Self-selection of Dietary Branched-chain Amino Acids by Rats

Transcription

1 Agric. Bidl. Chem., 51. (4), , Self-selection of Dietary Branched-chain Amino Acids by Rats Yukiko Yamamoto*and Keiichiro Muramatsu Laboratory of Food and Nutrition, Department of Agricultural Chemistry, Faculty of Agriculture, Shizuoka University, Shizuoka 422, Japan Received September 16, 1986 The ability of rats to regulate branched-chain amino acid intakes was investigated by a selfselection method. The relationship amongthe consumption of a branched-chain amino acid (BCAA), valine (Val), leucine (Leu), or isoleucine (He) and the amino acid concentrations in plasma and brain were also studied. Whenweanling rats were offered a choice of two diets containing different level ofval, Leu, or He, they consumed Val, Leu, or lie ranging from 0.53 to 2.07%, from 0.74 to 3.58%, and from 0.50 to 2.96% of the feed ingested, respectively. The amino acid concentrations in plasma and brain of the self-selecting rats were within a narrower range than those in the fixed rats. From these results it became clear that when rats were allowed to select their feed, they could regulate Val, Leu, or He intake to meet their requirement for the L-amino acid, and that these amino acid concentrations in plasma and brain were maintained within a narrow range. There have been studies on whether rats can regulate the intake of single amino acids by selecting between two solutions containing one or more amino acid(s).1"3) In this regard, Muramatsu and co-workers demonstrated that when rats were given a choice of two diets containing different amounts of lysine, methionine, phenylalanine, tryptophan, and threonine, they could regulate the intake of these amino acids and could maintain their maximum growth.4~8) The mechanism by which single amino acid intake is regulated in rats is not clear. We showedin previous reports that taste stimuli was not effective in the regulation of threonine selection,8) and that the relationship between phenylalanine or threonine intake and these amino acid concentrations in plasma and brain could not show a commonresult.6'8) In connection with the mechanism of regulation of food intake, numerous reports have shown two different results; the plasma or brain amino acid pattern maycontrol the food intake9~12) or not.13~16) This study was undertaken to find whether rats can regulate BCAA,i.e. Val, Leu, and He, intakes by the self-selection technique. The relationship between BCAAintakes and amino acid concentrations in plasma and brain was also studied. MATERIALS AND METHODS Animals and diets. Male weanlig rats of the Wistar strain,*1 28 days of age, were offered a 25% casein diet for 3 to 4 days before the experiments. They were separated into groups of4 rats for fixed groups and 5 rats for self-selection groups. Rats were individually housed in suspended screen-bottom cages (25 x 18 x 18cm) in a room maintained at 24± 1 C and lighted for 12hr daily (06: 00~ 18 : 00hr). The compositions of experimental diets are given in Table I. Rats of fixed groups were offered a single diet containing various amounts ofl- Val, L-Leu, or L-Ile; for the Val selection experiment, an amino acid mixture diet devoid of L-Val (10AA0V), an amino acid mixture diet with 0.3% L-Val (10AA0.3V), and * Present address: Department offood and Nutrition, Faculty of Science of Living, Osaka City University, Osaka, 558, Japan. ** Shizuoka Agricultural Cooperative Association for Laboratory Animals, Hamamatsu, Japan.

