Effect of diets supplemented with amino acids on intestinal sucrase and leucine aminopeptidase activities in rats.

In order to investigate the relationship between dietary amino acids and protein, and activities of intestinal sucrase [EC 3.2.1.26] and leucine aminopeptidase [EC 3.4.11.1, LAPase] in rats, the effect of supplementation of amino acids into a protein-free diet and a low casein diet containing sucrose as the carbohydrate source on these enzyme activities was studied. The segmental weights of the small intestine and its mucosa of rats fed the protein-free diet supplemented with L-methionine or with L-methionine and L-threonine at 0.1 or 0.2% levels were significantly higher than those of rats fed the protein-free diet or one supplemented with L-glutamic acid, but there was no difference in the segmental activities of the sucrase and LAPase among rats fed these diets. On the other hand, the supplementation of methionine or methionine plus threonine to the 5% or 10% casein diet produced remarkable increases in the segmental weights of the small intestine and its mucosa as well as in the segmental activities of the sucrase and LAPase. There was no difference between the segmental sucrase activity of rats fed the 10% casein diet supplemented with 0.2% methionine ad libitum and that of rats fed this diet under restricted feeding conditions, although the segmental LAPase activity was affected by the amount of food consumed.     

Effects of amino acid imbalance and protein content of diets on food intake and preference of young, adult, and diabetic rats.

Effects of histidine or methionine imbalance and dietary levels (3-50%) of casein on food intake and preference of young, adult, and diabetic (2.5 month old) rats were examined. Depressions in food intake and growth caused by ingestion of the imbalanced diet were greatest in young rats and least or absent in diabetic rats. Alloxan diabetes induced hyperphagia and elevated concentrations of plasma branched-chain amino acids and decreased concentrations of tryptophan and tyrosine. The diabetic rats fed the imbalanced diet for 9 days had a higher concentration of the limiting amino acid in the plasma than the adult normal rats fed the same diet. The diabetic rats preferred the imbalanced diet over a protein-free diet when they were fed these diets concurrently. Ingestion of the imbalanced diet by normal rats caused greater changes in plasma and brain amino acid patterns than did the protein-free diet. Unlike the diabetic rats, the normal rats, especially the young rats, strongly preferred the protein-free diet over the imbalanced diet. The normal rats also preferred a 10% casein diet supplemented with L-methionine over a low or high casein diet. It seemed that young rats were able to select a protein diet that supported maximal growth when proportions of dietary amino acids were balanced. It also seemed that the susceptibility of the rats to amino acid imbalance varied directly with the status of overall protein synthesis of the animals.     

Threonine imbalance, deficiency and neurologic dysfunction in the kitten

The effect of feeding threonine-imbalanced and threonine-deficient purified diets (containing L-amino acids as the only source of dietary nitrogen on food intake, weight gain and blood plasma amino acid pattern has been examined in growing kittens. The imbalance was created by adding 17.5% of amino acid mixture lacking threonine to a low amino acid basal diet comtaining 17.5% amino acid mixture including 0.4% threonine. A depression in food intake and weight gain occurred while feeding the imbalanced diet which was corrected by adding an additional 0.2% threonine to the imbalanced diet. There was no adaptation with time in the form of increased food intake or weight gain while feeding the imbalanced diet. Plasma threonine was consistently and similarly depressed (10 to 35% of normal) while feeding the basal, imbalanced and corrected diets and increased to normal when the standard diet with 1.4% threonine was fed. Plasma threonine and total amino acid concentrations of kittens fed the imbalanced diet did not differ from those observed in kittens fed the basal diet. Signs of neurologic dysfunction and/or lameness developed in 14 of the 17 kittens fed threonine-imbalanced or deficient diets, which resolved as dietary threonine was increased.     

