Relative contribution of cysteine and methionine to glutathione content and thyroid hormone levels in the rat

1. For a period of 24 d rats were given diets containing either casein or pea (Pisum sativum) protein at two different concentrations (180 and 120 g/kg) without or with cysteine or cysteine + methionine supplementation. 2. The effects of these diets on levels of blood and liver reduced glutathione (GSH) and serum thyroid hormones were studied. 3. When compared with the 180 g casein/kg diet, the 120 g casein/kg diet decreased liver GSH and serum thyroid hormone concentrations. These changes were related to dietary cysteine supply since supplementation induced an increase in these variables. 4. When compared with 180 g pea protein/kg diet, the 120 g pea protein/kg diet decreased liver GSH and serum thyroid hormone concentrations. These changes could not be corrected by cysteine or cysteine + methionine supplementation.     

The effect of graded levels of dietary casein, with or without methionine supplementation, on glutathione concentration in unstressed and endotoxin-treated rats

Glutathione (GSH) concentration was measured in rats fed either graded levels of dietary casein (experiment 1; 180 g, 120 g, 80 g, or 60 g protein/kg diet) or graded levels of dietary casein, supplemented with methionine to equalize dietary sulfur amino acid content to that seen in an 180 g/kg casein diet supplemented with 0.3 g L-methionine/kg diet (experiment 2; 180 g protein +0.3 g L-methionine, 80 g protein +6.70 g L-methionine, or 60 g protein +7.45 g L-methionine/kg diet). Rats were given an inflammatory challenge by intraperitoneal injection of endotoxin (lipopolysaccharide from Escherichia coli), and were compared with ad libitum and pair-fed controls. Glutathione concentration in various organs (liver, lung, spleen, and thymus) decreased in animals fed the low-protein diets (80 g or 60 g/kg diet). Addition of the sulfur amino acid, methionine, to the low-protein diets restored glutathione concentrations in animals fed ad libitum and prevented the fall in GSH concentration, which occurred in lung, spleen, and thymus in response to the endotoxin. Despite the similarity in the amount of sulfur amino acid consumed between the groups fed the 180 g protein +0.3 g L-methionine and the 60 g protein +7.45 g L-methionine/kg diet, in experiment 2, hepatic GSH concentration significantly increased in the latter group, in animals fed ad libitum and in the endotoxin-treated animals, but not in the pair-fed controls.     

Effect of wheat and Bengalgram diets on brain glutamate metabolism in postweanling rats

Six groups of five female rats each aged 6 weeks at start were fed different diets for a period of 15 days. The protein sources of diets used were: a) 10% casein: b) wheat: c) Bengalgram: d) wheat + lysine: and e) Bengalgram + methionine + cystine + tryptophan, all containing 1.6 g nitrogen/100 g, and f) 20% casein (3.2 g nitrogen/100 g diet). The group of five rats fed a 10% casein diet served as control. It was observed that total brain RNA, protein and free alpha amino nitrogen content and protein/DNA ratio were significantly decreased on wheat and Bengalgram diets as compared to the control. The specific activities of glutamine synthetase, glutaminase I, glutaminase II and glutamate decarboxylase and concentrations of aspartic acid, glutamic acid, glutamine and gamma-aminobutyric acid (GABA) in the brain were also decreased on wheat and Bengalgram diets. The fortification of wheat with lysine and of Bengalgram with methionine, cystine and tryptophan did not alter brain weight and DNA content. While brain RNA, protein free alpha amino nitrogen (F alpha AN) and activities of enzymes of glutamic acid metabolism and related amino acid levels were restored, the activity of enzyme glutamine transferase and alanine concentration remained unaltered on various diets fed. The observations on 20% casein diet showed that levels were similar to those observed on 10% casein diet.     

