Eicosanoid synthesis and ornithine decarboxylase activity in mammary tumors of rats fed varying levels and types of N-3 and/or N-6 fatty acids

Virgin female Sprague-Dawley rats (50 days of age) were administered a single intragastric 10 mg dose of 7,12-dimethylbenz(a) anthracene (DMBA). Three weeks later they were placed on diets containing either 20% corn oil (CO), 20% primrose oil (PO), 20% black currant seed oil (BCO), 20% borage oil (BO), 15% menhaden oil plus 5% corn oil (15% MO + 5% CO), 10% menhaden oil plus 10% corn oil (10% MO + 10% CO), 5% menhaden oil plus 15% corn oil (5% MO + 15% CO) or 10% menhaden oil plus 10% borage oil (10% MO + 10% BO). Incidences of mammary tumors at 16 weeks post-DMBA were 80% in rats fed the CO diet, 84% in rats fed PO diet, 67% in rats fed BCO diet, 88% in rats fed BO diet, 60% in rats fed 15% MO + 5% CO diet, 67% in rats fed 10% MO + 10% CO diet, 83% in rats fed 5% MO + 15% CO diet, and 92% in rats fed 10% MO + 10% BO diet. Tumor multiplicity was lowest in PO-fed rats and highest in BO-fed rats. The tumor burden per tumor-bearing rat was lowest in rats fed the 15% MO + 5% CO, and 10% MO + 10% CO, diets and highest in those fed 20% BCO diet. Although body weight at 16 weeks post DMBA was not significantly different among the dietary groups, food intake was significantly greater in rats fed a diet containing 20% BO, or 5% MO + 15% CO.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of excess dietary phenylalanine on composition of cerebral lipids

Abstract— Concentrations in whole rat brains of lipids (total lipids, phospholipids, galactolipids, cholesterol, plasmalogens) and of proteolipid protein were not altered after feeding for 2 and 6 weeks of diets containing 5 per cent excess l -phenylalanine. After 2 weeks of diet with 7 per cent excess l -phenylalanine there was a slight reduction (5–10 per cent) in the concentrations in whole brain of cholesterol and galactolipids. No significant effects were noted in cerebral hemispheres after 3 weeks of diets with 7 per cent excess l -phenylalanine. In the 5 and 7 per cent supplemented groups of animals, the total amounts of the various lipids were initially reduced to levels which were within 10 per cent of those in diet-matched controls. The results for rats indicate that after 3 weeks of age only very moderate effects on accumulation of cerebral lipids can be produced by excess dietary l -phenylalanine fed at the most toxic levels of supplementation, while lower levels of dietary supplementation are without effect. The results suggest further that the more mature brain is resistant to alteration of deposition of myelin lipids by high levels of phenylalanine.     

Accumulation of histidine, 3-methylhistidine, and homocarnosine in the brains of protein-calorie deficient monkeys

Abstract— Seventeen monkeys (M. nemestrina and M. fascicularis) aged 10 months to about 5 yr were divided into two groups and fed either an adequate protein diet (20% casein) or a low-protein diet (2% casein). The diets were supplied to the animals in restricted amount (200 g/animal in two daily rations). In one experiment, the malnourished animals were initially fed a diet containiing 8 per cent protein and the protein content of the diet was gradually reduced over a period of 9 months, to 2 per cent. After about 3 months on the 2 per cent protein diet, the malnourished monkeys showed growth failure, severe anorexia, peri-ocular oedema, tremors of the head and limbs, atrophy of several visceral organs, fatty liver, hypoalbuminaemia, and depressed serum levels of many essential amino acids with an elevation of the ratio of non-essential to essential amino acids. These features are consistent with protein-calorie malnutrition. Examination of the brains revealed significant alterations in the levels of glycerophosphoethanolamine (—40 per cent), glutamic acid (—25 per cent), histidine (+230 per cent), homocamosine (+185 per cent), 3-methyl-histidine (+147 per cent), lysine (+55 per cent), phenylalanine (+33 per cent) and tyrosine (+26 per cent) in comparison to findings on the well-fed monkeys. The possible implications of elevated cerebral contents of homocarnosine in malnourished monkeys are discussed in the light of several reported human cases in whom neurological disorders are associated with increased histidine-containing dipeptides in the brain, CSF, blood and urine.     

Muscle hypertrophy in rats fed on a buckwheat protein extract.