The effect of valine deficiency on neutral amino acid patterns in plasma and brain of the rat

Valine deficiency in rats produced motor incoordination attributable to selective damage to the red nuclei, midbrain structures that modulate motor activity. Neither incoordination nor red nuclei damage occurs in rats deprived of valine, isoleucine and leucine, thus suggesting that valine neurotoxicity results from amino acid imbalance rather than from lack of valine per se. To explore this possibility, we compared neutral amino acid patterns in plasma and brain of rats fed for 7 days a complete diet fed ad libitum or pair-fed, a valine-free diet or a diet lacking in all three essential branched-chain amino acids (BCAA). Statistical evaluation showed that plasma valine in valine-deprived rats was lower (P less than 0.01) than in pair-fed and ad libitum-fed controls but did not differ from rats lacking BCAA. Brain valine in valine-deprived rats did not differ from ad libitum-fed controls and actually was higher (P less than 0.01) than in pair-fed and BCAA-deprived rats. The most striking changes seen in the amino acid pattern of valine-deprived rats as compared to all other groups were in the increased leucine:valine ratio (P less than 0.01 for plasma and brain) and in the increased leucine + isoleucine:valine ratio (P less than 0.01 plasma; P less than 0.001, brain). These results are consistent with the view that amino acid imbalance is a critical factor in the development of the neurotoxicity of valine deficiency.     

Histidine-imbalanced diets stimulate hepatic histidase gene expression in rats.

A high protein concentration in the diet induces the gene expression of several amino acid degrading enzymes such as histidase (Hal) in rats. It is important to understand whether the amino acid pattern of the dietary protein affects the gene expression of these enzymes. The purpose of the present work was to study the effect of a histidine-imbalanced diet on the activity and mRNA concentration of rat hepatic histidase. Seven groups of six rats were fed one of the following diets: 1) 6% casein (basal), 2) 20% casein, 3) 35% casein, 4) an imbalance diet containing 6% casein plus a mixture of indispensable amino acids (IAA) equivalent to a 20% casein diet without histidine (I-20), 5) 6% casein plus a mixture of IAA equivalent to a 35% casein diet without histidine (I-35), 6) a corrected diet containing 6% casein plus IAA including histidine equivalent to a 20% casein diet, 7) a corrected diet containing 6% casein plus IAA including histidine equivalent to a 35% casein diet. Serum histidine concentration was inversely proportional to the protein content of the diet, and it was significantly higher in rats fed the corrected diets compared to their respective imbalanced diet groups. Hal activity increased as the protein content of the diet increased. Greater histidine imbalance resulted in lower food intake and higher Hal activity. Rats fed histidine-corrected diets had lower activity than their respective imbalanced groups. Differences in Hal activity were associated with differences in the concentration of Hal mRNA. These results indicate that rats fed a histidine-imbalanced diet exhibit reduced food intake and weight gain and increased Hal gene expression as a consequence of an increased amino acid catabolism.     

Influence of selected amino acid deficiencies on somatomedin, growth and glycosaminoglycan metabolism in weanling rats

The effects of lysine-, methionine- or histidine-deficient diets compared to a control diet fed ad libitum or 15, 10 or 5 g/d were studied in weanling rats. Feed intake was 5-7 g/d for the amino acid-deficient animals. After 3 wk, all amino acid-deficient rats had lost more weight (P less than 0.01) than the controls fed at comparable energy levels. Serum somatomedin (Sm) activity was significantly decreased in lysine- (0.55 U/ml), methionine- (0.32 U/ml) and histidine-deficient (0.38 U/ml) rats compared to rats fed the control diet ad libitum (1.6 U/ml). Differences between amino acid-deficient and calorie-restricted animals were not significant. A similar response was observed in 35SO4 uptake by cartilage glycosaminoglycans (GAG). Caloric restriction and amino acid deficiency each resulted in lower 35SO4 uptake by cartilage GAG than occurred with ad libitum feeding, but there were no significant differences between the rats fed amino acid-deficient diets and those fed 5 or 10 g of the control diet. Compared to rats fed the control diet ad libitum, plasma growth hormone (GH) concentrations were lower in the rats fed 5 or 10 g of control diet per day and in those fed amino acid-deficient diets (P less than 0.05), but GH concentrations were not consistent with the growth retardation observed. The results confirm that Sm and GAG activities are reduced in protein-energy restriction independent of GH. However, changes could not be attributed to specific deficiencies of lysine, methionine and/or histidine.     

