Metabolism of Leucine and Alanine in Growing Rats Fed the Diets with Various Protein to Energy Ratios

In order to clarify the nutritional significance of metabolism of the carbon skeleton of individual amino acids, the metabolic fates of l-leucine-U-¹⁴C and l-alanine-U-¹⁴C were investigated in growing rats fed the diets with various protein calories percents (PC%) at 410 kcal of metabolizable energy.

The incorporation of ¹⁴C into body protein in 12 hr after the injection of leucine-¹⁴C was about 73% of the dose in the 0 and 5 PC% groups, though it decreased with increasing the levels of dietary protein from 10 to 30 PC%. The value of ¹⁴C recovery in body protein almost agreed with the net protein utilization (NPU) determined for the whole egg protein in a similar experimental condition. The ¹⁴C recovery in expired CO₂ and body lipid suggested that the carbon skeleton of leucine is well utilized as an energy source when the dietary carbohydrate is extensively replaced by protein.

While, the incorporation of ¹⁴C into body protein from alanine-¹⁴C was less than about 11% of the dose in all the dietary groups, and the majority of ¹⁴C was recovered in expired CO₂ and body lipid in a remarked contrast to leucine.

A similar pattern in urinary excretion of ¹⁴C was obtained for these amino acids, and the refracted rise of ¹⁴C from 10 PC% may give an indication for minimum protein requirements.     

Metabolism of Histidine in Growing Rats at Various Dietary Protein Levels

The metabolic fate of the carbon skeleton of l-(U-¹⁴C)-histidine has been investigated in growing rats fed diets containing different percentages of protein calories (0, 5, 10, 15 and 30 PC%) at 410 kcal of metabolizable energy per 100 g diet.

The incorporation of ¹⁴C into body protein at 12 hr after injection of ¹⁴C-histidine was about 70% of the dose in rats fed 0 to 10 PC% diets, though the value was reduced in rats fed higher PC% diets. The expired ¹⁴CO₂ production was depressed in the low protein groups, and it showed an inverse pattern to that of ¹⁴C incorporation into body protein. Urinary excretion of ¹⁴C was about 20% of the dose in all dietary groups. The activities of hepatic histidase, urocanase and histidine-pyruvate aminotransferase were increased in the 30 PC% group.

These results indicate that the metabolic response of histidine to dietary protein changes around 10 PC%, where growth rate and body protein retention reached approximate plateaus.

The nutritional significance of the metabolism of histidine has been discussed and compared with that of leucine, alanine and serine reported previously.     

Metabolism of Glycine and Threonine in Growing Rats at Various Dietary Protein Levels

The metabolic fates of the carbon skeletons of [U-¹⁴C]glycine and l-[U-¹⁴C]threonine were investigated in growing rats fed with diets containing different percentages of protein calories (0, 5, 10, 15, and 30PC%) at 4100 kcal of metabolizable energy per kg of diet.

The incorporation of ¹⁴C into the body protein at 12 hr after the injection of ¹⁴C-glycine was about 58% of the dose in rats fed with the 10 or 15 PC% diet, and the values were reduced in both the lower and higher PC% groups. A considerable amount of ¹⁴C was recovered in the soluble fraction, and it was attributed to labeled glycine and serine in the free amino acid pools of the tissues.

The incorporation of ¹⁴C into the body protein from ¹⁴C-threonine was extremely high in the dietary groups of 0 to 10 PC%, and it decreased in the 30PC% group. Conversely, the expired ¹⁴C0₂ production was much less until the dietary protein level reached at 10PC%, and it increased with higher PC% in the diets. The change in the activity of hepatic threonine dehydratase in rats fed diets with increasing protein levels was similar to that of the expired ¹⁴C0₂ production from ¹⁴C- threonine.

These results indicate that, though the metabolic patterns for glycine and threonine differ from each other, their responses to dietary protein levels change at 10 to 15 PC%, where the growth rate reached its approximate maximum.     

Synthesis of Terpene Alcohol Esters by Lipase

The metabolic fates of the carbon skeletons of L-(U-¹⁴C)arginine, proline and glutamic acid were investigated in growing rats fed with diets containing different percentages of protein calories (0, 5, 10, 15 and 30 PC%) at 4100 kcal of metabolizable energy per kg of diet.