Growing rats were examined for the influence of a buckwheat protein diet on muscle weight and protein. In experiment 1, the rats were fed on a diet containing either casein or a buckwheat protein extract (BWPE) as the protein source (10%, 20% or 30%) for 5 wk. The relative weights (g per kg of body wt) of the gastrocnemius, plantaris and soleus muscles were higher in the BWPE-fed animals than in the casein-fed ones, but were unaffected by the dietary level of protein. These differences were not associated with growth. In experiment 2, the rats were fed on either a casein or BWPE diet at the 20% protein level for 5 wk. BWPE intake significantly elevated the gastrocnemius muscle weight, carcass protein and water, and reduced carcass fat. These results demonstrate that BWPE consumption causes muscle hypertrophy, elevates carcass protein and water, and reduces body fat.     

A low protein-high carbohydrate diet decreases D2 dopamine receptor density in rat brain.

The property of D2 dopamine receptors in the rat brain was evaluated after long-term dietary manipulation. Groups of rats were pair-fed with equicaloric diet containing low protein (8%)-high carbohydrate, high protein (52%)-low carbohydrate and normal protein (20%) for 36 weeks. The low protein-high carbohydrate fed rats exhibited a significant decrease in the density (Bmax) of D2 dopamine receptor in the striatum (28%) and the mesolimbic regions (36%) with no apparent change in the receptor affinity (Kd). These findings suggest that long-term consumption of a low protein-high carbohydrate diet, by decreasing D2 dopamine receptor density, may be an important determinant of central dopaminergic function.     

Mannose and the ‘Crowding effect’ of Hymenolepis in rats

Hymenolepis diminuta from rats infected with 10 cysticercoids and fed on a diet containing 3% (w/w) mannose for 4 weeks were found to be, on average, much heavier in terms of dry weight (46 mg) than those from rats fed on diets containing an equivalent concentration of either galactose, glucose or fructose (18 mg). Subsequently, the numbers, egg production and dry weights of worms were determined from rats which had been infected with doses varying from 0 to 160 cysticercoids per rat and fed on diets containing either 0, 1, 4, or 8% mannose (w/w). Density-dependent decreases in both worm dry weight and egg production were detected at 5 weeks post-infection, but both the number of worms recovered and their prepatent period appeared to be independent of cysticercoid dose. Differences in the distribution pattern of individual worm dry weights were observed between rats harbouring low (1–15) and high (16–135) worm burdens. Worms recovered from rats infected with 10 cysticercoids and fed on a diet containing 4% mannose (w/w) for 3 weeks were found to be, on average, more than twice as heavy (37 mg) as those from rats fed on diets containing 1, 2, or 8% mannose (w/w) for equivalent periods of time (16 mg). The results indicate that the ‘crowding effect’ cannot be explained simply in terms of inter-worm competition for carbohydrate.     

Hepatic Subcellular Fractions Lipids in Rats Fed Millet (Sorghum vulgarie) at Different Protein Levels

Effect of feeding defatted millet (Sorghum vulgarie) flour at 5, 10 and 14.5% protein levels respectively for six weeks has been studied on rat liver mitochondrial, microsomal and supernatant fractions total lipids, cholesterol, triglycerides, total phospholipids, phosphatidyl choline and phosphatidyl ethanolamine. The results have been compared with rats fed casein at 10% level for the same period. The metabolism of liver subcellular fractions lipids of millet diet and casein diet fed rats has been studied by the incorporation of acetate-1-¹⁴C and . A significant increase in mitochondrial triglycerides of rats fed millet diet at 5 and 10% protein level, in microsomes of rats fed millet diet at 5, 10 and 15% protein levels and in supernatant fractions of rats fed millet diet at 5 and 15% protein levels was observed. A significant increase in total cholesterol in mitochondria and microsomes and a significant decrease in supernatant fraction of rats fed millet diet at 10% protein level was observed. A significant increase in mitochondrial total phospholipids, phosphatidyl choline and phosphatidyl ethanolamine in rats fed millet diet at 10% protein level and a decrease in these in rats fed millet diet at 5 per cent protein level was observed. In microsomes total phospholipids were increased in rats millet diet at 10% protein level and phosphatidyl choline was increased in rats fed millet diet at 15% protein level. Total phospholipids, phosphatidyl choline and phosphatidyl ethanolamine were significantly reduced in the supernatant fraction of rats fed millet at 10% protein level.

