Isolated ileal enterocytes incubated with intrinsic factor[57Co]vitamin B12 (IF-B12) at 37°C took up 25 times more B12 than jejunal enterocytes.Uptake of B12 by ileal cells was dependent upon IF and Ca2+. Bit taken up by ileal enterocytes could be separated into two components: 1) B12 which was retained (E component) and 2) released (R-E component) by chelation of divalent cations. The E component could be removed from ileal cells by treatment with Triton X-100. Incubation of ileal enterocytes at 22°C or with 2, 4-dinitrophenol reduced incorporation of B12 into the E, but not the R-E, component. Ileal enterocytes were incubated with IF-[57Co]B12 washed and reincubated with unlabeled IFB12. Reincubation resulted in a decrease in the amount of [57Co]B12 in the R-E component and a concomitant increase of that in the E component indicating that B12 was transferred from the R-E to the E component. Dinitrophenol reduced transfer from R-E to E components. These results suggest that, using isolated enterocytes, two sequential steps in ileal absorption of B12 can be identified: 1) energy-independent binding of IFB12 to its receptor on the brush border followed by 2) an energydependent event which probably represents transfer of B12 from its receptor into the cell.
Effects of α-tocopherol on lipid peroxidation and membrane fluidity were studied in liver microsomes from vitamin E (α-tocopherol)deficient rats using NADPH as a substrate. Microsomes containing various contents of α-tocopherol were prepared by incubation with various concentrations of α-tocopherol in ethanol solution. NADPHdependent lipid peroxidation decreased the content of polyunsaturated fatty acids, arachidonic acid and 4, 7, 10, 13, 16, 19-docosahexaenoic acid. The treatment with α-tocopherol before peroxidation reduced the production of lipid peroxides and the change in fatty acid composition even at the lowest content of α-tocopherol dealt with in this experiment, 0.2 molar fraction, while addition of α-tocopherol after peroxidation resulted in a slight inhibition of peroxide production and small alteration in fatty acid composition. By an ESR measurement using stearate spin probe, the α-tocopherol incorporated into microsomes did not alter the acyl chain mobility up to 0.2 molar fraction but reduced the mobility above 0.2 molar fraction. The acyl chain mobility was markedly decreased by lipid peroxidation. The decrease of membrane fluidity was repressed in microsomes treated with atocopherol before peroxidation, but was not repressed in microsomes treated after peroxidation. The experiment using artificial membranes of egg yolk phosphatidylcholine and rat liver phosphatidylcholine revealed that the effect of atocopherol on membrane fluidity depends on the fatty acid composition of phospholipid, especially the content of arachidonic acid. On the other hand, the mobility of the fatty acyl chain was not affected by spermine at concentrations which could inhibit lipid peroxidation. These results suggest that the inhibitory effect of α-tocopherol on lipid peroxidation is due to antioxidant activity rather than the indirect effect of membrane stabilization.
The effects of thyroxine (T4) and thiouracil (TU) on growth and protein metabolism were examined in male mice given diets containing different levels of protein (casein) at two different growth stages (25 and 60 days old). Changes in protein metabolism were assessed from the expiratory 14CO2 from [U-14C]leucine injected, the liver nucleic acid contents and the rates of synthesis and degradation of liver protein estimated by single injection method using [6-14C]arginine. Each mouse, excluding the control group, received daily intraperitoneal injection of 10μg of L-thyroxine sodium salt per 100 g b.w. (T4 group) or were given a diet containing 0.05% 2-thiouracil (TU group). In the 25-day-old mice, growth of the T4 group was accelerated at protein levels above 15% and that of the TU group was severely retarded at protein levels below 10%. On the other hand, in the 60-day-old mice, growth of the TU group tended to be accelerated at protein levels from 10% to 25%, while it was significantly retarded at the 5%-protein level. The expiratory 14CO2 increased when the growth was retarded, and decreased when growth was accelerated by T4 or TU in both age groups, but was not significant in either case. The nucleic acid content of the liver was increased by both T4 and TU when the dietary protein level was above 15%. The rate of protein synthesis was increased, but not significantly, by T4, while it was not affected by TU. The rate of protein degradation was increased, but not significantly, by TU, while it was not affected by T4 in the 25-day-old mice. In the 60-day-old mice, the rates of both liver-protein synthesis and degradation were significantly increased by TU, while they were not affected by T4. These results definitely indicate that the growth stage and the dietary protein level change the effects of thyroid function on growth and protein metabolism of mice.