2 T T 1024 Y. Yamamotoand K. Muramatsu Table I. Composition of Experimental Diets. Aminoacid Diet Casein L-Valme L-Leucine L-I soleucine. mixture (%) Valine selection experiment 10AAOV * 10AA0.3V * 10C0.03V ** 10C1V ** 10C2V ** 10C3V ** Leucine selection experiment 10AA0L * 10AA0.37L * 10C ** 10C1L ** 10C2L ** 10C3L ** 10C5L ** Isoleucine selection experiment 10AA0I * 10AA0.25I ll.13* 10C0.05I ** 10C1I ** 10C2I ** 10C3I ** The diets also contained corn oil, 5.0; salt mixture,8* 5.0; vitamin mixture,8* 1.0; choline chloride, 0.1; and potato a- starch was added to make 100 percent. * L-Arg-HCl, 0.72; L-His, 0.3; L-Lys-HCl, 1.1; L-Tyr, 0.48; L-Phe, 0.44; L-Trp, 0.15; L-Cys, 0.03; L-Met, 0.57; L-Ser, 0.48; L-Thr, 0.5; L-Asp, 0.50; L-Gly, 0.16; L-Ala, 0.24; L-Pro, 0.94; and L-Glu was added to make 12.75% of total protein source. ** L-Arg-HCl, 0.34; L-His, 0.07; L-Lys-HCl, 0.34; L-Trp, 0.04; L-Met, 0.32; L-Thr, 0.15; l-g1u, a 10% casein plus amino acid mixture diet with 0.03, 1.0, 2.0, or 3.0% L-Val added (10C0.03V, 10C1V, 10C2V, 10C3V); for the Leu selection experiment, an amino acid mixture diet devoid of L-Leu (10AA0L), an amino acid mixture diet with 0.37% L-Leu (10AA0.37L), and a 10% casein plus amino acid mixture diet with 0, 1.0, 2.0, 3.0, or 5.0% L-Leu added (10C, 10C1L, 10C2L, 10C3L, 10C5L); for the Deselection experiment, an amino acid mixture diet devoid of L-Ile (10AA0I), an amino acid mixture diet containing 0.25% L-Ile (10AA0.25I), and a 10% casein plus amino acid mixture diet with 0.05, 1.0, 2.0, or 3.0% l- Ile added (10C0.05I, 10C1I, 10C2I, 10C3I). Rats of selfselection groups were offered a choice between these two diets; the 10AA0V or 10AA0.3V diet and the 10C0.03V, 10C1V, 10C2V, or 10C3V diet, and between the 10C0.03V diet and the 10C3V diet, for the Val selection experiment; between the 10AA0L diet and the 10C, 10C1L, 10C2L, 10C3L, or 10C5L diet, between the 10AA0.37L diet and the 10C1L, 10C2L, or 10C3L diet, and between the 10C diet and the 10C2L diet, for the Leu selection experiment; between the 10AA0I diet and the 10C0.05I, 1OC1I, 10C2I, or 10C3I diet, between the 10AA0.25I diet and the 10C0.05I, 10C1I, or 1OC3I diet, and between the 10C0.05I diet and the 10C3I diet, for the He selection experiment. Test diets and water were supplied ad libitum for 2 weeks. For the self-selection experiments, two diets werekept in opposite corners of the cage and were moved daily to prevent any positional effects. Growth and food intake were recorded daily, and food consumption was measured on a dry matter basis with correction for spillage. The amounts of ingested Val, Leu, or He were calculated from the amounts of food consumed. Amino acid measurement. When the experimental period was over, rats were anesthetized with ether and blood was obtained in a heparinized tube by heart puncture. Plasma was prepared by centrifugation and deproteinized with an equal volume of 6% sulfosalicilic acid (SSA). The brain was removed and homogenized with 2 volumes of 6%