Effects on liver and serum lipids of dietary supplements of methionine and excess lysine given to previously-starved rats

The addition of lysine hydrochloride (50 g/kg) to a diet supplemented with methionine (3 g/kg) had no effect on liver lipids when rats (Wistar and Sprague-Dawley) were fed ad lib. for 14 d. However, refeeding a diet supplemented with methionine and excess lysine hydrochloride to previously-starved rats (Wistar) for 6, 7 or 9 d, but not 3 or 4 d, resulted in liver lipid accumulation, mainly triglycerides, which was prevented by the addition of arginine, citrulline, ornithine, adenine, allopurinol or maize oil, but not by guanine, cytosine, thymine or uracil. The addition of lysine hydrochloride to a methionine-supplemented diet resulted in reduced serum triglyceride levels after refeeding for 3 or 4 d and reduced serum cholesterol levels after refeeding for 3, 4 or 6 d. Serum lipids were unaffected by refeeding the diets for 7 or 9 d. Since hepatic lipid accumulation was preceded by the decline in the level of serum triglycerides, one of the factors responsible for lipid accumulation in the liver might be reduced transport of triglycerides from the liver into the blood. When adenine and allopurinol were added to the diet supplemented with methionine and lysine hydrochloride refed for 4 d, there was an increase in serum triglycerides. However, when this diet was refed for 7 d, with the addition of arginine, citrulline, guanine, pyrimidine bases, allopurinol or maize oil, no effects on serum cholesterol and triglyceride levels were observed.     

Effects of dietary proteins and trypsin inhibitor on growth and lipid metabolism in hamsters

The purpose of this study was to determine trypsin inhibitor (TI) activity in sweetpotato and soy flour diets and their effects on the growth and lipid metabolism of hamsters. Male Golden Syrian hamsters were fed different types of dietary protein containing casein, soyprotein, transgenic sweetpotato plus soy flour (TSPF+SF), nontransgenic sweetpotato (NTSPF) plus soy flour (NTSPF+SF), transgenic sweetpotato (TSPF) and nontransgenic sweetpotato flour for 28 days. The TI activity was highest in TSPF+SF (19.30 TIU/mg) and NTSPF+SF (17.20 TIU/mg) diets that induced growth retardation in animals, lowest in TSPF (5.80 TIU/mg) and NTSPF (5.50 TIU/mg) diets, which did not affect the growth of the animals, and negligible in casein (<1.00 TIU/mg) and soyprotein (2.00 TIU/mg) diets. Plasma total cholesterol (TC), high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C) and triglyceride (TG) concentrations were significantly higher in hamsters fed the casein diet compared to those fed the soy protein, TSPF+SF, NTSPF+SF, TSPF and NTSPF diets. A positive correlation was observed between plasma TC concentrations of hamsters and dietary methionine, lysine, leucine content and methionine/glycine ratios. Liver TC and TG concentrations of hamsters fed casein were significantly higher than those of all other diet groups. The supplementation of sweetpotato flour with soy flour increased both protein and TI activity in the diets and the lipid metabolism of hamsters were unaffected by TI activity.     

Effects of p-aminobenzoic acid, methionine, threonine and protein levels on susceptibility of mice to Plasmodium berghei

The effects of dietary p-aminobenzoic acid (PABA), protein, methionine and threonine on Plasmodium berghei infection in mice were investigated. Animals were fed diets containing 12 or 20% casein supplemented with PABA (0 or 2 mg/kg diet), methionine (0 or 15 mg/g casein) and threonine (0, 7.5, 27.5 or 47.5 mg/g casein). Percent mortality was lower in rats fed diets without PABA than in those fed diets containing PABA. All further experiments were conducted without supplemental PABA. While the mean day of death was greater in the groups fed 12% casein, percent mortality in these groups was nearly twofold higher than in the groups fed 20% casein. The presence or absence of 15 mg methionine per gram casein had no effect on percent mortality, mean day of death, or percent parasitemia, regardless of dietary casein level. Supplementation of threonine at any level to the 12% casein diet with supplemental methionine resulted in mortality rates similar to those from animals fed the 20% casein diets, but percent mortality was not altered by threonine in the absence of supplemental methionine. The mean day of death of animals fed 20% casein increased with increments of added threonine. Methionine had no influence on this phenomenon. It is concluded that the quantity of dietary protein and the quality of its amino acid composition can have profound effects on the susceptibility of mice to malaria.     

