determined from the equations of the regression curves in the presence of zero changes in the body nitrogen or body water content. The optimum physiological daily doses of casein and wheat gluten protein were 3.25 g and 4.05 g respectively. The minimum physiological daily doses of casein protein were 268 mg (from body nitrogen changes) and 371 mg (from body water changes) and the minimum physiological daily doses of gluten protein were 892 mg (from body nitrogen changes) and 1,000 mg (from body water changes). The above indicators demonstrate, in the presence of higher and high dietary concentrations, that an intake of the given proteins over and above the optimum physiological daily dose is at the very least uneconomical (gluten), if not harmful (casein), making this a highly topical problem for further study.

Mounting doses of casein and wheat gluten protein (from 0% to 40% in the diet) were given to adult male rats aged 75-89 days for 14 days. The optimum physiological daily dose, determined from changes in body nitrogen, body water and body weight, was 2.76 g/d for casein protein (corresponding to a 10% casein protein diet) and 3.67 g/d for wheat gluten protein (corresponding to a 15% gluten protein diet). Determined from body weight changes, the daily maintaining dose of casein or wheat gluten protein was 1.054 and 1.511 mg/d respectively, from body nitrogen changes 970 and 1.514 mg/d and from body water changes 1.124 and 1.637 mg/d. Compared with newly weaned animals aged 35-49 days, the optimum physiological daily dietary protein doses for adult animals fall, while the maintaining doses rise.

Using diets with a mounting egg albumin and mutton protein concentration, the authors determined the optimum physiological doses, which are identical with the maximum of linearity of the given parameters, from changes in body nitrogen, body weight and body water. The regression equations of the lines from these parameters were used to determine the minimum physiological doses for newly weaned rats. The optimum and minimum physiological doses of the amino acids in the relevant dietary proteins were also determined by analysing the source for its nitrogen content and other components and for the amino acid spectrum. The optimum dose of egg albumin protein for newly weaned rats was 1.69 g/day (on a 15% protein diet) and of mutton protein 2.56 g/day (on a 12.5% protein diet), with daily amounts of 60 mg methionine, 93 mg phenylalanine, 112 mg valine and 60 mg tyrosine for both proteins. The minimum doses of egg albumin and mutton protein, determined from changes in body nitrogen were 282 mg and 213 mg/day respectively [methionine 10.4 (4.7) mg/day, phenylalanine 16.1 (7.5) mg/day, valine 19.1 (9.2) mg/day and tyrosine 9.8 (5.2) mg/day)].

In a 14-day experiment, adult rats weighting 250-260 g were given ad libitum diets with a constant protein content [casein - 10 %] and a mounting fat content [margarine - 0, 10, 20, 30 and 40 % - added at the expense of carbohydrates]. The growth parameters of protein biological value - PER and NPR - were determined and together with weight increments in correlation to protein an fat intake [a linear correlation] they were used on the basis of their regression equations to calculate the reciprocal relationships of fat and protein intake [for equality y]. By substituting the optimum protein intake [43.3 g/14 days - according to NPU], the optimum fat intake for adult rats was found to correspond to dietary fat concentrations of 9.72 % [y = weight increments], 12,82 % [y = PER] and 11.83 % [y = NPR]. These results wee verified in a biological experiment in which adult animals, for 14 days, were given a limited amount [31 g/animal per day] of diets containing 10 % protein [casein] an d9, 10, 11, 12, and 13 % fat [margarine - at the expense of carbohydrates] with the aim of studying the effect of a mounting fat intake on optimum protein intake [43.4 g/14 days]. The correctness of the mathematical method for determining the optimum fat intake was verified by a biological method [the optimum net protein utilization , NPU, which is highest in diets containing 11 % fats, i.e. 22.5 % of the total energy value of the diet]. It was also found that this method, both along and in conjunction with other methods [especially the one using the NPR parameter], was suitable for the determination of optimum nutrient values.