Effect of level of dietary protein and total or partial starvation on catalase and superoxide dismutase activity in cardiac and skeletal muscles in young rats

In cells the level of potentially toxic superoxide radical (O2-) is controlled by superoxide dismutase (SOD); the level of hydrogen peroxide (H2O2), also potentially toxic, is controlled by catalase and glutathione peroxidase. To study the effects of altered food intake or dietary protein content on SOD and catalase in cardiac and skeletal muscles, young rats were fed ad libitum diets containing 3, 6 or 25% casein or were subjected to total or partial food restriction (resulting in similar body weight losses). Rats fed a diet containing 3 or 6% casein had much lower growth rates than those fed 25% casein, but the muscle catalase activities were similar in all three groups. Catalase activities in muscles of rats whose food intake was restricted were twice those in rats fed ad libitum. Rats fed ad libitum had higher muscle SOD activities at 41 days of age than did 25-day-old rats, irrespective of the amount of dietary protein or the rate of growth. Twenty-five-day-old rats whose food intake was totally restricted for 2 days had skeletal muscle SOD activities similar to the higher activities seen at 41 days of age in ad libitum-fed rats, but SOD activity in the heart was unchanged after food restriction. The responses of catalase and SOD in muscles differ from the responses reported for these enzymes in liver and erythrocytes when food intake or dietary protein is altered.     

Effect of dietary protein and food restriction on milk production and composition, maternal tissues and enzymes in lactating rats

Lactating rats have been fed either a protein-restricted diet (10 vs. 20% casein in the control diet) or the control diet at 80, 60 and 40% of the voluntary intake for 7 d from d 7 of lactation. Food consumption, changes in maternal live weight, litter live weight gain and the mass of several maternal tissues were determined together with the activity of several mammary and liver enzymes, including 10 that are essential for fatty acid and complex lipid synthesis. Milk production was estimated from the litter weight gain and litter weight. Lactating rats fed the 20% protein diet ad libitum consumed three times that of nonlactating rats; their liver and kidney masses were significantly higher and their adipose mass was lower. The livers of the lactating rats were fatty, containing 118 mg lipid/g compared with 42 mg/g for the nonlactating rats. Lactating rats fed either the protein-restricted diet or the control diet at 40 and 60% of the ad libitum intake of the control diet had lower mammary, liver and kidney masses than rats consuming the control diet ad libitum. Both protein and food restriction led to lower rates of milk production than those of ad libitum-fed control rats as evidenced by the decrease in litter live weight gains. The concentrations of total lipid, total protein and lactose in milk were not affected by these dietary treatments. The concentration of alpha-lactalbumin in milk of rats fed the low protein diet was, however, lower than that in the milk of all rats receiving the control diet, irrespective of intake. Consumption of the restricted diets resulted in only small changes in specific activities (mu/mg protein) of 15 mammary enzymes. In the livers, lactation led to higher specific activities of all four soluble lipogenic enzymes examined but did not affect the particulate enzymes involved in complex lipid synthesis. The dietary restrictions resulted in lower specific activities of the soluble enzymes compared with those of the lactating rats consuming the control diet ad libitum without affecting the particulate enzymes. Total activities of these enzymes were, however, lower than those for the control rats as a result of the smaller liver mass in the rats receiving the restricted diets.     

