CONSUMPTION of a carbohydrate-rich, protein-free

Transcription

1 Meal Cmpsitin and Plasma Amin Acid Ratis: Effect f Varius Prteins r Carbhydrates, and f Varius Prtein Cncentratins Hidehik Ykgshi and Richard J. Wurtman We examined the effects f meals cntaining varius prteins and carbhydrates. and f thse cntaining varius prprtins f prtein (0% t 20% f a meal. by weight) r f carbhydrate (0% t 75%). n plasma levels f certain large neutral amin acids (LNAA) in rats previusly fasted fr 19 hurs. We als calculated the plasma tryptphan ratis Ithe rati f the plasma trytphan cncentratin t the summed cncentratins f the ther large neutral amin acids) and ther plasma amin acid ratis. (The plasma tryptphan rati has been shwn t determine brain tryptphan levels and. thereby. t affect the synthesis and release f the neurtransmitter sertnin). A meal cntaining 70% t 75% f an insulin-secreting carbhydrate (dextrse r dextrin) increased plasma insulin levels and the tryptphan rati; thse cntaining 0% r 25% carbhydrate failed t d s. Additin f as little as 5% casein t a 70% carbhydrate meal fully blcked the increase in the plasma tryptphan rati withut affecting the secretin f insulin-prbably by cntributing much larger quantities f the ther LNAA than f tryptphan t the bld. Dietary prteins differed in their ability t suppress the carbhydrate-induced rise in the plasma tryptphan rati. Additin f 10% casein. peanut meal. r gelatin fully blcked this increase. but lactalbumin failed t d s. and egg white did s nly partially. (Cnsumptin f the 10% gelatin meal als prduced a majr reductin in the plasma tyrsine rati. and may thereby have affected brain tyrsine levels and catechlamine synthesis.) These bservatins suggest that sertnin-releasing neurns in brains f fasted rats are capable f distinguishing (by their metablic effects) between meals pr in prtein but rich in carbhydrates that elicit insulin secretin. and all ther meals. The changes in brain sertnin caused by carbhydrate-rich. prtein-pr meals may affect subsequent fd chice and varius sertnin-mediated behavirs. II 1986 by Grune & Strattn, Inc. CONSUMPTION f a carbhydrate-rich, prtein-free meal by rats presumed t have an empty stmach increases brain tryptphan levels and the rates at which neurns prduce and release the neurtransmitter sertnin.i-3 In cntrast, cnsumptin f a meal cntaining 18% casein fails t increase brain tryptphan r sertnin, and higher prtein cncentratins may even decrease brain levels f these indles.4.5the effects f such meals n the brain are mediated by the changes that they prduce in plasma amin acid patterns. Carbhydrates elicit insulin secretin, and the hrmne markedly lwers plasma levels f mst large, neutral amin acids (LNAA), withut depressing thse f tryptphan6-li; as a cnsequence, tryptphan is better able t cmpete fr attachment t transprt macrmlecules in the capillary endthelia f the bld-brain barrier;2.13 and thereby t enter the brain. Dietary prteins cntribute sme tryptphan mlecules t the circulatin, thereby raising plasma tryptphan levels, hwever, they als cntribute far larger amunts f the ther, mre abundant LNAA, thereby lwering the plasma tryptphan rati.4.sthe ability f sertninergic neurns t prduce and release mre r less sertnin, depending