Choline is required by tilapia when methionine is not in excess

Choline is essential in diets fed to most young vertebrates, but previous studies did not confirm the essentiality of choline in diets fed to tilapia. Two experiments were conducted to evaluate the essentiality of dietary choline in such diets. The basal diet used in both experiments contained 32 g crude protein/100 g diet (10.1 g crude protein from casein and gelatin, and 21.9 g from a crystalline L-amino acid mixture). The total sulfur amino acid (TSAA) concentration of the basal diet was 0.28 g/100 g diet, Met:Cys 89:11. In Experiment 1, a 4x2 design was used in which crystalline L-methionine was added to the basal diet resulting in four levels of TSAA (0.28, 0.50, 0.75 or 1.0 g/100 g diet, Met:Cys 89:11, 94:6, 96:4, or 97:3, respectively). At each level of TSAA, diets also contained either 0 or 1 g choline/kg diet supplied as choline chloride. Weight gain, feed efficiency (FE) and serum methionine concentrations were significantly affected by dietary TSAA concentration, but not by dietary choline concentration or the interaction between TSAA and choline. Weight gain, feed efficiency and serum methionine concentrations indicated that the TSAA requirement was 0.5 g/100 g diet. In the second experiment, diets were formulated to contain either 0.28 or 0.5 g TSAA/100 g diet, Met:Cys 89:11 or 94:6, respectively, and graded levels of choline ranging from 1 to 4 g/kg diet in gradations of 1 g/kg. Dietary methionine significantly affected weight gain and FE, whereas dietary choline significantly affected weight gain, FE and survival, and the interaction of methionine and choline significantly affected weight gain. Fish fed diets containing 0.5 g TSAA/100 g diet and 3 g choline chloride/kg diet exhibited the highest weight gain, feed efficiency and survival. On the basis of these data, it seems clear that juvenile tilapia require choline in certain dietary formulations.     

The digestion of protein in young pigs and the utilization of dietary methionine

Forty pigs between 23 and 51 d of age were given ad lib. diets containing wheat and one of five protein concentrates: meat meal A, meat meal B, soya-bean meal, milk and lupins (Lupinus augustifolius). Twenty of these pigs were given indigestible markers from 51 to 56 d of age and were killed at 56 d of age. The diets containing meat meals A and B, soya-bean meal and milk contained 2.3 g total methionine/kg and the diet containing lupins contained 2.1 g/kg. A further forty pigs of the same age were given the same diets supplemented with 1 g synthetic methionine/kg. The weight gains and feed conversion ratios of the pigs given the diets containing 2.1-2.3 g methionine and 3.1-3.3 g methionine/kg were not significantly different. The weight gains of the pigs given lupins (2.1 g methionine/kg) were less than those of the pigs given the diets containing 2.3 g methionine/kg. The apparent digestibility of dry matter (DM) and nitrogen was less for the diets containing the meat meals (0.75 and 0.78 respectively) than for those containing the other protein concentrates (0.80 and 0.84). The retention times in the large intestine of the diets containing soya-bean meal and lupins were 965 and 1083 min which were greater than those of the diets containing the other protein concentrates, mean 732 min. The major site of N digestion and absorption for the diet containing milk was the area of the small intestine 25-50% of total length from the pylorus, while for the other protein concentrates the major site was 50-75% of its total length from the pylorus. The digestion and absorption of N in the large intestine was less (3.4%) for the diet containing milk than for those containing the other protein concentrates (7.5-11.3%). The apparent digestibility of the methionine to the ileum for the five diets ranged from 0.74 to 0.86 while the calculated retention of the apparently-absorbed methionine was 1.00. It was suggested that methionine digestibility could be used as an indicator of availability. The calculated retention of apparently absorbed N in the carcass was 0.71 for the pigs given the diet containing milk and 0.51-0.58 for the pigs given the other diets.     