3 Self-selection of Branched-chain Amino Acids 1025 SSA. Amino acid concentrations in plasma and brain were measured by the same method as in our previous report.7) RESULTS Body weight gain, food consumption, and aminoacid intake in rats offered diets containing various amount ofval, Leu, or He according to the fixed or self-selection method are shown in Tables II, III, and IV. In the Val selection experiment (Table II), when rats were fed by the fixed method, the rats fed the 10C0.03V, 10C1V, or 10C2V diet grew to the maximumlevel. The rats fed the 10AA0.3V or 10C3V diet grew significantly less, and weight loss was observed in rats fed the diet lacking Val (10AA0V). Food consumption of rats fed on the 10AA0Vor the 10AA0.3V diet was considerably less than other groups. Whenrats were offered a choice of two diets differing in Val content, there was no difference in the body weight gain and food consumption amongall groups, and was the same levels as those observed in rats fed the 10C0.03V, 10C1V, or 10C2V diet as a fixed diet, with the exception that rats offered a choice of the 10AA0.3V and 10C2V or 10C3V diet grew and ate significantly less. In the fixed groups of the Leu selection experiment (Table III), the growth of rats fed the IOC, 10C1L, 10C2L, 10C3L, or 10C5Ldiet was the maximumlevel. The rats fed the 10AA0.37L grew significantly less, and the body weight decreased in the rats fed the diet devoid of Leu (10AA0L). The rats fed on the 10AA0L, the 10AA0.37L, or the IOC diet ate significantly less than other groups. When rats were offered their diets by the selfselection methods, they grew and consumed their diets to the maximumlevel as did the rats fed the IOC, 10C1L, 10C2L, 10C3L, or 10C5L diet by the fixed method. Table II. The Effects of Fixed-ratio and Self-selection Feeding Methods on Body Weight Gain, Food Consumption and Valine Intake in Rats Offered Diets Differing in Valine Content Food consumption Bodyweight _,, c Valine Groups J. fc Foodpreference.. & gam Total. intake ^ intake (1) (2) Fixed (g/2 weeks) a) 10AA0V -12.8±0.6al 52.2±0.8a 0 b) 10AA0.3V 24.2±3.5b 116.6±6.4b 0.36±0.03 c) 10C0.03V 65.4±4.3C 148.7±3.6cf 0.91±0.03 d) 10C1V 59.5±3.7C 138.5±5.2cd 2.23±0.09 e) 10C2V 53.8±2.9cd 134.0±3.8de 3.56±0.12 f) 10C3V 48.0±2.1de 125.8±3.3be 4.64±0.ll Self-selection 1) (l)10aa0v vs. (2) 10C0.03V 58.4±2.4C 150.8±2.8cf 9.0± ± ±0.02 2) (1) 10AA0V vs.(2) 10CIV 59.6±2.1C 145.8±3.4cdf 33.7± ± ±0.02 3) (1) 10AA0V vs.(2) 10C2V 53.3±3.2cd 138.6±5.6cd 41.1± ± ±0.10 4) (1) 10AA0V w.(2) 10C3V. 53.7±2.2cd 137.1±3.9cd 57.9± ± ±0.21 5) (1) 10AA0.3Vvs. (2) 10C0.03V 57.9±1.2C 145.2±4.5cdf 40.7± ± ±0.02 6) (1) 10AA0.3Vvs. (2) 10C1V 57.6±2.3C 137.2±4.6cd 75.1± ± ±0.10 7) (1) 10AA0.3Vvs. (2) 10C2V 46.9±2.4dfe 132.5±3.2de 81.8± ± ±0.40 8) (1) 10AA0.3Vvs.(2) 10C3V 40.4±2.9e 128.8±4.5de 100.8± ± ±0.56 9) (1)10C0.03V vs.(2)10c3v 62.1±2.1C 149.4±2.9cf 146.0± ± ± Mean+SEM(n=4 for fixed groups and n=5 for self-selection groups). Values in the same column without commonsuperscripts are significantly different (/? <0.05).