The incorporation of ¹⁴C into body protein at 12hr after the injection of ¹⁴C-arginine was more than 50% of the dose in all dietary groups, showing a high efficiency of utilization of this amino acid for protein synthesis. The incorporation of ¹⁴C into body protein from ¹⁴C-proline was most increased in the 15 PC% group, and the values were reduced in rats fed with lower and higher PC% diets. The carbon skeleton of ¹⁴C-glutamic acid was extensively oxidized to expired carbon dioxide, and the ¹⁴C incorporation into body protein was markedly less. The pattern of expired ¹⁴C0₂ production from each ¹⁴C-amino acid was in inverse proportion to that of ¹⁴C incorporation into body protein. The results indicate that the metabolic responses of arginine, proline and glutamic acid to dietary protein change at 10 to 15 PC%, where the growth rate reached its approximate maximum.     

Metabolism of Serine in Growing Rats and Chicks at Various Dietary Protein Levels

The metabolic fate of the carbon skeleton of l-serine-U-¹⁴C has been investigated, in vivo and in vitro, in growing rats and chicks fed the diets with various protein calories percents (PC%) at 410 kcal of metabolizable energy.

The incorporation of ¹⁴C into body protein at 12 hr after the injection of serine-¹⁴C was about 49% of the injected dose in rats fed the 10 or 15 PC % diet, though the value was reduced in rats fed lower and higher protein diets. The ¹⁴CO₂ production was smaller in rats fed the 10 and 15 PC% diet, and it showed an inverse pattern to that of the ¹⁴C incorporation into body protein. Urinary excretion of ¹⁴C was higher in rats fed 10 and higher PC% diets, whose growth rate and net body protein retention were maximum.

In contrast to the case of rats, the incorporation of ¹⁴C into body protein of chicks at 6 hr after the injection was rather reduced in the 15 PC% group. The proportion of ¹⁴C excreted as uric acid was remarkably increased above the 10 PC% group, and about 19% of the injected dose was recovered in the 50 PC% group.

The catabolic rate of serine in the liver slices of rats and chicks was increased by high protein diets.

These results support the concept that the nutritional significance of metabolism of the carbon skeleton of serine in growing rats and chicks is different from each other, especially at high protein diets.     

Growth-promoting Activity of an Aqueous Extract of Soybean Seeds for Some Microorganisms

The metabolic fates of the carbon skeletons of leucine, lysine, and threonine were studied in growing rats on the diets containing graded levels of protein calorie percentages (10, 20, 30, and 40PC%) by use of either gluten or zein at 4100 kcal of metabolizable energy per kg of diets. In growth experiment for 21 days, body weight gain, food intake, and body fat increased at higher PC% in the gluten diets, but rats given zein did not maintain their initial weight even at 40PC%. The concentration of plasma free lysine remained low with the zein diets, but plasma threonine increased at 10 and 20PC% in the gluten and zein diets, respectively. Plasma leucine increased as the protein level increased either dietary protein. More than 70% of ¹⁴C was incorporated into body protein 12 h after an intraperitoneal injection of labeled lysine in all groups, but little ¹⁴CO₂ was expired in rats on the gluten and zein diets. About 79% of ¹⁴C-threonine was incorporated into body protein in rats given the gluten and zein diets at 10PC%, but the values were gradually decreased with increasing the dietary protein levels. Some 40–50% of ¹⁴C-leucine was incorporated into the body protein in rats given the gluten diets, and the values for the zein diets were extensively decreased in the higher PC% groups where the expired ¹⁴CO₂ was inversely increased to a great extent. These results showed that, when a specific amino acid was limiting or deficient in the diet, the major portion of the labeled amino acid was utilized for body protein synthesis and little was oxidized to carbon dioxide, whereas the oxidative degradation of essential amino acid other than limiting one was increased and the efficiency of the amino acid utilization was relatively decreased.     

Effect of Dietary Protein and Energy Levels on the Growth Rate,Feed Efficiency and Carcass Composition of Chicks

Feeding day-old White Leghorn male chicks 9 different diets for 4 weeks with the orthogonal composite design, we studied the relationship among dietary protein, energy levels and chick’s responses.