Low-protein diet prevents tissue lipoprotein lipase activity increase in growing rats

The time course of changes in tissue lipolytic activities was studied in young rats during the consumption of a low-protein diet containing 50 g protein/kg (40 g wheat gluten +10 g casein/kg) for 28 d followed by balanced refeeding with 200 g protein/kg (160 g wheat gluten +40 g casein/kg) for 28 d. Lipoprotein lipase (LPL) activities were compared with the values of a control group fed a balanced diet containing 200 g protein/kg for 56 d. At the end of protein malnutrition period, the epididymal fat tissue LPL activity represented 36 %, and that of heart and gastrocnemius was 44 %, of those of the control group. These differences were accompanied by lower serum- and VLDL-triacylglycerols (TAG), respectively 47.6 % and 31 % of the control group values, probably resulting from reduced synthesis of VLDL-apolipoproteins (29 % of control group values), concomitant with liver lipid accumulation (4.8-fold) and little lipid storage in epididymal fat tissue. At day 2 of refeeding, there was no significant difference in liver and epididymal fat tissue LPL activities between experimental and control rats. At the end of the refeeding period, LPL activity of epididymal fat and liver lipolytic activity had increased and became similar to control group values. The consumption of a low-protein diet prevented the increase in extrahepatic LPL activities as observed in the control group. The alterations in LPL activity suggest that a low-protein diet limits lipid storage in adipose tissue due to reduced serum VLDL-TAG availability.     

Effects of cassava variety and processing on energy and protein digestibility and utilization by young children

Two varieties of cassava, processed as Nigerian fermented flour (gari) or as Brazilian flour (farinha), were fed to two groups of eight infants and young children, each group receiving both forms of one variety, with preceding, intervening and following casein control diets. The flours provided 50% of diet energy, with casein added to make 8% energy as protein, vegetable oils to make 20% as fat and corn syrup solids and sugar to make 72% carbohydrate (CHO) energy. Fecal wet weight increased (P less than 0.05) from approximately 100 g/d (casein diets) to means (+/- SD) of 202 +/- 72, 171 +/- 58, 154 +/- 46 and 190 +/- 67 g/d; dry weights from means of 14.7-18.3 g/d to means of 22.9-24.4 g/d (P less than 0.05); fecal energy from means of 50-60 kcal/d to means of 89-94 kcal/d (P less than 0.01); fetal fat was generally not affected; and fecal CHO nearly tripled (P less than 0.01) from approximately 4 to 12 g/d. Apparent nitrogen absorptions and retentions from the cassava + casein diets were modestly lower than from casein diets. Rates of weight gain were very variable and not significantly different by diet; serum albumin levels were essentially unchanged. The results with these flours were indistinguishable from each other and from those previously found with freeze-dried cassava flour in otherwise identical diets. Variety and processing method had no effect on the digestibility of cassava starch and oligosaccharides and on the great resistance to digestion and the water-holding capacity of cassava fiber.     

Effect of dietary protein and methionine on sulfite oxidase activity in rats

Sulfite oxidase catalyzes the oxidation of sulfite to sulfate. To investigate whether or not sulfite oxidase activity (EC 1.8.3.1) is regulated by the amount of sulfur from dietary protein or excess methionine, we fed rats diets containing 5, 10, 20 and 50% casein with or without excess methionine and measured sulfite oxidase activity in liver and intestinal mucosa. Hepatic sulfite oxidase activity was significantly lower in rats fed 5 or 10% casein diets and significantly higher in rats fed 50% casein than in rats fed the control diet containing 20% casein, but activity did not change in response to the addition of methionine at any level of protein. Sulfite oxidase activity in the intestinal mucosa was only 5% of that seen in liver and did not change in response to dietary protein or methionine. Activity did not change in rats fed low iron diets (5 mg Fe/kg diet) at any level of protein tested or in response to glycine. These results show that sulfite oxidase activity can adapt to different levels of dietary protein but is unaffected by the level of methionine, total amino nitrogen or iron in the diet.     