For 14-day periods, 30-day-old and 90-day-old male rats were fed ad libitum the diets with a constant protein content (casein) of 10 p. c. and with an increased fat content (margarine) of 10, 20. 30, 40 and 50 p.c. (first experiment) and then the diets with a constant protein content (casein) of 10 p. c. and with a constant fat content (margarine) of 30 p. c. (30-day rats) and of 11 p. c. (90-day rats) and with an increasing saccharide content of 31, 36, 41, 46 and 51 p. c. (90-day rats were further fed by 56, 61 and 66 p. c.) composed of rice starch, sugar and potato starch at a ratio of 6.4 : 1.2 :1 (second experiment). Net protein utilization (NPU) was determined on the basis of body nitrogen content and protein intake. The animal liver was examined for the gluconeogenesis by measuring the specific activity of phosphoenolpyruvate carboxykinase (PEPCK). The highest NPU value can be achieved as follows: in 30-day animals by administration of the feeds containing 30 p. c. of fat, 36 p. c. of saccharides; in 90-day animals by 10 p. c. of fat and 51 p. c. of saccharides. Under the optimum nutrition conditions, both age groups utilize protein in the same way. The extreme nutrition conditions are better tolerated by the just weaned animals than by 90-day animals. The results of this biological method were also proved by the course of gluconeogenesis (activated at 40 and 50 p. c. fat content and 31 p. c. saccharide content in the diet fed to 30-day animals; in 90-day animals the activation occurred beginning 20 p. c. fat content and at 31 to 46 p. c. saccharide content). This paper contributes to the determination of optimum physiological nutrient rates by biological and biochemical methods.

For 14 days, SPF male Wistar rats with an initial weight of 60 g were given isocaloric diets (1.7 MJ/100 g diet) containing 10% protein (casein) and 5, 10, 25 and 40% fat (margarine). Two utilization parameters of the protein biological value--net protein utilization (NPU) and liver protein utilization (LPU)--were determined from protein intake and body and liver nitrogen. These results were supplemented by a study of the course of the antithetical processes of gluconeogenesis and glycolysis, of the citric acid cycle and transamination processes and of the liver and muscle amino acid spectrum. A high (40%) fat diet significantly reduced the protein biological value parameters NPU and LPU and liver and muscle amino acid values, stimulated gluconeogenesis and inhibited glycolysis and the citric acid cycle, together with associated transamination processes in the liver. Activation of these processes in the muscles provided substrates for increased gluconeogenesis. The negative effect of a low fat + high carbohydrate diet was less marked. The optimum diet for weaned rats is thus a diet containing 10% protein and 10--25% fat. The study, which submits several possible ways of determining optimum nutrient intakes under different physiological conditions shows that diets with more detailed nutrient concentrations should be used.

Male Wistar rats aged 30, 90, 150 and 360 days were fed ad libitum on diets with an optimum protein and fat content for their respective ages and an increasing saccharide content. Net protein utilization (NPU) was determined from the body nitrogen and protein intake values and the course of gluconeogenesis in the liver was measured by specific phosphoenolpyruvate carboxykinase (PEPCK) activity. According to the growth curve for the standard diet, animals aged 30 and 90 days have a high growth rate (3.245 g/day), 150-day-old rats grow more slowly (1.856 g/day) and 360-day-old animals put on scarcely any weight at all (277 mg/day). In 30-day-old rats, NPU attains maximum values in the presence of a 36% saccharide content in the diet, in 3- and 5-month-old animals in the presence of 51% saccharides and in one-year-old animals in the presence of 41% saccharides in their food. The course of gluconeogenesis also corresponds to these values. PEPCK activity in the youngest age group is greatest in the presence of 31% saccharides in the food, at 90 days it is stimulated in the presence of 31-46% saccharides, at 150 days the decisive concentration is 41 and 46% and at one year proteins are used for saccharide synthesis in diet with a 31 and 36% saccharide concentration. For optimum saccharide values, PEPCK activity is reduced in every age group; together with the maximum NPU values, this indicates that proteins are used for growth and building of the organism at an early age and for the renewal of tissues and organs and maintenance of the organism in adulthood.

Male Wistar rats aged 75 and 150 days were given high fat diet (36.5 weight % and 30 weight % fat) over a period of 14 days. The growth (PER, NPR) and utilization (NPU, LPU) parameters of protein biological value and liver phosphoenolpyruvate carboxykinase (PEPCK) activity were determined. In another experiment, the time dependence of liver gluconeogenesis enzyme (PEPCK and fructose-1,6-diphosphatase /FDP-ase/) and transaminase (alanine and aspartate aminotransferase /ALT, AST/) activities during 24 days' administration of the diet were determined. A 14 days' high fat intake had a negative effect on protein utilization in the organism of 75- and 150-day-old animals, which was more pronounced in the younger age group (a bigger drop in net protein utilization /NPU/ and greater stimulation of PEPCK activity). In 150-day-old animals the negative effect of a high fat intake was already manifested on the 6th to 10th day of the diet to the same degree as in the younger animals on the 14th day, as seen from the increase in all the enzyme activities. The paper presents findings on differences in the degree of the negative effect of a high fat intake on protein utilization with reference to age.