Yeast proteins enhance satiety in rats

This study was designed to characterize the suppressant effect of yeast protein and purified peptides on energy intake. For this purpose, 5 experiments were carried out using adult male Wistar rats. Rats that consumed ad libitum a standard yeast protein diet ate significantly less and were leaner over 21 d than rats that consumed ad libitum a standard milk protein diet (Expt. 1). Moreover, rats fed a high yeast protein load reduced their next meal and daily energy intake more than rats fed any other well-balanced, amino acid, high protein load (soy, total milk protein, or wheat gluten) and more than those fed a wheat starch diet (Expt. 2). Purified peptides from the yeast protein extract produced similar effects on subsequent energy intake (Expt. 3). Study of the behavioral satiety sequence showed that rats consuming P14-y or P55-y diets ad libitum did not acquire a conditioned food aversion (Expt. 4). Finally, a preliminary study of gastric emptying in rats fed yeast protein loads showed that yeast protein was emptied more rapidly through the pylorus than total milk protein during a meal, which may induce satiety (Expt. 5). Taken together, these experiments show that yeast proteins enhance satiety in rats more than other proteins.     

Studies on the severity of various amino acid imbalances in the young male rat.

Relative severities of amino acid imbalance were compared in young male rats fed diets having an amino acid imbalance with respect to various essential amino acids. In the imbalanced diets, one or more essential amino acids were made to be low, ranging from suboptimal to two times the requirement, while the other essential amino acids were present at three times the requirement. From the extent of depressions in food intake and growth, the severity of amino acid imbalance was found to be dependent upon the level as well as the type of the limiting amino acid(s) in each imbalanced diet. The overall results indicated that Met imbalance was very severe, followed in decreasing order by Ile, Trp, Leu and Val, His, Phe, Thr, Lys and Arg imbalance. The imbalance with respect to the large neutral amino acid appeared to be more severe than the imbalance with respect to the small neutral amino acid, while the imbalance with respect to the basic amino acid was least severe.     

Threonine metabolism of chicks fed threonine-imbalanced diets

Experiments were conducted to determine the metabolic fate of threonine in chicks fed threonine-imbalanced diets. Threonine imbalance was produced by the addition of 3% serine to a threonine-limited diet, and prevented by the addition of 0.2% threonine to the diet. Serine decreased plasma and liver free threonine concentrations, and increased hepatic threonine dehydrogenase and threonine aldolase activities. All changes, including reduced food intake, appeared to occur within 1 day of feeding the imbalanced diet. Despite the decrease in free threonine concentrations and the increase in threonine aldolase and threonine dehydrogenase activities, net threonine catabolism was not markedly increased. This was evidenced by similar amounts of 14CO2 exhaled by chicks fed control and imbalanced diets containing L-[U-14C] threonine, and by similar growth of chicks that were forced-fed both diets to maintain equivalent food intake. It is possible that increases in threonine catabolism contribute to depressions of plasma and tissue threonine concentrations. However, the growth depression caused by serine-induced threonine imbalance is due to depressed food intake.     

Adaptation of rats to diets containing different levels of protein: effects on food intake, plasma and brain amino acid concentrations and brain neurotransmitter metabolism

Food intake, plasma and brain amino acid concentrations, liver amino acid catabolic enzyme activities, and whole-brain neurotransmitter and metabolite concentrations were measured in young rats adapted for 11 d to diets containing from 5 to 75% (in increments of 5%) casein. Food intake was depressed initially in rats fed diets containing 5, 10% or greater than 35% casein. For the duration of the experiment, food intakes of the groups fed the higher protein diets improved on successive days; the length and severity of the depression were proportional to the protein content of the diet fed. Rats fed low levels of protein grew poorly, and their food intake remained depressed. The gradual improvement in growth and food intake of rats fed diets containing more than 35% casein was accompanied by dramatic increases in the activities of serine-threonine dehydratase (SDH, EC 4.2.1.16) and glutamate-pyruvate aminotransferase (GPT, EC 2.6.1.1) in liver. The increase in amino acid catabolic activity was accompanied by decreases in the concentrations of most amino acids in plasma and brain. However, concentrations of branched-chain amino acids, in both plasma and brain, increased in direct proportion to the protein concentration of the diet fed. As a result of these reciprocal responses, the total concentration of indispensable amino acids in brain (IAA) was maintained within a narrow range of values, despite a sixfold range of protein intakes. Whole-brain concentrations of norepinephrine, dopamine and serotonin were not correlated with dietary protein concentration, total food intake or protein intake. Brain concentrations of homovanillic acid and 5-hydroxyindoleacetic acid were correlated inversely with protein intake and that of 3,4-dihydroxyphenylacetic acid was correlated directly with food intake. Protein intake appeared to be related to the animal's ability to maintain brain total IAA content between some upper and lower limits. Our results indicate that this was accomplished initially through downward adjustment of protein intake and subsequently through an increase in catabolic capacity for the amino acids.     