Amino acid oxidation by young pigs receiving diets with varying levels of sulphur amino acids

Piglets were weaned at 3 d of age and were introduced to liquid diets in which 400 g/kg protein was supplied as skim-milk powder and the balance as a mixture of free amino acids. The skim milk contributed 2.3 g methionine and 1.4 g cystine/kg diet; the experimental diets were made by supplementing these levels with free amino acids. The adequacy of the test level of the amino acid in the diet was assessed by measuring the oxidation of [1-14C]phenylalanine as an indicator of the partition of the essential amino acids between incorporation into protein and degradation. Radioactivity recovered as carbon dioxide was used as a measure of catabolism. Addition of 0.2, 0.4, 0.7, 1.2 and 1.7 g L-methionine/kg to a diet containing 5 g cystine and 3 g choline chloride/kg showed that phenylalanine catabolism was minimal for the diet with 2.7 g methionine/kg indicating that this is the dietary requirement for methionine to serve as a source of methionine residues for protein synthesis. Addition of D-methionine to produce a series of diets with graded levels of methionine showed that the D-isomer was less effective than the L-isomer in reducing phenylalanine catabolism: the addition of 0.8 g D-methionine/kg diet was needed to produce the same effect as 0.4 g L-methionine/kg diet showing that the replacement value of D-methionine for L-methionine was 50% in the young pig.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oligo-L-methionine and resistant protein promote cecal butyrate production in rats fed resistant starch and fructooligosaccharide.

We examined the role of resistant protein and peptides in promoting cecal butyrate production in rats fed rapidly fermentable carbohydrates. Rats were fed diets containing raw potato starch (RPS, 200 g/kg diet) or fructooligosaccharide (FOS, 60 g/kg diet) with casein, soy or rice protein (250 g/kg diet) for 13 d. In rats fed RPS with casein, the major cecal organic acid was acetate (441 micromol), but lactate and succinate were also found in considerable amounts (324 micromol). Succinate was the major cecal organic acid (235 micromol) in rats fed FOS with casein. When rice protein was fed with RPS, the contribution of lactate was significantly lower and that of propionate tended to be higher (P < 0.1) than in rats fed casein. In rats fed rice protein with FOS, cecal butyrate and acetate were greater and cecal succinate was lower than in rats fed casein with FOS (P < 0.05). Despite the similar amounts of undigested protein in rice and soy proteins, soy protein did not similarly affect cecal butyrate in rats fed FOS or RPS. In another experiment, rats were fed diets containing high amylose cornstarch (HAS, 200 g/kg diet) with casein, casein + oligo-L-methionine (OM, 3 g/kg diet), soy protein, soy protein + OM (3 g/kg diet) or rice protein (250 g/kg diet) for 10 d. OM (digestibility, 31%) was substituted for the same amount of casein. Rats fed rice protein had greater cecal butyrate than rats fed casein (P < 0.05). OM supplementation to casein or soy protein increased cecal butyrate compared with rats fed casein or soy protein alone (P < 0.05). These data support our hypothesis that resistant protein and peptides promote cecal butyrate production and suggest that the differing potency of rice and soy proteins in promoting cecal butyrate production might be explained in part by the different amino acid composition of resistant protein.     

Effect of amounts consumed on the digestion of cassava by young children

To determine whether increasing proportions of cassava could be consumed and satisfactorily digested, eight recovering malnourished children (20-38 mo old) received 25, 50 and 75% of their diet energy as freeze-dried cassava flour during 9-d periods, with intervening casein control diets. Enough casein was added to all cassava diets to bring protein energy to 8% of the total. When compared to the control diet, the 25% diet had no significant effect on consumption time or measures of protein and energy digestion. With the 50% diet, fecal wet and dry weights were moderately higher than with the 25% diet (196 +/- 44 and 24 +/- 4 vs. 121 +/- 36 and 16 +/- 3 g/d, respectively), as were fecal energy (89 +/- 16 vs. 63 +/- 16 kcal/d) and calculated carbohydrate (11 +/- 2 vs. 5 +/- 1 g/d); apparent nitrogen absorption (mostly from casein) was slightly lower (79 +/- 5 vs. 83 +/- 6%) and consumption time slightly higher (5-25, median 10, vs. 4-18, median 6 min/feeding). When energy from cassava was increased to 75%, fecal weights (240 +/- 49 and 31 +/- 5 g/d), energy (124 +/- 27 kcal/d) and carbohydrate (16 +/- 4 g/d) were all higher than when cassava provided 50 or 25% of energy. Consumption required 8-34, median 17 min/feeding and apparent nitrogen absorption was 76 +/- 6% of intake.(ABSTRACT TRUNCATED AT 250 WORDS)     

