Epidermal growth factor-induced mitogen signals in cultured intestinal epithelial cells.

Epidermal growth factor (EGF) stimulated proliferation of an intestinal cell line (IEC-6 cells), derived from rat jejunal crypts. EGF-induced tyrosine phosphorylation was analyzed by immunoblotting with a monoclonal antibody specific for phosphotyrosine. EGF initiated rapid tyrosine phosphorylation of proteins with molecular masses of 185, 170, 55, and 42 kilodalton (kDa). In addition, EGF caused the rapid elevation of intracellular free Ca2+ concentration. Thus, EGF-stimulated proliferation and its mitogen signals were clearly observed in IEC-6 cells, suggesting that EGF may play an important role in the maintenance and repair of the intestinal mucosa in vivo.

Constancy of net protein intake in rats on self-selection regimen with proteins of various qualities.

Voluntary intake of proteins of various qualities in relation to dietary protein utilization was investigated in growing and adult rats. The rats were given two diets, one containing high protein and the other no protein, and were allowed to self-select protein and energy intakes freely from both diets. The results showed that total food intake (protein diet plus protein-free diet) and body weight gain were similar among five proteins tested. However, the amount of protein consumed by the growing rats per 100 g of total food intake (i.e., dietary protein level) was different depending upon the protein qualities, that is, wheat gluten (WG) 44 g, casein (CA) 30 g, soy protein (SP) 21 g, lactalbumin (LA) 19 g, and amino acid mixture simulating egg protein (AA) 11 g. Net protein utilization (NPU), estimated as the proportion of protein intake that is retained in the body, was as follows: WG, 20%; CA, 33%; SP, 44%; LA, 50%; and AA, 74%. From the above figures, net dietary protein value, which is a measure of utilizable protein in the diet, was calculated by multiplying the dietary protein level by NPU. In contrast to the difference in protein intake, net dietary protein value was quite constant in spite of large differences in the dietary protein quality, being 8 to 10%. A similar relationship between protein intake and protein utilization was obtained also with adult rats, except that the net dietary protein value was smaller in adult rats than in growing rats. These results may suggest that the animals can regulate the intake of dietary protein to keep the amount of protein available for the body constant.

Antihypertensive effect of gamma-amino butyric acid enriched soy products in spontaneously hypertensive rats.

The effect of gamma-amino butyric acid (GABA)-enriched soybean on blood pressure was investigated in male spontaneously hypertensive rats. Ten-week-old rats were given diets containing graded levels of GABA-enriched soybean powder for 8 weeks. The systolic blood pressure in rats fed 0.15% GABA diet was significantly lower at 1st week and maintained lower values for 4 weeks as compared with 0% GABA controls. No effect on blood pressure was found in those of 0.03 and 0.3% GABA. The results suggest that there exist appropriate dietary GABA level to get the blood pressure lowering effect.

Effects of protein and energy on dietary selection and protein utilization in rats with ventromedial hypothalamic lesions.

The effect of bilateral destruction of the ventromedial hypothalamus (VMH) on protein and energy intakes was examined in relation to protein utilization. In Experiment 1, rats with VMH lesions were allowed to select protein (either casein or wheat gluten) and energy from two diets containing 70% and 5% protein, respectively. In Experiment 2, they were restricted to 0, 100 and 200 mg N/day of protein and given free access to protein-free diet. In Experiment 3, they were restricted to 2 and 5 g/day of protein-free diet but given 92% protein diet ad libitum. Self-selecting rats with VMH lesions consumed about 100 kcal/day regardless of the protein source, in contrast to sham-operated controls which consumed 75 kcal/day. They showed increased non-protein energy intake with constant protein consumption resulting in normal protein retention with increased body fat. When protein intake was restricted to 200 mg N/day, energy intake was reduced in animals given diet containing wheat gluten more than in those given diet containing casein, resulting in lower protein utilization. Therefore, food intake depended upon the amount of dietary protein. Rats with VMH lesions showed an exaggerated response to the ratio of protein to energy in the diet and consumed more energy from balanced diet but showed more reduction in food intake than controls in response to diet with an inappropriate ratio of protein to energy. The present study confirmed that the VMH was related to regulation of energy intake but not protein intake. It is suggested that protein intake is regulated in relation to maintenance of body protein in rats with VMH lesions as well as in normal rats.

Amino acids and glucose differentially increased extracellular 5-hydroxyindoleacetic acid in the rat brain.

To reveal the role of serotonergic neurons in the regulation of feeding, the levels of 5-hydroxyindoleacetic acid (5-HIAA), a metabolite of serotonin, in the striatum and the hypothalamus were continuously monitored by an in vivo microdialysis technique. Intake of 20% casein diet did not induce significant changes in the 5-HIAA level in these regions. When rats were fed on 5% casein diet (83.5% carbohydrate diet) for 2 h, the level of 5-HIAA in the striatum gradually increased and reached a maximum (226 +/- 44% of basal level, M +/- SEM, n = 7) at 4 h after stopping the diet. In the medial hypothalamus, its level also increased to 183 +/- 19% (n = 10) at 2 h after starting the diet. On the other hand, a 60% casein diet increased the level of 5-HIAA in the lateral hypothalamus to 138 +/- 19% (n = 10) at 2 h after starting the diet. The intravenous infusion of each of these nutrients, glucose, amino acid mixture or lipid, produced more rapid elevation of the 5-HIAA level than oral intake of the diets. When rats were infused with glucose, its level in the striatum continued to be elevated. In the medial hypothalamus, glucose infusion increased 5-HIAA to the maximum (189 +/- 38%, n = 7) at 4 h after starting infusion. In contrast, serotonergic neurons in the lateral hypothalamus seemed to respond only to infusion of the amino acid mixture, and the level of 5-HIAA reached 163 +/- 14% (n = 5) of the basal level at 1 h after starting the infusion. These results suggest that rapid elevation of glucose or amino acids may independently stimulate serotonin metabolism in these brain areas, participating in the feedback regulation of nutrient intake.