Incorporation of acetate-1-¹⁴C into nonsaponifiable fraction of mitochondria, microsomes and supernatant fractions of rats fed millet diet at 5 and 15 % protein levels was significantly greater, and in saponifiable fractions of the above subcellular fractions was greater in rats fed millet diet at 5 per cent protein level. The specific activity (counts/min/mg) of free cholesterol in mitochondria, microsomes and supernatant fractions of millet diet fed rats was significantly greater, whereas the specific activity of triglycerides was not significantly different from the controls. The acetate-1-¹⁴C specific activity of phosphatidyl choline and phosphatidyl ethanolamine was significantly greater in all the above subcellular fractions of millet diet fed rats (except of phosphatidyl choline in rats fed millet diet at 5 % protein level). The specific activities of phosphatidyl choline were significantly greater in mitochondria of rats fed millet diet at 5 % protein level and of phosphatidyl choline and phosphatidyl ethanolamine in microsomes and supernatant fractions of rats fed millet diet at 5 and 15% protein levels. The specific activities of phosphatidyl choline were significantly decreased in mitochondria and microsomes of rats fed millet diet at 10% protein level. The total acetate-1-¹⁴C activities (counts/min/g equivalent wet liver) of free and esterified cholesterol triglycerides, phosphatidyl choline and phosphatidyl ethanolamine showed that their synthesis from acetate-1-¹⁴C was either enhanced in millet diet fed rats or was comparable to the controls. The total activity of (counts/min/g equivalent wet liver) into phosphatidyl choline and phosphatidyl ethanolamine showed that their synthesis was decreased in microsomes of rats fed millet diet at 10% protein level, increased in rats fed millet diet at 5 and 15% protein levels.     

Effect of Feeding Millet (Sorghum vulgarie) Protein on Growth,Nucleic Acids and Proteins of Liver and Plasma of Rats

Effect of feeding millet (Sorghum vulgarie) at 5, 10 and 15 per cent protein levels respectively for a period of six weeks to rats on their liver DNA, RNA and proteins of liver, its subcellular fractions and plasma has been studied, and results compared with rats fed casein at 10 per cent level. Both liver DNA and RNA of rats fed millet at 5 per cent protein level were significantly increased. Liver proteins (mg/l00 g body weight) of rats fed millet at 5 and 10 per cent protein level were significantly increased and plasma proteins decreased. Incorporation of leucine-I-¹⁴C into both liver and plasma proteins of rats fed millet was significantly higher than the control.     

Protein metabolism in the small intestine of the ethanol-fed rat

The effects of chronic ethanol feeding on the small intestine were investigated in young rats. Rats were fed a nutritionally-adequate liquid diet, containing 36 per cent of total energy as ethanol (treated, n = 7), or isovolumetric amounts of the same diet in which ethanol was substituted by isocaloric glucose (controls, n = 7). After six weeks the wet weight and total tissue contents of protein, RNA and DNA were significantly reduced by 21 per cent, 23 per cent, 16 per cent and 28 per cent respectively, (p less than 0.014). Rates of protein synthesis were measured with L[4(3H)]phenylalanine and fractional rates (defined as the percentage of constituent tissue protein synthesised each hour, i.e. ks, % h-1) were calculated from the specific radioactivity of free phenylalanine in both tissue homogenates and plasma. Ethanol-feeding reduced ks by approx 10 per cent (p less than 0.181). The amount of protein synthesized unit-1 RNA was also reduced by approx 15 per cent (p less than 0.059) but the amount of protein synthesis unit-1 DNA was unaffected by ethanol-feeding (p less than 1.000). In contrast, the absolute rates of protein synthesis were reduced by approximately 30 per cent (p less than 0.022). It was concluded that, as the small intestine contributes to approx. 20-25 per cent of whole body synthesis these results may have an important effect on whole body nitrogen homeostasis and may have implications for the gastrointestinal effects of ethanol seen during chronic alcoholic abuse.     

Heligmosomoides polygyrus (Nematoda): the influence of dietary protein on the dynamics of repeated infection

The influence of the protein component in the diet of the host on the population dynamics of gastrointestinal helminth infection was studied by using a mouse-H. polygyrus experimental model. Mice fed a 2% (by mass) protein diet ad libitum maintained body weight during the experiment, but gained weight steadily when fed a diet containing 8% (by mass) protein. When repeatedly infected with 5, 10, 20 or 40 larvae every 2 weeks, the mice fed the 2% (by mass) protein diet accumulated adult worms in direct proportion to exposure to the infective stages. Under similar infection régimes, mice fed an 8% (by mass) protein diet acquired a partly effective immunity to reinfection by the nematode. Acquired immunity was principally manifest as a reduction in the survival of adult worms, although a slight increase in the mortality rate and/or the development time of the tissue-dwelling larval phase was observed. Worm fecundity per head was significantly depressed in hosts fed the 8% protein diet. In conclusion, in these experiments it is demonstrated that the nutritional status of the host can influence the population dynamics of helminth infection.     