Utilization of ileal digestible amino acids by pigs: lysine

Two experiments were conducted to determine the utilization of ileal digestible lysine by pigs. In the first, the apparent ileal digestibility of amino acids in cottonseed meal, meat-and-bone meal and soya-bean meal was determined in pigs fitted with 'T'-shaped cannulas. In the second experiment, three lysine-deficient diets were formulated to 0.36 g ileal digestible lysine/MJ digestible energy (DE), with lysine contributed from the three protein concentrates as the only source of lysine in sugar-based diets. An additional three diets were formulated with supplements of lysine to verify that lysine was limiting in the first three diets. The growth performance and retention of lysine by pigs given the six diets over the 20-45 kg growth phase were then determined. The apparent ileal digestibility of lysine in the three protein concentrates (proportion of total) was: cottonseed meal 0.74, meat-and-bone meal 0.78, soya-bean meal 0.89. Growth rates (g/d) of the pigs given the three diets formulated to 0.36 g ileal digestible lysine/MJ DE were significantly different (P less than 0.001): cottonseed meal 377, meat-and-bone meal 492, soya-bean meal 541. The response of pigs to the addition of lysine confirmed that lysine was limiting in these diets. Crude protein (nitrogen x 6.25) deposited by the pigs was significantly higher (P less than 0.001) for those given soya-bean meal (77 g/d), relative to meat-and-bone meal (66 g/d) and cottonseed meal (38 g/d). The proportion of ileal digestible lysine retained by pigs given the three protein concentrates was: cottonseed meal 0.36, meat-and-bone meal 0.60, soya-bean meal 0.75. The results indicate that values for the ileal digestibility of lysine in protein concentrates are unsuitable in dietary formulations as the assay does not reflect the proportion of lysine that can be utilized by the pig. It appears that, with heat-processed meals, a considerable proportion of the lysine is absorbed in a form(s) that is (are) inefficiently utilized.     

Utilization of low quality roughages: effects of urea and protein supplements of differing solubility on digesta flows, intake and growth rate of cattle eating oaten chaff

1. Expt 1. Five 150 kg steers with ruminal, abomasal and ileal cannulas were given 3000 g oaten chaff daily plus pelleted supplement with no added nitrogen (diet A) of 50 g N/d as urea (diet B), casein (diet C), casein and formaldehyde-treated casein (HCHO-casein) (50:50 w/w; diet D) and HCHO-casein (diet E), in a 5 x 5 Latin square design. The basal diet and supplement were fed in eight equal increments at intervals of 3 h. Proportions of dry matter and organic matter digested in the stomach and whole tract were greater for diets B, C, D and E than for diet A. Total volatile fatty acid levels in the rumen and the proportion of acetic acid, were lower, and the proportion of propionic acid higher on diet A than on the other diets. Rumen ammonia levels were lower on diets A, D and E than on diets B and C. N flows at the abomasum, ileum and rectum were lower on diet A than on the other diets; abomasal flows and apparent intestinal absorptions of amino acids were higher on diets D and E than on diets A, B and C. Efficiencies of bacterial protein synthesis were 15, 15, 14, 13 and 12 g bacterial N/kg OM truly digested in the stomach on diets A, B, C, D and E respectively. 2. Expt 2. Forty 300 kg steers were fed oaten chaff ad lib. plus twice the amount of the same pelleted supplements as in Expt 1. Intake of oaten chaff was 23% higher with N supplements (diets B, C, D and E) than without (diet A). Live-weight gains were 356, 798, 843, 842 and 805 g/d on diets A, B, C, D and E respectively. 3. It was concluded that efficiency of bacterial protein synthesis was not limited by the supply of peptides and amino acids in the rumen, and that increases in amino acid availability in the intestines from feeding HCHO-casein did not increase food intake or live-weight gain.     