Regulation of rat liver branched-chain alpha-keto acid dehydrogenase activity by meal frequency and dietary protein

Effects of feeding frequency on liver branched-chain alpha-keto acid dehydrogenase (BCKAD) activity are unknown. In the present study, rats were trained to consume their daily allotment of food in 6 h (meal-feeding). Rats were fed diets containing 0, 9, 25 or 50% casein and after 10 d were killed before or 3 h after the meal. The enzyme in rats fed diets containing 0, 9 and 25% casein was activated three- to sixfold after meal consumption. Previous studies showed that the liver enzyme is essentially fully activated in post-absorptive rats fed an adequate protein diet ad libitum. Meal-feeding an adequate protein (25% casein) diet resulted in a marked decrease in the postabsorptive percentage of active complex compared to ad libitum feeding of the same diet (29 +/- 6% vs. 93 +/- 6% active). Administration of alpha-ketoisocaproate (200 mumol/100 g body weight, an inhibitor of BCKAD kinase) reversed the meal-feeding-induced inactivation of the complex within 10 min. We conclude that the frequency of food intake, in addition to the level of dietary protein, influences the proportion of liver BCKAD in the active state. Inactivation of hepatic BCKAD in rats trained to feed once a day may be an adaptive mechanism that results in increased efficiency of branched-chain amino acid utilization between meals.     

Zinc deficiency increases the osmotic fragility of rat erythrocytes

Zinc deficiency in rats causes increased osmotic fragility of their erythrocytes. This study was designed to determine the relationship of food intake and dietary sulfur amino acid level to the effect of low zinc status on fragility. Immature rats were fed for a 3-wk period a low zinc diet (less than 1 mg/kg) based on isolated soybean protein or a similar control diet (100 mg Zn/kg diet) supplied either ad libitum or by pair feeding. Fragility was measured by the degree of hemolysis in hypotonic saline solutions. In the first experiment, zinc deficiency resulted in higher fragility than in ad libitum controls; pair-fed controls were intermediate and not different from either. Experiment 2 included two levels of methionine, 0.4 and 0.9%, and two of zinc, 0 and 100 mg Zn/kg diet. At the 0.4%, but not at the 0.9% methionine level, hemolysis of red blood cells from the zinc-deficient rats was significantly greater than those from either pair-fed or ad libitum controls. Repletion for 1 or 2 d completely alleviated the increased fragility, but in vitro addition of zinc had no effect. Restricted intake of the zinc-adequate diet reversed the fragility within 1 d as readily as did ad libitum intake. Thus, the osmotic fragility induced by zinc deficiency was prevented by high sulfur amino acid intake and was readily reversed by dietary zinc. It is postulated that extracellular or membrane-bound zinc protects a component of the membrane that is essential to its function, and that reversal of the defect requires an in vivo metabolic process.     

Effect of diet restriction on some key enzymes tryptophan-NAD pathway in rats.