primarily n what the individual happens t be digesting, allws these neurns t functin as "sensrs" f nutritinal and metablic state, prviding the rest f the brain with infrmatin that can influence such sertnin-dependent functins as cntrl f appetite;. sleep, ISmd;6 and perfrmance.17 Apparently n data are available n the prprtins f prteins that must be present in a meal in rder t blck the increase that its carbhydrate cntent wuld therwise prduce in the plasma tryptphan rati, nr in the prprtin f carbhydrates needed t cause the increase. Infrmatin is als lacking n the relative efficacies f varius natural prteins, especially thse the rat might be likely t eat. We have thus examined the changes in the plasma tryptphan rati prduced after rats fasted fr 19 hurs cnsume single meals cntaining 0% t 20% casein in the presence f varius amunts (0% t 75%) f carbhydrate, r thse cntaining fixed prprtins f a carbhydrate (70%) and ne f the fllwing prteins: casein, lactalbumin, egg white, peanut meal, and gelatin. We have als calculated the effects f the meals n ther plasma amin acid ratis, ie, thse knwn t determine brain levels f the ther LNAA.9 It will be shwn that adding as little as 5% f a high-quality prtein (casein) t a carbhydrate-rich meal can cmpletely blck its ability t increase the plasma tryptphan rati, but that individual dietary prteins differ cnsiderably in their ability t prduce this effect. MATERIALS AND METHODS Adult male Sprague-Dawley rats weighing abut 170 g (Charles River Breeding Labratries, Wilmingtn, Mass) were expsed t light (Vita-Lite, Dur- Test Crp, Nrth Bergen, NJ) between 9 PM and 9 AM daily, kept at a rm temperature f 22 C, and meal-fed a cmmercial stck diet (Charles River Rat, Muse and Hamster Maintenance Frmula) fr a five-hur perid (9 AM t 2 PM) nce a day fr tw weeks. On the day f an experiment, grups f five were given access t ne f several test diets, starting at 9 AM, and killed after tw hurs by decapitatin. Plasma samples were frzen (-20 C) until assay, and their amin acid cntents (including ttal Frm the Labratry f Neurendcrine Regulatin. Department f Applied Bilgical Sciences. Massachusetts InstitutefTechnlgy. Cambridge. Mass. Supprted in part by grants frm the Natinal Institutes f Health (NS-11131). the Natinal Aernautics and Space Administratin (NAG-l-l/O). and the Center fr Brain Sciences and Metablism Charitable Trust. Address reprint requests t R.J. Wurtman MD. Rm Massachusetts Institute f Technlgy. Cambridge. MA 1986 by Grune & Strattn. Inc. l6-0495/86/350f4jo I 0$03.00/0 Metablism. Vl 35. N 9 (September). 1986: pp

2 Table 1. Cmpsitin f Test Diets. and Radiimmunreactive Ttal Insulin Cntents in Plasma Calric Carbhydratet Prteinf Fat Cellulse Density RadiimmunreactiveInsulin Grup (%bywt) (%bywt) (%bywt) (% by wi) (calrie/g) (pu/mu Experiment (Fasting) :!: 1.4 (5) dextrin casein :!:0.7 (4)" dextrin casein :!:3.9 (5)" dextrin casein :!:5.3 (4)C 1.5 dextrin 10 casein :!: 1.9 (4)" dextrin 10 casein :!:4.0 (5)" dextrin 10 casein :!:5.7 (4)C 1.8 dextrin 20 casein :!: 1.8 (4)" dextrin 20 casein :!:3.1 (5)b dextrin 20 casein :!: 16.8 (3)C Experiment2 2.1 (Fasting) :!: 0.9 (5) dextrin casein :!: 4.2 (5)b dextrin 10 casein :!: 8.1 (5)' dextrin 20 casein :!: 5.5 (5)C dextrse casein :!: 3.7 (4)b dextrse 10 casein :!: 9.5 (5)C dextrse 20 casein :!: 6.0 (5)C Experiment (Fasting) :!: 1.2 (5) dextrse casein :!: 7.9 (5)b dextrse 2.5 casein :!: 6.4 (5)b dextrse 5 casein :!: 5.4 (5)b dextrse 10 casein :!: 14.6 (5)b dextrse 10 lactalbumin dextrse 10 egg white dextrse 10 peanut dextrse 10 gelatin Values in parentheses are number f test animals..aii diets cntain 4% salt mixture (Rgers QR. Harper AE: J Nutr 87: ) and 2.2% vitamin mixture. IICN Nutritinal Bichemicals. Cleveland). tamalz PFP starch. Rthstein Cmpany. Wburn. Mass. :j:teklad diets. A Harlan Sprague-Dawley Inc. C. Madisn. Wis. Crisc. Prcter & Gamble. Cincinnati. IIThis diet cntains apprximately 73% dextrin because f its minerals and vitamins. 1IMeans within a clumn nt fllwed (fr each experiment! by the same letter are significantly different (P < 0.05). Table 2. Effect f Changes in Dietary Casein and Dextrin f Plasma Amin Acid Cncentratins (Experiment 1). Fd Intake Tyrsine Tryptphan Phenylalanine Methinine Valine Leucine Isleucine Grup Diet fr 2 h (g) (nmi/ml) (nmi/ml) (nmi/ml) (nmi/mll (nmi/ml) (nmi/mu (nmi/ml) 1 Fasting % % % 2.0" 23.4 % % % % 3.9' 2 0% Casein/ 2.9 % % % 10.5" 36.8 % 0.7" 22.1 % 0.8" 82.8 % % % 2.gOc 0% Dextrin 3 0% Casein/ 3.9 % % % % % % 6.0" 59.4 % % % Dextrin 4 0% Casein/ 6.5 % % % % 2.0" 14.2 % % % % % Dextrin 5 10% Casein/ 5.8 % % 9.4b 84.0 % % 1.5' 42.9 % 2.0" % 5.7' % 4.8' 67.4 % % Dextrin 6 10% Casein/ 7.1 % % 5.0" 95.7 % 1.5' 56.6 % 1.5" 54.0 % 3.8* % 5.9" % 4.7' 66.4 % 2.0" 25% Dextrin 7 10% Casein/ 8.7 % % 10.2' 81.1 % 2.8" 59.2 % 2.3" 57.3 % 3.7" % 7.3' % 6.3c 56.6 % 4.5" 75 % Dextrin 8 20% Casein/ 5.4 % % 8.5' % % 3.0" 67.1 % % 7.9" % 6.5" % 2.4' 0% Dextrin 9 20% Casein/ 7.5 % % 9.g % % 3.5' % % % 10.0" % % Dextrin 10 20% Casein/ 7.8 % % 9.5" % % 3.8" % 4.9' % % % 2.2" 75% Dextrin r I Means:!: SEM f five rats per grup. Means within a clumn nt fllwed by the same letter are significantly different (P < 0.05)..'nitial bdy weight f rats. 165 :!: 6 g.

3 MEAL COMPOSITIONAND PLASMA AMINO ACIDS «~ J Q ~ 0.28 ~ 0.26 a: 0.24 c -a Q. 0.20,.,.= 0.18 ~ 0.16 a: Fast - 0 inq X %dextrindiet X 25 % dextrin diet % dextrin diet 10 Dietary Prtein Level ("!) Fig 1. Effect f dietary prtein level n plasma tryptphan ratis f rats fed 0%. 25%. r 75% carbhydrate diets. Significant differences (P < 0.05) are nted by a. b. and c (experiment 1). plasma tryptphans) were then measured by high-perfrmance liquid chrmatgraphy's (Waters Assciates, Milfrd, Mass). Three types f experiments were perfrmed. In the first, dietary carbhydrate and prtein cntents were varied systematically, and calric density was kept cnstant (at 3.94 calrie/g) by manipulating the fat cntent (Table I). In the secnd, we cmpared the effects f tw carbhydrates, dextrin and dextrse, n plasma amin acid respnses t dietary casein. Calric density was again kept cnstant by changing the fat cntents f the diet. In the third, we examined the effects f relatively lw amunts f several prteins n the changes in plasma amin acid levels caused by a high-carbhydrate meal; fat cntents were kept cnstant, sthat calric densities varied amng the diets (Table I). (In these experiments, brains were als assayed fr sertnin and its metablite 5-hydrxyindle acetic acid (5-HIAA) as