Japanese dietary protein allowance is sufficient for moderate physical exercise in young men.

The sufficiency of the dietary protein allowances recommended by the Ministry of Health and Welfare of Japan for various physical exercises has not been examined. We investigated the protein requirement for moderate-intensity physical exercise using nitrogen balance in the isoenergetic state. Seventeen healthy college students exercised for 10 days with an adaptation period of three days and non-exercise control period of 10 days. They were given a maintenance level of energy and 1.08 g/kg per day of high quality mixed proteins recommended by the Ministry of Health and Welfare of Japan throughout the experimental period. They performed treadmill running during the exercise period at about 65% of VO2max for 25, 41 or 48 min/day, which required 200, 300 or 400 kcal of extra energy, respectively. Although the exercise increased dermal nitrogen loss, urinary nitrogen excretion tended to decrease. Consequently, the exercise ranging from 200 to 400 kcal/day did not significantly alter the nitrogen balance. Thiobarbituric acid-reactive substances and glutathione disulfide were not increased after exercise, suggesting that the moderate exercise, recommended for health promotion by the Ministry of Health and Welfare of Japan, does not cause oxidative damage to healthy subjects. These findings demonstrate that a protein intake of 1.08 g/kg per day is enough for moderate exercise.

Optimal protein intake estimated by the resistance to streptococcal infection and the nutritional indices in mice.

Effects of dietary protein levels on the resistance against a bacterial infection and on the nutritional status were studied in mice to obtain basic data for the estimation of an optimal protein intake. Female DDY strain weanling mice were fed 5, 7, 10, 20, 30, or 40% casein diet. At 2 or 4 weeks on the diets, the mice were injected intraperitoneally with 5 x 10(3) or 5 x 10(4) group B streptococci/g body weight and their survival rates were observed for the following 10 days. Nutritional indices and cell numbers of thymus and spleen were also measured. The survival rate was higher in the order of 7, 10, 20, 30, 5, 40% casein diet group. Significant differences were observed between the 7% group and the 30, 5, or 40% group, and between the 10% group and the 5 or 40% group. The nutritional indices and cell numbers of the thymus and spleen were similar among the 20, 30, and 40% casein diet groups and decreased in the order of 10, 7, 5% casein diet groups. From the results, protein levels were categorized into 4 groups: severe protein deficiency with low resistance (5% casein diet), moderate protein deficiency with high resistance (7 and 10% casein diets), normal protein intake with normal resistance (20% casein diet), and high protein intake with low resistance (30 and 40% casein diets). This grouping suggests that when the relation between immunocompetence and nutritional status is considered, both high and low protein intakes are undesirable and the optimal level of dietary protein will be limited to a narrow range.

Comparative effect of intravenously or intragastrically administered glutamine on small intestinal function of the rat.

Effect of glutamine supplementation to parenteral nutrition on small intestinal function was evaluated in malnourished rats as well as normal rats. Animals were administered the solution supplemented with glutamine at 20% of total amino acids either intravenously or intragastrically for seven days. Intragastrically fed rats gained more weight than parenterally fed rats. In malnourished rats, whose small intestinal weight was decreased to 60% by feeding protein-free diet for four weeks or by fasting for seven days, small intestinal weight was further decreased by intravenous infusion but was maintained at the pre-infusion level by intragastric infusion. The intragastric administration of glutamine increased small intestinal weight and mucosal brush border enzyme activities of sucrase, leucine aminopeptidase and alkaline phosphatase, showing the beneficial effect of intragastrically administered glutamine to maintain small intestinal function. In parenteral nutrition, however, it seems that more than 20% supplementation of glutamine relative to total amino acids might be necessary to mitigate intestinal atrophy.

Protein deficiency and excess lipid synergistically augmented lipid peroxidation in growing rats.

The influence of dietary protein and lipid on superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione (GSH) and tissue lipid peroxidation, as measured by thiobarbituric acid-reactive substances (TBARS), was investigated in post-weaning male Wistar rats, fed either a diet containing 5% or 20% corn oil with 5%, 10% or 20% soy protein isolate (SPI) for four weeks. TBARS concentrations in 5% corn oil group was highest in 5% SPI group for all organs, followed by 10 and 20% SPI groups in the liver and 10 and 20% SPI groups in other organs. High lipid diet significantly increased TBARS formation in the liver of 10% SPI group. The liver and kidney SOD and GPx activities were higher in 5% and 10% SPI groups than in 20% SPI group, suggesting an augmented formation of radical substrates for these enzymes in low protein groups. Organ GSH concentrations did not show a linear correlation with dietary protein level. These results suggest that protein deficiency along with high lipid intake accelerates the peroxidative damage of the tissues by increasing oxy-radical formations and/or decreasing the defense mechanism.