The ellipsoid relationship has been found fitted to describe the relationship between dietary composition and weight gain or feed efficiency of chicks, whereas declined planes are fitted to show the relationship between dietary composition and carcass protein or fat levels of chicks. Dietary protein level has great influence on nitrogen retention, but dietary energy level has little effect.

The linear relationship between total digestible nutrients and metabolizable energy in diets is presented.     

Lower fat deposition and energy utilization of growing rats fed diets containing sorbose

1. Growing rats were fed diets containing graded levels (0, 100, 200 and 300 g/kg diet) of sorbose for 6 weeks. Protein, fat and energy deposition were determined by carcass analysis. 2. The values for growth, serum insulin level, digestible energy (DE), metabolizable energy (ME) and fat and energy deposition declined with the increment of dietary sorbose. 3. The efficiency of protein utilization (protein retained/protein consumed) was hardly affected by dietary sorbose. The DE and ME of sorbose per se was calculated as 14.09 and 12.35 kJ/g respectively. The efficiency of energy utilization (energy retained/ME intake) decreased with the increase of dietary sorbose, although sorbose had an ME. 4. The relative weights of gastro-intestinal tract and liver were positively associated with dietary sorbose level, although the reverse was true for the amount of stomach content, being heavier with higher dietary sorbose. 5. It is suggested that dietary sorbose, as a sweetener as well as a bulky agent, seems to be a suitable sugar for the obese and diabetic with special reference to lower body fat and energy deposition without reducing protein utilization.     

The effect of lysine intake on energy partitioning and utilization in growing pigs

An experiment utilizing 12 castrated male pigs within a body weight range of 23 - 147 kg was conducted to ascertain whether the alteration of protein quality by varying the level of lysine intake is influencing total energy retention, heat production and therewith efficiency of energy utilization for growth. The animals were allotted to two treatments of a constant medium (11.5 g/d) or high lysine intake (13.5 g/d) level on the basis of an isonitrogenous diet at an energy intake level of 1.3 MJ ME/kg BW0.75. Representing a tool for determining body composition, at target body weights of 35, 55, 80, 115 and 145 kg measurements of deuterium dilution space were undertaken. Protein and lipid accretion were calculated by difference, assuming accretion to contain 23.8 and 39.0 kJ/g, respectively. The results show a significant effect (p < 0.05) between treatment groups for the values of energy retained in protein, thus ensuring the intended alteration by protein quality. Furthermore total energy retention, heat production (difference between ME intake and energy retention) and therewith energy utilization demonstrate independence from the composition of body weight (BW) gain. These observations confirm earlier results, but however, seem to be in contrast to the supposition of a constant efficiency for protein (kp) and fat (kf) accretion, respectively. This may be attributed to a variable kp, in fact to a smaller kp at minor values for protein accretion due to an increased whole body protein turnover. Lacking evidence from experimental data for advantages in using constant values for kp and kf to determine the accurate energy requirement for growth, a uniform value for the efficiency of total energy retention seems to be more adequate.     

高山姬鼠冷驯化过程中的能量收支

为探讨栖息于横断山地区高山姬鼠的能量代谢特征,采用食物平衡法,在冷驯化条件下,对其能量收支进行了测定。分别测定了冷驯化(5 ± 1℃ ,42 d)过程中,高山姬鼠体重、体温、每日摄入能、消化能、消化率、粪便能及可代谢能、可代谢率的变化。结果表明:随着冷驯化时间的延长,高山姬鼠的体重和体温降低,28 d 时达到最低值后保持稳定,其中体重在冷驯化14 d 时即与对照组有显著差异,28 d 时平均比对照组降低了15.5% ,体温在14 d 后和对照组有显著差异。每日摄入能、消化能、可代谢能升高,三者均在冷驯化14 d 后与对照组有极显著差异,21 d 时达到最高后保持稳定。粪便能、消化率和可代谢率在冷驯化过程中没有显著变化。高山姬鼠在冷暴露过程中,通过降低体重减少绝对能量需求;通过降低体温减少用于维持体温恒定所消耗的能量;通过增加能量摄入维持正常的生理机能。高山姬鼠在冷驯化过程中表现出的变化模式,与其低纬度、高海拔、年平均温度较低的生存环境有关,这在一定程度上反映了横断山区小型哺乳动物在低温胁迫下的生存机制和适应对策。     