The development of dermal lesions and alopecia in male rats fed rapeseed oil.

For 8 weeks 10 male weanling Sprague-Dawley rats were fed a semisynthetic diet containing by weight either 20% corn oil or rapeseed oils containing different amounts of erucic acid (Brassica napus var. Zephyr, 0.6%; B. napus var. Oro, 1.8%; B. campestris var. Span, 4.8%; or B. campestris var. Echo and Arlo, i.e., regular rapeseed oil, 23.6%). At 4-5 weeks after the experiment began, rats receiving the diets containing rapeseed oil showed evidence of alopecia and developed scaly, hemorrhagic, and necrotic tails, as well as scaliness of the feet, similar to the lesions described in essential fatty acid (EFA) deficiency. This condition became most severe between 5 and 8 weeks and had disappeared by 14 weeks. Fatty acid analysis of the diets and tissues of the animals did not reveal any evidence of EFA deficiency. It is suggested that these symptoms observed might be related to a possible inhibition of prostaglandin biosynthesis in rats fed rapeseed oils.     

ACETYLCHOLINE,CHOLINE AND CHOLINE ACETYLTRANSFERASE ACTIVITY IN THE DEVELOPING BRAIN OF NORMAL AND HYPOTHYROID RATS1

Abstract— Acetylcholine, choline and choline acetyltransferase activity were measured in the whole brains of normal and hypothyroid rats during development. At 1 day postpartum, brain acetylcholine was 73 per cent of adult levels. Propylthiouracil-induced hypothyroidism up to age 20 days did not alter brain acetylcholine concentrations, but at 30 days resulted in significantly decreased levels. At day 1, brain choline was 20 per cent higher than adult levels and decreased between days 8 and 10. In hypothyroid rats this phenomenon did not occur until days 15–20. At day 1 postnatally, choline acetyltransferase activity was only 7 per cent of adult levels, then between days 5 and 20 rose to 77 per cent of adult levels. Beginning at day 8, hypothyroidism resulted in significantly decreased enzyme levels. This effect could be reversed at day 17 by concurrent tri-iodothyronine substitution therapy. In hypothyroid rats, maximum brain choline acetyltransferase activity was 30 per cent less than normal adult levels.     

Effects of protein level, methionine supplementation and carbohydrate type of the diet on liver lipid and plasma free threonine contents in the lactating rat

Eight groups of 13-15 female rats were fed purified diets after littering. Four groups received a low protein (8% casein) diet (groups 8) and the others, a normal protein (20% casein) diet (groups 20). Carbohydrates were supplied either as starch (groups S) or as starch plus 40% fructose (groups F). Half the animals received a 0.4% methionine supplementation (groups M). Four or five dams per group were sacrificed on days 2, 7 and 14 after littering. The diet intake was increased by methionine supplementation, substitution of starch for fructose and increased protein content, mainly during the second week of lactation. This influenced weight variation of the dams and litter growth. On all days, the plasma levels of cholesterol esters, triglycerides and phospholipids were positively correlated with the dietary protein level. On days 7 and 14, the liver neutral lipid content was increased in rats fed the low protein diets supplemented with methionine (groups 8SM and 8FM) and the normal protein diets containing 40% fructose (groups 20F and 20FM). The plasma free threonine content was positively correlated with the protein level in the diet. On day 14, rats fed a low protein diet had a threonine deficiency, except those in groups 8S and 8F. The plasma free threonine content of these rats was not reduced, possibly due to an impaired utilization of this amino acid. The liver lipidosis observed during lactation, in contrast to that observed during growth with a low protein diet, was not due to a threonine deficiency.     

SUPPLEMENTATION OF A WHEAT BREAD DIET WITH LYSINE AND THREONINE: EFFECTS UPON INTRAUTERINE GROWTH AND BRAIN BIOCHEMISTRY

Abstract— During pregnancy, rats were fed either a standard chow diet, a wheat bread diet or a wheat bread diet supplemented with lysine and threonine. At birth, the offspring of the dams fed the supplemented diet differed from the chow fed animals only in having a smaller amount of protein in the combined cerebellum and brain stem area while the pups whose dams were fed the bread diet showed lower brain weights, deficits in protein in all brain parts and deficits in DNA in the cerebrum.     