Plasma lipids and lipoproteins in normo- and in hyperlipidemic rabbits fed plant protein diets

The effect of a diet based on a plant protein mixture, on plasma lipids and lipoproteins was evaluated in normo-and in hyperlipidemic rabbits. The proteins comprising the experimental diet consisted of equal amounts of soy protein, cottonseed protein and wheat gluten, and was supplemented with lysine, methionine and threonine to their respective levels in casein which was the control diet. Each diet was served with (0.25%) and without cholesterol. The normolipidemic rabbits were fed the various diets for 55 days. When rendered hyperlipidemic, animals were pre-fed for 20 days the cholesterol containing casen diet and subsequently given the experimental diets for an additional 35 day period. The plant protein diet had a marked hypocholesterolemic effect, and induced a reduction in the cholesterol and in the protein VLDL + LDL to HDL ratios that were used as atherogenic parameters.     

Effect of excess dietary methionine on weight gain and plasma amino acids in kittens

Four groups of five kittens each were individually fed for 6 wk either a purified control diet containing 0.5% methionine (Met) (based on 18% casein supplemented with arginine, cystine and threonine) or one of three experimental diets containing an additional 2, 3 or 4% L-Met. The diets with added Met caused a reduction in food intake (FI) on the second day and a negative body weight gain (BWG), in proportion to the level of added Met. After 10 d, kittens fed the 2 and 3% Met diets increased their FI and had positive BWG. During the last 10 d of the experiment, the control, 2% Met and 3% Met groups had BWG of 28, 15 and 0 g/d, respectively. Kittens given the 4% Met diet showed no adaptation and continued to lose weight. In these kittens plasma concentration of Met was 50-70 times and cystathionine about three times greater than in control kittens. Four male kittens were fed the same 4% Met diet for 6 wk and then switched to a diet containing 4% L-Met plus 4% glycine (Gly) for 12 d. Average daily FI was 21.4 +/- 1.3 g with 4% Met and 48.5 +/- 2.5 g after the addition of Gly, and BWG went from negative to positive. These results indicate that growing kittens are more sensitive than rats to excess Met and have a limited adaptive capacity. Kittens did not grow normally when the diet contained 2% or more dietary Met, which was equivalent to 0.6 g Met/(kg body wt.d).     

Absorptive behavior of oligo-L-methionine and dietary proteins in a casein or soybean protein diet: porto-venous differences in amino acid concentrations in unrestrained rats

In a low casein methionine-deficient diet, supplementation with oligo-L-methionine (OM) has a similar improvement on rat growth to supplementation of free L-methionine. Rat growth is little improved, however, when OM is added to a low soybean protein isolate (SPI) diet. To evaluate the mechanisms of the different effects of OM supplementation, we observed intestinal absorption of OM added to either an 8 g/100 g casein diet or an 8 g/100 g SPI diet. Using portal and venous cannulated rats under unrestrained conditions, we evaluated OM absorption by subtracting methionine porto-venous differences after feeding the diets without OM from the values after feeding the diets with 3% added OM. OM absorption was faster after feeding the casein-based diet than after the SPI-based diet during the initial stages of the experiment only, but throughout the experiment there were greater increments of methionine concentrations in both portal and venous blood after the casein-based diet than after the SPI-based diet. We also discovered that amino acids from the dietary casein were absorbed faster than those from SPI, using the porto-venous difference of isoleucine as an indication. The larger increment of methionine concentrations in the blood after feeding of OM with a casein diet and the rapid absorption of amino acids from casein may result in much growth improvement in rats.