described previusly.") All test diets were mixed with 20 the same weight f a 5% agar slutin. Plasma insulin cncentratins were measured by radiimmunassay using a duble antibdy methd (Immun Nuclear C, Stillwater, Minn). The statistical significance f differences between values was determined by analysis f variance and 95% cnfidence intervals based n pled standard deviatin (minitab-prgram). RESULTS Effect f Dietary Prtein Cntent n Plasma Amin Acid Respnses t Dietary Carbhydrate As shwn previusly; cnsumptin f a prtein-free, carbhydrate-cntaining meal decreased plasma levels f all f the LNAA, including tryptphan (Table 2); this effect was dse-related, such that it required a 75% carbhydrate meal t prduce significant reductins. The decreases in branched-chain amin acids tended t be greater than the decreases in the armatic LNAA, s that the high-carbhydrate, prtein-free meals als increased the plasma tryptphan rati. Cnsumptin f a meal lacking bth prtein and carbhydrate failed t change the plasma levels r ratis f any f the amin acids (Table 2). Additin f prtein t the diets caused dse-related increases in plasma levels f all f the LNAA, with greatest increases in methinine, valine, and leucine, and smallest increases in tryptphan and phenylalanine. As little as 10% prtein fully blcked an increase in tryptphan-lnaa ratis caused by eating the 75% carbhydrate meal (Fig I). Effect f Dietary Prtein Cntent n Plasma Amin Acid Respnses t Meals Rich in Dextrin r Dextrse Cnsumptin f prtein-free meals rich in dextrin (70%) caused significant reductins in plasma levels f methinine and the branched-chain amin acids; similar meals cntaining dextrse (70%) instead f dextrin als significantly reduced plasma levels f tyrsine, tryptphan, and phenylalanine (Table 3). Bth carbhydrates elevated the plasma tryptphan rati when cnsumed withut prtein (Table 4). Additin f 10%r 20% casein t the test diet blcked the decreases in plasma amin acid levels, and the increases in the plasma tryptphan rati assciated with eating the dextrin r the dextrse withut prtein (Table 4). Additin f Table 3. Effect f Casein Cntent n Plasma Amin Acid Cncentratins f Rats Given High Dextrin r Dextrse Diets (Experiment 2)" \ Fd Intake Tyrsine Tryptphan Phenylalanine Methinine Valine leucine Isleucine Grup Diet fr 2 h (gl (nml/rnli (nml/mli (nml/mli (nml/mli (nml/mli (nml/mli (nml/mli 1 Fasting :i: 2.8" 60.9 :i: 2.2' 35.3 :i: 2.9' 25.8 :i: 2.3' 85.5 :i: 4.3' 66.0 :i: 4.8' 36.1 :i: 2.1' 2 0% Casein/ 4.8:i: :i: :i: 3.5' 26.0 :i: :i: 1.6' 54.1 :i: 4.4' 37.5:i: 3.8" 19.1 :i: 1.8" 3 10% Casein/ 7.4:i: :i: 8.3' 68.4 :i: 5.4' 50.2 :i: 4.6' 58.9:i: 1.7d :i: 7.6d :i: 9.5' 57.2 :i: 2.9d 4 20% Casein/ 9.0 :i: :i: 4.3d :i: 3.6d 63.0 :i: 3.9'" :i: 2.0' :i: 2.4' :i: 7.8d 94.8:i: 1.9' 5 0% Casein/ 5:0:i: :i: 2.3' 39.6 :i: 4.4' 17.1 :i: 1.2' 9.8:i: 1.0' 32.7 :i: 2.1' 27.6 :i: 3.4' 12.9 :i: 1.5' 6 10% Casein/ 9.2:i: :i: 4.2' 87.0:i: 7.1' 52.3 :i: 4. l' 61.0:i: 3.2d :i: 2.9d :i: 5.3' 60.0 :i: 2.8d 7 20% Casein/ 10.5:i: :i: 10.7' :i: 4.9' 73.1 :i: 4.5d :i: 2.cf 303.0:i: 11.1' 223.2:i: 11.7" :i: 3.3' Means :i: SEM f fiva rats per grup. Means within a clumn nt fllwed by the same letter are significantly different (P < 0.05). "Initial bdy weight f rats, 168 :I: 5 g.