The role of growth hormone and amino acids on brain protein synthesis in aged rats given proteins of different quantity and quality

Summary. The purpose of the present study was to determine whether the regulation of brain protein synthesis was mediated through changes in the plasma concentrations of insulin and growth hormone (GH), and whether the concentrations of amino acids in the brain and plasma regulate the brain protein synthesis when the quantity and quality of dietary protein is manipulated. Two experiments were done on three groups of aged rats given diets containing 20% casein, 5% casein or 0% casein (Experiment 1), and 20% casein, 20% gluten, or 20% gelatin (Experiment 2) for 1 d (only one 5-h period) after all rats were fed the 20% casein diet for 10 d (only 5-h feeding per day). The aggregation of brain ribosomes, the concentration in plasma GH, and the branched chain amino acids in the plasma and cerebral cortex declined with a decrease of quantity and quality of dietary protein. The concentration of plasma insulin did not differ among groups. The results suggest that the ingestion of a higher quantity and quality of dietary protein increases the concentrations of GH and several amino acids in aged rats, and that the concentrations of GH and amino acids are at least partly related to the mechanism by which the dietary protein affects brain protein synthesis in aged rats.     

Increased hepatic activity of inducible nitric oxide synthase in rats fed on a high-fat diet

The effects were examined of the dietary level of fat on the activity of inducible nitric oxide synthase (iNOS) in the liver of rats. In experiment 1, rats were fed on a diet containing 5% or 20% beef tallow or safflower oil for 32 d. The animals were given a subcutaneous injection of the carcinogen, 1,2-dimethylhydrazine (DMH), on d 4. The activity of hepatic iNOS was significantly elevated by the high-fat diet, but was unaffected by the dietary source of the fat examined. In experiment 2, rats were fed on a 5% or 20% beef tallow diet for 11 d or 32 d with or without the DMH treatment. Feeding the high-fat diet and DMH treatment caused higher activity of hepatic iNOS. In experiment 3, the high-fat diet elevated hepatic iNOS activity and the amount of its protein in the lipopolysaccharide-treated rats. The results suggest that hepatic NO production is enhanced by a high-fat diet.     

Substitution of dietary oleic acid for myristic acid increases the tissue storage of α-linolenic acid and the concentration of docosahexaenoic acid in the brain, red blood cells and plasma in the rat

Various strategies have been developed to increase the cellular level of (n-3) polyunsaturated fatty acids in animals and humans. In the present study, we investigated the effect of dietary myristic acid, which represents 9% to 12% of fatty acids in milk fat, on the storage of α-linolenic acid and its conversion to highly unsaturated (n-3) fatty acid derivatives. Five isocaloric diets were designed, containing equal amounts of α-linolenic acid (1.3% of dietary fatty acids, i.e. 0.3% of dietary energy) and linoleic acid (7.0% of fatty acids, i.e. 1.5% of energy). Myristic acid was supplied from traces to high levels (0%, 5%, 10%, 20% and 30% of fatty acids, i.e. 0% to 6.6% of energy). To keep the intake of total fat and other saturated fatty acids constant, substitution was made with decreasing levels of oleic acid (76.1% to 35.5% of fatty acids, i.e. 16.7% to 7.8% of energy) that is considered to be neutral in lipid metabolism. After 8 weeks, results on physiological parameters showed that total cholesterol and low-density lipoprotein-cholesterol did not differ in the diets containing 0%, 5% and 10% myristic acid, but were significantly higher in the diet containing 30% myristic acid. In all the tissues, a significant increasing effect of the substitution of oleic acid for myristic acid was shown on the level of both α-linolenic and linoleic acids. Compared with the rats fed the diet containing no myristic acid, docosahexaenoic acid significantly increased in the brain and red blood cells of the rats fed the diet with 30% myristic acid and in the plasma of the rats fed the diet with 20% myristic acid. Arachidonic acid also increased in the brain of the rats fed the diet with 30% myristic acid. By measuring Δ6-desaturase activity, we found a significant increase in the liver of the rats fed the diet containing 10% of myristic acid but no effect at higher levels of myristic acid. These results suggest that an increase in dietary myristic acid may contribute in increasing significantly the tissue storage of α-linolenic acid and the overall bioavailability of (n-3) polyunsaturated fatty acids in the brain, red blood cells and plasma, and that mechanisms other than the single Δ6-desaturase activity are involved in this effect.     