4 1026 Y. Yamamotoand K. Muramatsu Table III. The Effects of Fixed-ratio and Self-selection Feeding Methods on Body Weight Gain, Food Consumption and Leucine Intake in Rats Offered Diets Differing in Leucine Content Food consumption Bodyweight _, c Leucine Groups ^ y. B Food preference. gain t * 1 à"* i intake & Total intake (1) (2) Fixed (g/2 weeks) a) 10AA0L -12.4±0.3al 61.6±2.la 0 b) 10AA0.37L 20.4±2.5b ±6.7b 0.43±0.03 c) IOC 56.4±1.7C 131.8±2.6C 1.13±0.02 d) 10C1L 58.2±2.8C 156.1±4.8de 3.00±0.09 e) 10C2L 58.5±5.3C 151.6±2.5d 4.51±0.08 f) 10C3L 56.4±2.3C 148.9±4.4df 6.00±0.17 g) 10C5L 52.6±4.5cd 149.0±5.9df 9.23±0.36 Self-selection 1) (1) 10AA0L vs.(2) 10C 57.8±2.0c 149.2±2.8df 6.4± ± ±0.02 2) (1)10AA0L vs.(2)10c1l 52.7±1.8cd 155.3±5.0de 19.9± ± ±0.10 3) (1) 10AA0L vs.(2) 10C2L 57.5±1.3C 162.3±4.0e 21.0± ± ±0.05 4) (1) 10AA0L vs.(2)10c3l 57.4±1.6C 149.9±3.0df 24.5± ± ±0.38 5) (1)10AA0L vs.(2)10c5l 54.0±1.0cd 155.5±6.0de 59.0± ± ±0.72 6) (1) 10AA0.37LV5.(2) 10C1L 54.0±1.3cd 154.9±3.7de 45.3± ± ±0.12 7) (1) 10AA0.37Lvs. (2) 10C2L 56.6±3.0c 162.3±5.5e 59.0± ll ±0.30 8) (1) 10AA0.37Lvs. (2) 10C3L 51.9±3.8cd 151.0±6.7d 83.6+ll ± ±0.46 9) (1) IOC -vs.(2) 10C2L 57.4±1.8C 140.0±4.0f 88.7± ± ± Mean+SEM(n=4 for fixed groups and n=5 for self-selection groups). Values in the same column without commonsuperscripts are significantly different (/> < 0.05). In the fixed groups of the He selection experiment (Table IV), rats fed the 10C0.05I diet grew to the maximum level, and rats fed the 10C1I, 10C2I, or 10C3I diet grew a little less. The growth of the rats fed the 10AA0.25I diet was significantly less, and weight loss was observed in rats fed the diet devoid of He (10AA0I). Food consumption of the 10AA0I group was significantly less than other all* groups. The rats offered a choice of two diets differing in He content grew to the same levels as those observed in rats fed the 10C0.05I, 10C1I, 10C2I, or 10C3I diet as a fixed ratio, with a exception that the rats offered a choice of the 10AA0.25I and 10C3I diet grew significantly less. Figure 1 shows the relationships between the Val, Leu, or lie intake and the body weight gain in rats fed by the fixed and the self-selection methods. Val, Leu, and He intakes of self-selecting rats ranged from 0.53 to 2.07%, from 0.74 to 3.58%, and from 0.50 to 2.96% of the food consumed, respectively. Aminoacid concentration. Relative concentrations of amino acid in the plasma of rats used for the Val, Leu, and He experiments are shown in Fig. 2. In the Val experiment, the Val concentration of the rats fed singly the 10AA0V or 10AA0.3V diet (a or b) was low, and it was elevated greatly in the rats fed the 10C1V, 10C2V, or 10C3V diet (d, e, or f), the value of the 10C3V group (f) reached 23.6 fold. The Val concentration in the plasma of self-selecting rats was kept within a narrower range than those of the fixed groups. The concentrations of other amino acids were not changed by the Val content in the diets or the methods, except that the threonine