Male rats of the Wistar strain, age 30, 75, 90 and 150 days, were given high-fat feeds (45%, 36.5%, 33% and 30%) ad libitum for 14 days. The net protein ratio (NPR), net protein utilization (NPU), and liver protein utilization (LPU) of the biological value of proteins were determined in comparison with diets considered as optimum for each age category. The specific activity of phosphoenol-pyruvate carboxykinase PEPCK (E.C..4.1.1.32) was measured in the liver of the animals. As demonstrated by the significantly reduced parameters of the biological value of proteins and the activated process of gluconeogenesis, a high intake of fats adversely affected the utilization of proteins in the organisms of 75 to 90 days old animals. The decrease in the NPR and NPU of the weanlings is insignificant; the increase in PEPCK is at the level of significance, which testifies to a good tolerance to the intake of fats by the animals after weaning, with respect to a similar composition of mothers' milk. In the animals with the slower growth and higher protein requirement for the maintenance of the organism (150 days old rats) the reduction of protein utilization and the increase in PEPCK activity as a result of a high fat intake are not so significant as in animals old 75 and 90 days. As suggested by the results, it is necessary to state another length of high-fat administration than 14 days.

In a 14-day experiment, weaned and adult rats were given ad libitum isocaloric diets with a mounting casein content (5, 10, 15, 25 and 40% by weight) and growth parameters of protein biological value, PER and NPR, and the utilization parameters NPU (body protein) and LPU (liver protein) were determined together with phosphoenolpyruvate carboxykinase (gluconeogenetic enzyme) and pyruvate kinase (glycolytic enzyme) activity in the animals' liver. The decrease in all the biological value parameters in weaned rats on 25% and 40% casein diets and in adult rats on 15%, 25% and 40% casein diets shows that these concentrations are too high for the organism. The decrease in PER and diminished weight and body and liver nitrogen increments in both age groups in animals with a low protein intake is evidence that 5% casein is an inadequate concentration. The optimum diet for weaned rats is thus a 15% casein diet and for adult rats a 10% casein diet, as confirmed by the linear correlation between weight increments, body and liver nitrogen and protein intake and also by gluconeogenetic enzyme activity. Under the given experimental conditions the study is a contribution to the determination of optimum physiological doses of proteins.

Male Wistar rats aged 30, 75 and 150 days were fed for 14 days ad libitum on diets with an optimum protein content (15% for 30-day-old, 12.5% for 75-day-old and 10% for 150-day-old animals) and a mounting fat content (from 5 to 40%), supplemented by saccharides (from 76 to 41%). Net protein utilization was determined for each of the diets from the body nitrogen and protein intake values. Protein retention values were determined from protein intake on the basis of net protein utilization (NPU). Energy intake was computed from fat and saccharide intake, using energy coefficients. The optimum fat content of the diet, evaluated from the maximum protein retention value per day and the minimum amount of energy needed for the retention of 1 g protein, is 30% at 30 days, 15% at 75 days and 10% at 150 days. Protein retention per kg body weight falls with advancing age--mildly at 75 days compared with 30 days, but markedly at 150 days. From their smaller weight increments and NPU values and also from their lower protein retention, 150-day-old animals are characterized by slower growth and higher protein requirements for maintenance of their organism likewise demonstrated by the growth parameter net protein ratio (NPR). Energy requirements for total protein retention/day per kg body weight diminish with age. In old age a small amount of energy is needed only for the maintenance of body functions. This study contributes to the expression of the interrelationship of energy requirements and protein retention.

The effect of 14 days' intake of mounting quantities of fats and energy on a constant optimum utilizable amount of dietary protein was studied in weaned rats weighing 60 g. Growth (PER, NPR) and utilization (NPU--body, LPU--liver) parameters of biological protein value were determined, supplemented by a study of the course of the antithetical processes of gluconeogenesis and glycolysis, of the pentose cycle, the citric acid cycle and of transamination processes in the animals' liver. According to the maximum PER, NPR, NPU and LPU values, a 14 days' intake of 59.2 g fats and 4.518 MJ, corresponding to a diet containing 10% protein, 30% fat and 2.274 MJ, had the best effect on the optimum utilizable amount of casein (21 g/14 days). A diet containing 35% and 40% fat stimulated gluconeogenesis, followed by a transamination process and inhibition of glycolysis, the citric acid cycle and lipogenesis (depression of pentose cycle activity and a decrease in the amount of body fat), and simultaneously reduced the values of all four parameters of protein biological value. The results demonstrate that very best diet for newly weaned rats is one containing 10% high quality protein, 30% fat and 2.274 MJ.