Effects of dietary oyster extract on lipid metabolism, blood pressure, and blood glucose in SD rats, hypertensive rats, and diabetic rats

Oyster extract was prepared by hydrolysis of oyster protein with proteases, Aloase (a protease from Bacillus subtilis), and Pancitase (a protease from Aspergillus oryzae). Rats were fed a diet containing 20% casein (the control diet) or 15% casein and 5% oyster extract (the oyster extract diet) as the protein source. The oyster extract diet exerted a significant reduction in serum cholesterol and liver triglyceride concentrations as compared with the control diet in Sprague-Dawley (SD) rats fed cholesterol-supplemented diets for 4 weeks. The activities of cytosolic fatty acid synthase and glucose-6-phosphate dehydrogenase were significantly lower in the oyster extract group than in the control group in the liver of SD rats. Hepatic cholesterol and triglyceride concentrations were significantly lower in spontaneously hypertensive (SH) rats and Otsuka Long-Evans Tokushima Fatty (OLETF) rats, type 2 diabetic rats, fed the oyster extract diet, for 4 weeks and 4 months respectively, than in those fed the control diet in the cholesterol-free diet. Blood pressure was significantly lower in the oyster extract group than in the control group at the 2nd and 4th weeks after the beginning of feeding experimental diets in SH rats. These results suggest that oyster extract prepared by hydrolysis of oyster induces triglyceride-lowering activity in the liver through a decrease in hepatic lipogenesis in SD rats, and that it exerts the antihypertensive effect in SH rats.     

Recovery from galactose-induced neurotoxicity in the chick by the administration of glucose

Abstract— Chicks fed a diet containing 40% (w/w) galactose demonstrated convulsive activity after 52–54 h. However, they recovered from both physical and biochemical symptoms temporarily, following the intraperitoneal injection of glucose. The previously decreased levels of ATP and elevated levels of AMP in the brains of chicks fed galactose returned to normal within 20 min following the glucose treatment. During the recovery phase, plasma glucose content rose and brain glucose returned to the normal range, whereas the levels of brain galactose and its metabolites, galactitol and galactose 1-phosphate, were unchanged. Moderate plasma hyperasmolality was induced in chicks fed the diet containing galactose and xylose or saline in the drinking water. Neurotoxicity was observed only in the group fed galactose, although brain glucose and glycogen were reduced in chicks fed xylose. In the brains of chicks fed xylose, xylitol was identified by gas-liquid chromatography and mass spectrometry, and the amount was approximately 10 per cent of the amount of xylose simultaneously found in the brain. These studies support the viewpoint that dietary galactose exerts its acute neurotoxicity in chicks primarily by inhibition of glucose transport across the blood-brain barrier.     

Effects of Sulfur-containing Amino Acids and Glycine on Plasma Cholesterol Level in Rats Fed on a High Cholesterol Diet

The effects of the addition of individual amino acids on methionine-induced hypercholesterolemia (experiment 1), and the interacting effects of dietary protein level and sulfur-containing amino acids and glycine on plasma cholesterol concentration (experiment 2) were studied in growing rats fed on a high cholesterol diet. In experiment 1, rats were fed on a 25% casein-0.75% methionine (25CM) diet containing 2.5% of individual amino acids for 2 weeks. Methionine-induced hypercholesterolemia was prevented by the concurrent addition of glycine or serine, but the other amino acids tested (alanine, threonine, leucine, phenylalanine, lysine, arginine, and glutamic acid) had no effect. Histidine rather enhanced the hypercholesterolemia. In experiment 2, rats were fed on a 10%, 25%, or 50% casein diet containing 0.75% methionine, 0.60% cystine, 0.63% taurine, 2.5% glycine, or 0.75% methionine +2.5% glycine for 3 weeks. Dietary addition of 0.75% methionine increased the plasma cholesterol concentration for the 25% and 50% casein diets, but it decreased the plasma cholesterol for the 10% casein diet. When the addition level of methionine was doubled in the 10% casein diet, the plasma cholesterol concentration was significantly higher for the 1.5% methionine-added diet than for the 0.75% methionine-added diet. Cystine and taurine lowered plasma cholesterol for all dietary casein levels. Methionine-induced hypercholesterolemia with 25% and 50% casein diets was prevented by the glycine supplementation. These data suggest that sulfur-containing amino acids and glycine are important in plasma cholesterol regulation.