Dietary intake of rats was restricted by feeding varying amounts of a 20% protein diet. After 6 weeks of feeding, some key enzymes of the tryptophan and nicotinic acid-NAD pathway, liver nicotinamide nucleotide concentration, and urinary metabolites of tryptophan and nicotinic acid were studied. With an increase in diet restriction, liver tryptophan oxygenase (EC 1.13.1.12) activity increased. Quinolinate phosphoribosyltransferase (EC 2.4.2.a) activity, on the other hand, was found to decrease with moderate diet restriction up to 50% restriction, but increased again with more severe diet restriction in rats fed 25% of ad libitum intake. Liver nicotinate phosphoribosyltransferase (EC 2.4.2.11) activity was also observed to decrease with moderate diet restriction and did not further change when the restriction was severe while picolinate carboxylase (EC 4.1.1.45) activity increased significantly only in severe diet restriction. In rats fed 25% of ad libitum intake, urinary quinolinic acid excretion was low whereas N'-methylnicotinamide excretion was elevated. Alterations in the enzyme activities accompanied by changes in the levels of urinary metabolites, observed in the present study, suggest that the potential efficiency of conversion of tryptophan to nicotinamide nucleotides is not constant and is influenced by dietary intake.     

Regulation of glucose-6-phosphate dehydrogenase and malic enzyme in liver and adipose tissue: effect of dietary trilinolein level in starved-refed and ad libitum-fed rats.

The responses of glucose-6-phosphate dehydrogenase (G6PD) (EC 1.1.1.49) and malic enzyme (ME) (EC 1.1.1.40) were studied in liver and adipose tissue of rats fed for 2 days a high glucose diet containing levels of synthetic trilinolein ranging from 0 to 25% (w/w) of the diet (trilinolein was substituted for glucose). One group of rats was starved for 2 days before the trilinolein-containing diets were fed (starved-refed); a second group of rats was fed a fat-free diet for 7 days before the trilinolein-containing diets were fed (ad libitum). Liver G6PD activity decreased exponentially and liver ME activity decreased linearly with increasing dietary trilinolein in starved-refed rats, but did not decrease significantly in ad libitum fed rats. Total liver lipid decreased exponentially with increasing trilinolein in starved-refed rats, but increased exponentially in ad libitum fed rats. Adipose tissue G6PD and ME activities decreased slightly with increasing trilinolein in starved-refed rats, but did not decrease in ad libitum fed rats. When the data were adjusted by analysis of covariance for differences in glucose intake, the liver responses in starved-refed rats were still significant but the adipose tissue responses were not, indicating that the responses of adipose tissue (but not of liver) may have resulted from decreased glucose intake rather than from increased trilinolein intake. The results suggest that dietary trilinolein inhibits the characteristic increase in liver G6PD, ME and total lipids upon starvation-refeeding. However, after the levels of these parameters have been increased by feeding a fat-free diet they cannot be decreased by dietary trilinolein in 2 days.     

Effect of dietary zinc deficiency and the associated drop in voluntary food intake on rat erythrocyte membrane polyamines

The effect of dietary zinc deficiency in the rat on the free (noncovalently bound) polyamine concentrations in erythrocyte membranes, in erythrocyte cytosol and in the blood plasma were determined. Weanling male Wistar rats were fed an egg white-based diet containing less than 1.0 mg Zn/kg diet for 3 wk ad libitum. Control rats were either pair-fed or ad libitum-fed the basal diet supplemented with 100 mg Zn/kg diet. Tissue fractions were extracted with 0.2 M perchloric acid and polyamines were measured in the soluble fraction by dansylation, thin-layer chromatography and fluorescence spectrophotometry of the isolated dansylated polyamines. The depressed food intake associated with dietary zinc deficiency caused significantly (P less than 0.05) lower plasma spermidine, erythrocyte cytosol putrescine, spermidine and spermine and erythrocyte membrane spermidine concentrations. In addition, the depressed food intake caused significantly lower spermidine-spermine ratios in the erythrocyte membrane and cytosol and in blood plasma. Dietary zinc deficiency per se caused significantly (P less than 0.05) higher plasma spermidine and spermine and erythrocyte membrane spermine concentrations and significantly lower spermidine-spermine ratios in erythrocyte membrane and cytosol than in pair-fed, zinc-adequate controls.     

Stomach and upper intestine of the rat in the regulation of food intake.