5 Self-selection of Branched-chain Amino Acids 1027 Table IV. The Effects of Fixed-ratio and Self-selection Feeding Methods on Body Weight Gain, Food Consumption and Isoleucine Intake in Rats Offered Diets Differing in Isoleucine Content Food consumption _ Groups Body weight. Food, c preference Isoleucine.., Sain Total intake mtake (1) (2) Fixed (g/2 weeks) a) 10AA0I -16.1±0.3al 52.0±1.0a 0 b) 10AA0.25I 30.9±2.0b 139.3±4.4b 0.37±0.01 c) 10C0.05I 58.1 ±3.0c 142.7±3.0bc 0.88±0.02 d) 10C1I 49.9±0.7d 129.9±2.0bd 2.08±0.03 e) 10C2I 50.6± i.5d 130.4±2.2bd 3.48±0.06 f) 10C3I 51.2±1.9d 129.4±2.1bd 4.87±0.08 Self-selection 1) (l)loaaoi vs.(2) 10C0.05I 57.7±2.3C 140.8±5.3bc 5.6± ± 4.3 O.8O±O.O3 2) (1) 10AA0I vs.(2)10c1i 53.5±2.3cd 138.5±2.3bcd 25.7± ± ±0.ll 3) (1) 10AA0I vs.(2)10c2i 53.3±1.3cd 136.9±2.3bcd 30.0± ± ±0.08 4) (1) 10AA0I vs.(2) 10C3I 48.7±1.8d 133.1±3.6bd 28.6± ± ) (1) 10AA0.25Ivs.(2) 10C0.05I 61.6±1.8C 154.2±4.1e 33.4± ± ) (1) 10AA0.25I vs. (2) 10C1I 52.4±2.9cd 144.3±2.4bc 67.1± ± ±0.33 7) (1) 10AA0.25Ivs.(2) 10C3I 39.9±2.8e 143.1±2.9bc 123.5± ± ±0.23 8) (1) 10C0.05I vs.(2) 10C3I 56.1±3.3cd 137.9±4.7bcd ± ± Mean±SEM(n=4 for fixed groups and n=5 for self-selection groups). Values in the same column without commonsuperscripts are significantly different (/? < 0.05). concentration was elevated in the 10AA0Vand 10AA0.3V groups (a and b). In the Leu experiment, the Leu concentration in plasma of the rats fed singly the 10AA0Lor 10AA0.37L diet (a or b) was low, and it was elevated significantly in the rats fed the 10C1L, 10C2L, or 10C3L diet (d, e, or f). The Leu concentrations of all of the self-selecting groups were within a narrower range than those in fixed groups. Whenrats were fed a single diet containing various amounts of He, the He concentration in plasma was significantly lower in the rats fed the 10AA0I or 10AA0.25I diet (a or b), and was elevated greatly by the IOCII, 10C2I, or 10C3I diet (d, e, or f). The value of the group 10C3I (f) reached 10.5 fold. Plasma He concentration of the self-selecting groups changed within a narrower range than those of the fixed groups. Relative concentrations of brain amino acids in the rats are shown in Fig. 3. In the Val experiment, the Val concentration in rats, fed singly the 10AA0V or 10AA0.3V diet (a or b), was low, and was elevated greatly by the 10C1V, 10C2V, or 10C3V diet (d, e, or f). The Val concentration of all self-selecting groups was not changed as greatly as the fixed groups. In the Leu and He experiments, the amino acids concentrations in brain were not changed as much by the level of amino acid in the diets or method. DISCUSSION Our experiments demonstrated that rats offered a choice of two diets differing in Val, Leu, or He content could regulate Val, Leu, or lie intake, and gained their maximum growth with consumption of Val, Leu, or He ranging from 0.53 to 2.07%, from 0.74 to 3.58%, and from 0.50 to 2.96% of the diet ingested, respectively. These results support and extend our previous observations4~8) that rats can

6 1028 Y. Yamamotoand K. Muramatsu c 60- lj$a Ad XI CD / à" å¼ ^^ / Valine experiment _20[pa Valine in food consumed (%) fin-.c 9.xJ aax Af JH CD / 00 CD. / cd ^ <*/ Leucine experiment ^ >, 00 / A ^oiya,..,,, um hi. 00CD QI * ' Leucine in food consumed (%) t^^x, I Isoleucine experiment Isoleucine in food consumed (%) Fig. 1. The Effects of Fixed-ratio and Self-selection Feeding Methods on Valine, Leucine, or Isoleucine Intake and Body Weight Gain of Rats. Symbols used in the graph are listed in Table II for the valine experiment, in Table III for the leucine experiment and in Table IV for the isoleucine experiment. regulate lysine, methionine, phenylalanine, tryptophan, and threonine intakes by selfselection. The lowest Val intake (0.53%) of the selfselecting rats agreed closely with the Val requirement value