Triglyceride Release and Fatty Acid Oxidation by the Perfused Liver of Rats Fed a Low Protein Diet

Livers of growing rats fed a 5 or 20 protein calories percent (PC %) diet containing purified whole egg protein for three weeks were perfused in situ and the release of triglycerides (TG) and the oxidation of fatty acid by the liver alone were estimated by infusing palmitic acid-l-¹⁴C to the perfusion medium.

The release of TG from the liver of the 5 PC% group was significantly lower in both unfractionated perfusate plasma and perfusate plasma very low density lipoprotein (VLDL) than that of the 20 PC% group, whereas the content of liver TG of the 5 PC% group was higher than that of the 20 PC% group. Significantly lower radioactivity appeared in TG of both unfractionated perfusate plasma and perfusate plasma VLDL of the 5 PC% group than that of the 20 PC% group, while total radioactivity of liver TG was higher in the 5 PC% group than in the 20 PC% group. The ¹⁴CO₂ production in the perfused liver of the 5 PC% group increased gradually with time rather than decreased in comparison with that of the 20 PC% group.

These findings suggest that a major factor responsible for the liver lipid accumulation in rats fed the low protein diet is not an impaired fatty acid oxidation in the liver but an impaired secretion of TG from the liver.     

15N-Harnstoffumsatz bei Schafen nach Verabreichung in gelöster Form

Two slaughter experiments were carried out to determine whether the protein content of the diet has an influence upon the efficiency of utilization of ME in fast growing chickens. A normal‐protein diet (NPD, 204 g CP/kg DM; 14.7 MJ ME/kg DM) based on soybean meal as the sole source of protein was given at four different levels of intake (ad libitum or restricted at about 90, 65 and 40% ad lib) to 10‐d‐old animals for 2 weeks. In a parallel experiment the chickens were fed ad libitum a low protein diet (LPD, 66 g CP/kg DM; 15.0 MJ ME/kg DM) based on soybean meal. The intake of metabolizable energy ranged from 1675 to 777 and 1770 to 832 kJ/kgW^0.75 per day for NPD and LPD treatments, respectively. Mean values of energy retention, gross efficiency of energy utilization and energy retained as protein were significantly (P<. 05) lower and heat production (expressed as both kJ/kgW^0.75 per day and kJ/kg body protein content^0.75 per day) was significantly higher (P < .05) for the chickens fed on LPD. These findings support the concept of dietary‐induced thermogenesis in response to reductions in dietary protein concentration. It is concluded that the increased heat production found in the birds fed on the low‐protein diet can be explained by both an increase in energy requirements for maintenance (ME_m) and a sharp decrease in the efficiency of utilization of ME for growth (k₈).     

The influence of sulphur,molybdenum and cadmium exposure on the growth of goat,cattle and pig

A three factorial designed feeding experiment with common carp (Cyprinus carpio L.) was carried out in an intensive experimental rearing system. Fish (initial body weight 200 g) were fed on two different levels of dietary energy (16 and 18 MJ DE/kg DM), two different levels of protein (320 and 420 g CP/kg DM) and also two different feeding intensities (100% and 75% of the maximum intake). The experiment was terminated when fish reached a mean body weight of 1300 g.

Growth, feed utilization and nutrient composition of the whole body and fillet were observed. The highest growth was obtained when the fish were fed on the diet containing high dietary energy and high dietary protein with satiation feeding. High dietary energy, high dietary protein and restriction of feed intake improved feed conversion ratios. High dietary energy, low dietary protein and restrictive feeding increased energy utilization. Low dietary protein and restrictive feeding resulted in better protein utilization.

Fish fed with high dietary energy contained more fat and less protein in their carcasses. A lower fat content but higher protein and higher ash content in fish carcasses was shown when fish were fed with a diet high in protein and fed restrictively.     