4 840 YOKOGOSHIAND WURTMAN Table 4. Effect f Casein Cntent n Plasma Amin Acid Ratis f Rats Given High Dextrin r Dextrse Diets (Experiment 21 Tyrsine/lNAA. Tryptphan/lNAA Phenylalanine/lNAA Valine/LNAA leucine/lnaa lsleucine/lnaa Grup Diet Ix IxI0-3) Ix 10-3) (x 10-» (x Ix 10-') 1 Fasting 134:1: 10' 235 :I: 12" 123:1: 5" 362:1: 12" 257 :I: 90b 127 :I: 9" 2 0% Casein! 152:1: 90b 341 :I: 25e 135 :I: 11e 321 :I: 110b 202 :I: 13' 94:1: 6' 3 10% Casein! 194 :I: 2ei' 146 :I: 5' 102 :I: 4" 425 :I: 1ge 272 :I: 10"" 120 :I: 3" 4 20% Casein! 188 :I: 7" 133 :I: 6' 76:1: 4' 442:1: 8e 319:1: 11" 119 :I: 2" 5 0% Casein! 130 :I: 17' 371 :l:40e 132:1: 6e 286 :I: 7' 246 :I: 470b 95 :I: Sb 6 10% Casein! 196 :I: 10"" 177 :I: 11' 100 :I: 10" 397 :I: 13" 261 :I: Sb 116:1: 5" 7 20% Casein! 239 :I: 14e 135 :I: 9' 77 :I: 30b 423 :I: 22" 279 :I: 110b 114 :I: 20b Means :I: SEM f five rats per grup. Means within a clumn nt fllwed by the same letter are significantly different (P < Sum f five lnaa f the fllwing six: tyrsine, tryptphan, pheytalanine, valine, leucine, isleucine. 20% casein t the diets als caused the plasma ratis f trysine and valine t rise significantly, and lwered that f phenylalanine. Effects f Varius Prteins r f Lw Cncentratins f Casein n Plasma Amin Acid Respnses t High-Carbhydrate Meal Mst f ur previus studies n meal-induced changes in the plasma tryptphan rati4-(i,9had utilized casein as the prtein surce. T determine whether the amin acid cmpsitin f a dietary prtein influenced its effect n plasma amin acid ratis, we cmpared the effects f relatively small amunts (10% by weight) f five different prteins n the increase in the plasma tryptphan rati that wuld therwise be prduced by a dextrse-rich meal. When rats ate the 10% casein diet, greatest prprtinate increases in plasma cncentratins were seen in tyrsine, methinine and isleucine (Table 5). The lactalbumin-cntaining diet had the greatest effects n tryptphan, but failed t elevate tyrsine r valine, and actually lwered phenylalanine. The egg white diet selectively elevated plasma tryptphan, methinine, valine, and isleucine; peanut meal raised nly plasma tyrsine and phenylalanine; and gelatin raised nly valine, significantly lwering phenylalanine and tyrsine. In general, the effects f each prtein n the plasma amin acid pattern tended t be crrelated with its wn amin acid cmpsitin.20hence lactalbumin, which is rich in tryptphan, raised plasma tryptphan levels while gelatin, which is pr in this amin acid, failed t d s. And egg white, which is rich in methinine, raised plasma methinine levels while peanut meal, which is pr in this amin acid, failed t d s. Our data, hwever, cannt be cnstrued as prviding definitive dcumentatin f this relatinship. Additin f 10% casein, peanut meal, r gelatin t the 70% carbhydrate meal blcked the expected increase in the plasma tryptphan rati, and casein r peanut meal increased the plasma tyrsine rati (Table 6). In cntrast, lactalbumin failed t blck the rise in the tryptphan rati r t increase that f tyrsine, and egg white nly partially suppressed the rise in the tryptphan rati. As lw a casein cncentratin as 2.5% partially blcked the rise in the plasma tryptphan rati caused by a carbhydrate-rich meal; a 5% casein cncentratin fully blcked this rise and als significantly elevated the plasma tyrsine rati (Table 6). Cnsumptin f the 70% dextrse meal elevated brain 