of rats reported by RamaRao et al (0.55%)18) and Pick and Mead (0.50%),19) but much lower than the Val requirements of other reports (0.70% and 0.72%).2O'21) The lowest intake of Leu (0.74%) in self-selecting rats also agrees with the requirement in rats indicated by Rama Rao et al (0.70%),18) but was somewhat lower than the value reported by Williams et al (0.85%).21) The results of the lowest intake of He in self-selecting rats t (0.50%) closely agrees with the He requirements reported by Rose (0.50%),20) Williams et al (0.46%),21) and Rama Rao et al (0.55%).18) These results and our previous results4~8) on lysine, methionine, phenylalanine, tryptophan, and threonine indicate that the lowest values of the amino acid intake in self-selecting rats agree closely with the amino acid requirement, and then the self-selection technique would be useful for finding the amino acid requirements of growing rats. Fromthe data on plasma and brain amino acid concentrations, it became clear that when rats were self-selecting they could maintain Val, Leu, or He concentrations in plasma and brain within a narrow range and other amino acid concentrations were not muchchanged. The changes in aminoacid concentrations was more strictly limited in brain than in plasma, perhaps because of the existence of the bloodbrain barrier transport systems. These facts agree with our previous results in phenylalanine selection experiments, which showed that the phenylalanine and tyrosine concentrations in plasma and brain of rats that were self-selecting their food were not much changed as rats fed fixed diets.6) Val, Leu, and He are shown to be mutually antagonistic because of their structural similarity (12), and the changes in plasma concentrations of these aminoacids are knownas a striking biochemical manifestation of antagonism.2^ In this study, patterns of Val, Leu, and He in the plasma of fixed groups were changed by the dietary content of these amino acids, but not in an equilateral fashion (Fig. 2). When a high Val or He diet was fed, its concentration in plasma was increased (Val; 23.6-fold and He; 10.5-fold) but the other two amino acids stayed generally within the control range. On the other hand, excess dietary Leu did not increase the plasma Leu concentration so muchas the case of Val and lie (3.25-fold), but produced greater alterations in Val and He concentrations, perhaps by competition for absorption. The mechanisms which control the intake of

7 C/3 $L o" o W! S 3' >3 3' o 5r O5 a Fig. 2. The Effects offixed-ratio and Self-selection Feeding Methods on the Amino Acid Concentrations in Plasma of Rats. The symbols used in the graph are listed in Table II for the valine experiment, in Table III for the leucine experiment and in Table IV for the isoleucine experiment. These values are expressed as relative concentrations on the assumption that the valine concentration of group (c) in the valine experiment, the leucine concentration of group (c) in the leucine experiment and the isoleucine concentration of group (c) in the isoleucine experiment are 1.0.

8 Fig. 3. The Effects offixed-ratio and Self-selection Feeding Methods on the AminoAcid Concentrations in Brain of Rats. The symbols are listed in Table II for the valine experiment, in Table III for the leucine experiment and in Table IV for the isoleucine experiment. These values are relative concentrations as written in the legend of Fig. 2.