Energy/protein ratio in natural-ingredient diets for weanling rats. II. Energy and protein retention and efficiency of retention

A 3 x 3 factorial experiment was carried out, in which natural ingredient diets formulated at 3 digestible energy levels (DE) (100, 90 and 80% of NRC, 1978 recommendations) and at 3 energy: protein ratios (EPR) (63, 71 and 79 kJ DE/g crude protein (CP)) were fed to 8 weanling male Wistar rats/group. Half of these animals were sacrificed at the end of the 6-week experimental period and their body composition analyzed. Retentions of protein and energy were assessed by difference from a similar group of 8 rats killed and analyzed at the beginning of the experiment. No interaction was found between the 2 factors studied. Main results showed a decrease in intake and retention of both energy and protein, without affecting the efficiency of retention when energy level of diets was reduced by 20%. An increase in the EPR of the diets led to a decrease in protein intake and to an increase in efficiency of protein retention, without affecting the amount retained. No changes in body composition, nor in composition of live weight gains were found as a result of treatments. It is concluded that a 10% reduction in DE level of the diet is of no consequence, and that an EPR of 79 kJ/g leads to more efficient use of the dietary protein without detrimental effects over any other nutritional indicator.     

异育银鲫幼鱼对饲料苯丙氨酸需求的研究

通过55d的生长实验确定异育银鲫幼鱼对饲料苯丙氨酸的适宜需求。实验结果表明,饲料苯丙氨酸含量为1.09%时,异育银鲫幼鱼的增重率、特定生长率和饲料效率均到达最大值,分别为194.50%、1.96%/d、37.74%,而摄食率为最小值4.76%/d。饲料添加适宜水平的苯丙氨酸也显著提高其蛋白质效率、蛋白质沉积率和能量沉积率,均以1.09%处理组显著高于其他各处理组(P0.05)。根据异育银鲫幼鱼特定生长率与饲料苯丙氨酸水平的剂量效应关系,通过非线性回归可以得出饲料酪氨酸为1.04%时异育银鲫幼鱼的苯丙氨酸最适需求量占饲料1.09%,占饲料蛋白的3.02%。       

Protein requirement of the prawn Marsupenaeus japonicus estimated by a factorial method

The protein requirement to give maximum body protein retention in the prawn Marsupenaeus japonicus was assessed by determining both daily protein needed for maintenance (M) and daily body protein increment (G) when the juvenile prawn was maintained on a diet containing high quality protein. The body protein increment was obtained by determining carcass nitrogen increment when the prawn was fed on casein-based diets. The protein required for maintenance was estimated by regressing weight gains of the prawn on the diets containing graded levels of casein. True daily increase or retention of body protein in the prawn corresponded to the sum of G and M, and it was 3.2 g protein per kg body weight per day. The dietary protein requirement of juvenile M. japonicus for maximum body protein retention was suggested to be about 10 g per kg body weight per day providing that the prawn was fed the casein-based diet containing 50% crude protein (net protein utilization = 32) at the feeding level of 2%.     

不同蛋白质和脂肪水平对1龄团头鲂生长性能和体组成的影响

试验采用3×3因子设计,探讨了饲料中不同蛋白质和脂肪水平对1龄团头鲂[均重:(50.37±1.27)g]生长性能和体组成的影响。试验设3个蛋白质水平(25%、30%和35%)和3个脂肪水平(3%、6%和9%),共配制9组饲料。试验鱼饲养于网箱(规格为2 m×1 m×1 m)中,每天投喂3次,试验期为8周。结果表明:蛋白质和脂肪之间无交互作用存在(P>0.05)。蛋白质和脂肪水平对存活率无显著影响(P>0.05)。增重率、特定生长率和饵料系数显著受蛋白质和脂肪水平影响(P<0.05)。其中,25%蛋白组的增重率及特定生长率显著低于其他蛋白组(P<0.05),而6%脂肪组显著高于其他脂肪组(P<0.01)。尽管35%蛋白6%脂肪组的饵料系数最低,但与除了25%蛋白3%脂肪和25%蛋白9%脂肪这两组外的其他组相比,差异均不显著(P>0.05)。蛋白效率比和氮保留率随蛋白质水平的升高显著降低(P<0.05)。此外,蛋白效率比显著受脂肪水平的影响(P<0.05),以6%组最高。能量保留率随脂肪水平的升高显著升高(P<0.05)。鱼体肥满度随蛋白质和脂肪水平的升高显著升高(P<0.05)。腹脂率和肝体比随脂肪水平的升高显著升高(P<0.05),而受蛋白质水平的影响较小(P>0.05)。蛋白质水平对全鱼、胴体和肝脏的组成均无显著影响(P>0.05)。脂肪水平对全鱼水分、脂肪和能量有极显著影响(P<0.01),其中,全鱼水分含量随脂肪水平的升高显著降低(P<0.01),而脂肪和能量含量则显著升高(P<0.01)。胴体和肝脏水分、脂肪含量的变化趋势与全鱼基本一致。以上结果表明,1龄团头鲂的适宜蛋白质和脂肪水平分别为30%和6%,适宜蛋能比为18.21 g/MJ。     