Levels of sodium, potassium, calcium, and phosphate were examined in rats fed on an adenine diet. Among the electrolytes in the serum, potassium decreased significantly in the adenine-fed group as compared with the control group. A decrease was observed in the level of serum calcium on feeding with an adenine diet. Though a significant decrease in phosphate was noticed in the adenine-fed rats which were kept for 6 to 12 days, the level of phosphate was increased at the 18-30th day as compared with the control group. However, serum sodium concentration was maintained within a relatively narrow range. On the other hand, the animals that continued on the adenine diet showed a significant rise in the urinary excretion of sodium, potassium, and calcium during the test period. Dietary adenine decreased the amount of urinary phosphate. In addition, 2, 8-dihydroxyadenine content in kidneys increased during the test period, while a significant increase in the urinary excretion of 2, 8dihydroxyadenine was seen until the 12th day of the feeding period. Furthermore, the results of the present study showed that feeding of adenine to rats produced a significant increase in the urine volume. However, there were no appreciable changes in the water intake of the control and adenine-fed groups throughout the experimental period. Key Words dietary adenine, rat, serum, urine, sodium, potassium, calcium, phosphate, 2, 8-dihydroxyadenine, polyuria
Self-selection from carbohydrate, protein and fat sources including essential micronutrients was studied in male Sprague-Dawley rats that were 4 weeks of age at the beginning of the experiment. During the experimental period of 14 days, the intake of carbohydrate and fat was quite constant, whereas that of protein increased gradually. The mean intake of carbohydrate, protein, and fat was 31.1±3.5%, 56.1±4.6%, and 12.8±2.8% of the total energy intake, respectively. Animals fed on a mixed diet consisting of high sucrose, consumed 65.1% of their daily energy as carbohydrate, 17.6% as protein, and 17.3% as fat. Total energy intake and body weight gain were not significantly different between the rats on self-selection and those fed on the mixed diet. These results indicate that young rats on dietary self-selection were able to gain body weight comparable to that of rats fed on the mixed diet. Body energetic status affected self-selection patterns. In rats fasted for 5 days or fed on a protein-free diet for 21 days, fat intake increased, but protein intake decreased. On the other hand, fat intake decreased in animals given a sucrose diet higher in energy content than the stock diet; these animals exhibited increased accumulation of body energy. These results indicate that dietary self-selection is closely related to nutritional and physiological body requirements.
Adult male fatty and lean rats of Zucker strain were given access ad libitum to either a single nutritionally complete diet, or a selfselection regime with separate sources of three macronutrients, protein (casein), fat (hydrogenated coconut oil), and carbohydrate (sucrose). Animals on the single diet were fed on a powdered stock diet, and then switched to the self-selection regime. Energy intake on the self-selection regime was the same as that for the single diet condition in both fatty and lean rats. Fatty rats consumed 45% more energy than did their lean littermates. Further, fatty rats selected 47.0% of their total calories as protein, 30.1% as fat, and 22.9% as carbohydrate. The respective percentages for lean rats were 56.1, 13.0 and 30.9. In lean rats, the injection of insulin (10 U/kg) or 2-deoxy-D-glucose (500 mg/kg, 2DG) failed to increase energy intake, but increased carbohydrate intake 2 times by attenuating protein intake. Also in fatty rats, insulin did not increase energy intake, but it did increase carbohydrate by 50% by attenuating fat intake. 2DG decreased energy intake by attenuating carbohydrate and fat intakes in fatty rats. Fatty rats were slightly less hypoglycemic to insulin, but more hyperglycemic to 2DG than lean rats. These different self-selection patterns of fatty rats seemed to be associated with their endocrine, metabolic, and behavioral abnormalities.
The regulation of phenylalanine intake in rats was investigated by means of a self-selection feeding method. The relationship between phenylalanine intake and the alteration of phenylalanine and tyrosine concentrations in plasma and brain was also studied. Weanling rats were offered a choice of two diets differing only in phenylalanine content for 2 weeks. Weight gain and food consumption of all the selfselecting rats were not significantly different from each other and were of the same levels as those in rats fed on a 10% casein or 10% casein plus 1.0% phenylalanine diet as a fixed ratio. Phenylalanine intake of the selfselecting rats ranged from 0.31 to 2.29% of the food consumed. The phenylalanine and tyrosine concentrations in plasma and brain of selfselecting rats were within normal levels. It became clear that rats have an ability to regulate phenylalanine intake, and that they select phenylalanine to meet their requirement for the amino acid.
The effects of calcium-free and normal (0.6%) and high (1.0%) calcium diets on the transfer of calcium from pregnant mothers to fetuses were investigated by balance experiments. Pregnant rats receiving calcium-free, normal and high calcium diets ate totals of 353, 324 and 280 g of the diet, respectively, during pregnancy, and the food consumption of the latter two groups decreased near term. The group on calcium-free diet was able to maintain pregnancy and produce normal fetuses by using calcium resorbed from the dam's bones. The calcium retentions due to pregnancy in rats on normal and high calcium diets were 116 and 128 mg, respectively, during the first 15 days, and -9 and -109 mg, respectively, during the last 6 days of pregnancy. Fetuses contained about 130 mg of calcium at term and most of this calcium was supplied from the dam's bones, in which extra calcium were retained during early-mid pregnancy. Unexpectedly, the true rate of calcium absorption was appreciably lower during late pregnancy than during early-mid pregnancy in both dietary groups. Thus, extra calcium retention during early-mid pregnancy seemed to be physiological adaptation to a decrease in either food consumption or calcium absorption during late pregnancy. Phosphorus absorption and its balance were examined in relation with the dietary calcium levels.
Male albino rats were fed on respective diets of wheat flour, Bengal gram flour and corn flour for 8 weeks at the 59% level. It was observed that the increase in weight after wheat flour and Bengal gram flour feeding was 6.8 and 12.0% respectively and that the decrease after corn flour feeding was 5.2% as compared to the control animals on sucrose diet. Serum cholesterol and liver cholesterol levels were significantly (p<0.01) decreased after wheat flour, Bengal gram flour and corn flour feeding.