9 Self-selection of Branched-chain Amino Acids 1031 amino acids are not clear. Ashley and Anderson23' 24) observed an inverse correlation between the protein intake and the ratio in plasma of tryptophan to neutral amino acids (NAA) (phenylalanine, tyrosine, valine, leucine, and isoleucine), which is a good index of brain serotonin synthesis. Wurtman and Fernstrom25'26) have demonstrated that the ratios of tryptophan to NAAand tyrosine to NAAin plasma are influenced by the carbohydrate and protein intake. But Peters and Harper27) and Muramatsu et al.28) could not observe a consistent relationship between serotonin concentration in brain and protein intake in their recent reports. Some studies showed that plasma amino acid levels of patterns may be responsible for the regulation of amino acid intake. Leungand Rogers29)30) showed that the ventro-medial area of the hypothalamus is independent of the regulation of protein or amino acid intake, and suggested that certain prepyriform areas are responsible for an amino acid deficiency or amino acid imbalance, but not for excess amino acid. Our results in this report showed that Val, Leu, and He intakes appeared to be controlled at a level that would maintain plasma and brain concentrations between some upper and lower limits, and suggested that the concentration of the selected amino acid must be important in the control of amino acid intake. REFERENCES 1) W. C. Halstead and B. B. Gallagher, /. Compt. Physiol. PsychoL, 55, 107 (1962). 2) Q. R. Rogers and A. E. Harper, /. Compt. Physiol. PsychoL, 72, 66 (1970). 3) K. Kishi, F. Shizukaand G. Inoue, Rep. Res. Comm. Essent. Amino Acids (Japan), No. 96, 37 (1982). 4) K. Muramatsu and M. lshida, J. Nutr. Sci. Vitaminol, 28, 149 (1982). 5) K. Muramatsu and M. Ohya, Agric. Biol. Chem., 46, 1647 (1982). Y. Yamamoto, K. Makita and K. Muramatsu, J. Nutr. Sci. Vitaminol, 30, 273 (1984). K. Muramatsu, Y. Yamamoto and S. Tonooka, Rep. Res. Comm. Essent. Amino Acids (Japan), No. 104, 31 (1984). Y. Yamamoto, M. Suzuki and K. Muramatsu, Agric. Biol. Chem., 49, 2859 (1985). H. J. Almquist, Arch. Biochem. Biophys., 52, 197 (1954). H. L. Anderson, N. J. Benevenga and A. E, Harper, Am. J. PhysioL, 214, 1008<1968). P. Leung and Q. R. Rogers, Life Sci., 8, 1 (1969). A. E. Harper, N. J. Benevenga and. R. M. Wohlhueter, Physiol. Rev., 50, 428 (1970). Y. Peng, N. J. Benevenga and A. E. Harper, Am. J. Physiol., 216, 1020 (1969). Y. Peng and A. E. Harper, J. Nutr., 100, 429 (1970). H. L. Anderson, N. J. Benevenga and A. E. Harper, J. Nutr., 97, 463 (1969). H. L. Anderson, N. J. Benevenga and A. E. Harper, /. Nutr., 99, 184 (1969). A. E. Harper, /. Nutr., 68, 405 (1959). P. B. Rama Rao, V. C. Metta and B. C. Johnson, J. Nutr., 69, 387 (1959). R. T. Pick and R. J. Meade, /. Nutr., 101, 1241 (1971). W. C. Rose, Science, 86, 298 (1937). H. H. Williams, L. V. Curtin, J. Abraham, J. K. Loosli and L. A. Maynard, J. Biol. Chem., 208, 277 (1954). Q. R. Rogers, P. D. Spolter and A. E. Hafrper, Arch. Biochem. Biophys., 97, 497 (1962). D. V. M. Ashley and G. H. Anderson, /. Nutr., 105, 1412 (1975). G. H. Anderson and D. V. M. Ashley, Life Sci., 21, 1227 (1977). J. D. Fernstrom 1531 (1981). and D. V. Faller, J. Neurochem., 30, J. D. Fernstrom, F. Larin and R. J. Wurtman, Life Sci., 13, 517 (1973). J. C. Peters and A. E. Harper, J. Nutr., 115, 382 (1985). K. Muramatsu, S. Kawai and G. Ebis, Rep. Res. Comm. Essent. Amino Acids (Japan), No. 110, 36 (1986), Q. R. Rogers and P. M.-B. Leung, Fed. Proc, 320, 1709 (1973). P. M.-B. Leung and Q. R. Rogers, Am. J. Physiol, 111, 929 (1971).