The role of the upper intestine in the regulation of food intake and gastric emptying has been studied in normal, gastrectomized, and "crossover" rats, parabiotic rats with a common visceral cavity in which the proximal duodenum of each parabiont is anastomosed to the pylorus of the stomach of the partner. One rat of "crossover" pairs eats and the partner eats little or nothing. Normal rats fed a raw soybean (RS) diet ate less and gastric evacuation proceeded more slowly than in normal rats fed a heated soybean (HS) diet. It is postulated that RS contains a heat-labile intestinal irritant. The upper intestine of gastrectomized rats regulates food intake and prevents overloading of the intestine. Force feeding of excessive amounts of the RS diet elicited the secretion of much more solids and nitrogen into the upper intestine than did similar amounts of the HS diet. The upper intestines of "crossover" rats lose all control over entry of gastric contents into their duodena. Fed ad libitum, the parabiont whose stomach emptied first, ate continuously, while the recipient partner showed diarrhea. It is postulated that the control of food intake traditionally assigned to the stomach resides, rather, in the upper intestine.     

High levels of dietary amino and branched-chain alpha-keto acids alter plasma and brain amino acid concentrations in rats

Plasma and brain amino acid and plasma branched-chain alpha-keto acid (BCKA) concentrations were measured in rats fed diets containing high levels of individual amino and alpha-keto acids. Consumption of a low-protein (9% casein) diet high in leucine or alpha-ketoisocaproate depressed plasma concentrations of isoleucine and valine and their respective keto acids, alpha-keto-beta-methylvalerate and alpha-ketoisovalerate. High dietary levels of alpha-keto-beta-methylvalerate or alpha-ketoisovalerate (but not of isoleucine or valine) depressed plasma concentrations of the other BCKA and their respective branched-chain amino acids (BCAA). Consumption of a low protein, high phenylalanine diet depressed plasma concentrations of both BCAA and BCKA. Brain large neutral amino acid pools of rats fed all low-protein, high-amino acid diets were depleted. Consumption of diets high in individual BCKA increased brain concentrations of aromatic amino acids. In this study of rats allowed to feed for only 6 h/d, elevated brain phenylalanine concentration was associated with a significant depression of food intake, whereas elevated brain BCAA concentrations were not. Also, elevated plasma BCKA concentrations, comparable with those observed in maple syrup urine disease, were accompanied by elevations in concentrations of aromatic amino acids in brain but not in plasma.     

Chronic low intake of protein or vitamins increases the intestinal epithelial cell apoptosis in Wistar/NIN rats

OBJECTIVE: Malnutrition decreases antioxidant defense and increases oxidative stress in the intestine. We studied the effects of long-term restriction of food, protein, and vitamins on intestinal epithelial cell (IEC) apoptosis and the underlying mechanisms. METHODS: Weanling, Wistar/NIN male rats were fed ad libitum with a control diet, 75% protein-restricted diet, or 50% vitamin-restricted diet for 20 wk. The food-restricted group received 50% of the diet consumed by control rats. IEC apoptosis was monitored by morphometry, Annexin V binding, M30 CytoDeath assay, and DNA fragmentation. Structural and functional integrity of the villus were assessed by the ratio of villus height to crypt depth, and alkaline phosphatase and lys, ala-dipeptidyl aminopeptidase activities, respectively. Oxidative stress parameters, caspase-3 activity, and expression of Bcl-2 and Bax were determined to assess the probable mechanisms of altered apoptosis. RESULTS: Protein and vitamin restrictions but not food restriction significantly increased IEC apoptosis and only vitamin restriction altered structural and functional integrity of villi. Increased levels of protein carbonyls, thiobarbituric acid reactive substances, and caspase-3 activity along with decreased glutathione levels and Bcl-2 expression were observed in IECs of these rats, whereas food restriction did not affect these parameters. CONCLUSIONS: Protein restriction increased only IEC apoptosis, whereas vitamin restriction also affected the structure and function of villi. Modulation of the pathway mediated by mitochondria through increased oxidative stress appears to be the probable mechanism underlying this effect.