The responses of rats to various combinations of energy and protein. II. Diets made from natural ingredients

Natural diets with metabolizable energy levels of 8.5, 10.0, 11.5 or 13.0 MJ/kg and protein:energy ratios of 1:1, 1.33:1, 1.67:1 or 2:1 %:MJ/kg were fed ad libitum for 28 days to male and female weanling rats. Records of food intake and bodyweight were maintained weekly, and at post mortem examination body length, abdominal fat, liver and kidney weights were measured. Food intake was reduced when dietary energy level increased but this reduction was not sufficient to prevent energy intake increasing, especially in males. Female rats showed only small increases in energy intakes as dietary energy levels rose. The increase in energy intake at higher dietary energy levels increased food conversion efficiency, weight gain and abdominal fat deposition. The responses of male rats were greater than females. Protein intake had a smaller and less consistent effect than energy intake. Increased protein:energy ratio resulted in higher absolute and relative liver and kidney weights and greater body length. This reflected the increase of bodyweight gain at higher protein:energy ratios.     

The responses of rats to various combinations of energy and protein. I. Diets made from purified ingredients

Male and female weanling rats were fed ad libitum for 28 days on purified diets with metabolizable energy levels of 8.0, 9.5, 11.0 or 12.5 MJ/kg and protein:energy ratios of 1:1, 1.33:1, 1.67:1 or 2:1 %:MJ/kg at each energy level. Major nutrients were balanced in proportion to energy and protein. The following parameters were measured: food intake, bodyweight, body length, abdominal fat, liver and kidney weights. Increasing dietary energy level reduced food intake but the reduction was not sufficient to prevent an increase in energy intake. This was reflected by increases in bodyweight, body length, abdominal fat, and relative liver and kidney weights, especially in male rats. Higher energy intake increased weight gain and food conversion efficiency to a greater extent than higher protein intake. The response to protein intake at different energy levels was not consistent. There was no common protein:energy ratio for overall good performance. It is concluded that rat growth and other features can be controlled by the alteration of dietary energy and protein levels.     

饲料中不同蛋白、脂肪水平对春鲤生长、饲料利用和体成分的影响

研究旨在探讨洱海土著鱼类春鲤(Cyprinus longipectoralis)(初始体重0.55 g)对蛋白质和脂肪的需求量。实验采用3×3双因子设计,蛋白水平为33%、39%和45%,脂肪水平为5%、8%和11%,共9组等能饲料。实验在水温为(28±2)℃的室内微流水系统中进行,为期56d。实验结果表明:随着蛋白水平的提高,摄食率显著降低(P<0.05),饲料效率、能量沉积率、鱼体水分和脂肪含量显著升高(P<0.05),但特定生长率、蛋白质效率、蛋白沉积率、鱼体灰分含量和能值均无显著变化(P>0.05)。随着脂肪水平的提高,特定生长率、蛋白沉积率和鱼体蛋白含量显著下降,鱼体脂肪含量显著上升(P<0.05),而摄食率、饲料效率、能量沉积率、鱼体水分和灰分含量以及能值则无明显变化(P>0.05)。通过折线回归分析得出,当饲料中蛋脂比为7.30时,春鲤有最大的特定生长率。研究结果表明,春鲤饲料中适宜的蛋白和脂肪水平分别为33%—34%和4%—5%。