5-HIAA levels (sertnin plus 5-HIAA) significantly, frm t ",gig (P < 0.05). Additin f 5% casein t the meal fully blcked this respnse ( ",gig). Diet Cmpsitin and Plasma Insulin Levels Radiimmunreactive ttal plasma insulin levels were elevated abut fivefld after cnsumptin f diets cntaining Table 5. Effect f Dietary Prteins n Plasma Amin Acid Cncentratins f Rats Given High Dextrse Diets (experiment 31- Fd Intake Tyrsine Tryptphan Phenylalanine Methinine Valine leucine Isleucine Grup Diet fr 2 h (g) (nml/mll (nmi/ml) Inml/mll (nmi/mll (nml!mll (nmi/mi.) (nmi/mi.) 1 Fasting 32.0:1: 2.7" 53.3 :I: 6.2" 32.7 :I: 2.cI' 26.8 :I: 1.7" 89.5 :I: 7.60< 78.9:1: 5.1e 36.6:1: 3.2" 2 0% Casein 8.5:1: :I: 2.9" 82.1:1: 6.8' 26.7:1: 1.8" 23.8 :I: :1: 2.1' 36.4 :I: 2.6' 23.0 :I:0.9' 3 2.5% Casein 10.0:1: :I: 3.90< 74.7 :I: 4.gb< 31.8:1: :I: 2.60< 75.2 :I: 6.1" 51.0:1: 3.8'" 29.0 :I: 2.4" 4 5% Casein 11.9:1: :I: 8.a< 73.7 :I: 2.40< 35.5 :I: :I: 2.0< :I: 4.5e 73.4 :I: 3.40< 37.0 :I: % Casein 10.9:1: :I: :I: 8.4' 49.3 :I: :I: :1: :I: 2.8" 64.4 :I: % lactalbumin 10.5:1: :I: :I: :I: 0.7' 43.1 :I: La< 78.1 :I: 4.g8' :I: :I: 4.0< 7 10% Egg white 9.4:1: :I: 5.0< :I: :I: :1: 7.4' :I: :I: 3.e/'< 61.1 :I: % Peanut meal 11.6:1: :1: 1.90< 60.2 :I: :I: 2.4e 13.9:1: 1.4' 83.5 :I: 6.9" 61.3 :I: 3.cI' 32.1 :I: 2.9" 9 10% Gelatin 8.1:1: :I: 0.8' 40.2 :I: 5.2' 37.3:1: 1.10< 19.0 :I: :1: 8.5' 71.1 :I: 3.60< 30.4 :I: 2.g8' Means :I: SEM f five rats per grup. Means within a clumn nt fllwed by the same letter are significantly different IP < Initial bdy weight f rats, 166 :I: 5 g.

5 MEAL COMPOSITIONAND PLASMA AMINO ACIDS 841 Tabla 6. Effect f Dietary Prteins n Plasma Amin Acid Ratis f Rats Given High Dextrsa Diets (Experiment 31 Tyrsine/LNAA. Tryptphan/LNAA Phenytalanine/LNAA Valine/LNAA Leucine/LNAA lsleucine/lnaa Grup Diet Ix 10-'1 Ix 10-" (x 10-') Ix 10-') (x 10-') (xi0-" 1 Fasting III:!: 98> 197 :!: 158> 113 :!: 4e 382:!: 8e 325:!: :!: 2b 2 0% Casein 102:!: 11' 475 :!: 32d 117 :!: 8e 333 :!: 23b 166:!: 11' l00:!: 3' 3 2.5% Casein 155:!: 19b 330 :!: 16e 118 :!: 5e 331 :!: 14b 204 :!: 10" 106 :!:5. 4 5% Casein 178 :!: 22b 244:!: 17b 103 :!: :!: :!: 6e 108 :!: 3' 5 10% Casein 184:!: 14b 185:!: 178> 94:!: 3b 393:!: 15e 264 :!: 3cd 127 :!: 2b 6 10% Lactalbumin 94 :!: 12' 369:!: 1ge 54:!: :!: 8' 436 :!: 19' 125 :!: 4b 7 10% Egg white 116 :!: 98> 278 :!: 11b 113 :!: 6e 464 :!: 9d 162 :!: 3' 137 :!: 2b 8 10% Peanut meal 183:!: 16b 225 :!: 10" 148 :!: 5d 337 :!: :!: :!: 6' 9 10% Gelatin 71 :!: :!: 13' 135 :!: 8d 590 :!: IS" 290 :!: 13d 105 :!: 4. Means:!: SEM f five rats per grup. Means within a clumn nt fllwed by the same latter are significantly different (P < 0.05)..Sum f five LNAA f the fllwing six: tyrsine, tryptphan, phenylalanine, valine, leucine, isleucine. I I, \ 70% t 75% f either dextrin r dextrse. They failed t rise significantly after meals cntaining 25% dextrin (Table I). Cnsumptin f meals cntaining 10%r 20% casein withut carbhydrate prduced small, statistically insignificant increases in plasma insulin, and additin f casein t a meal cntaining a given amunt f dextrin r dextrse failed t mdify the rise in insulin elicited by the carbhydrate. Because animals tended t cnsume smaller amunts f certain diets [(eg, thse lacking prtein (Tables 3 and 5), r thse lacking bth prtein and carbhydrates (Table 2)] than f thers, we perfrmed additinal pair-feeding studies t affirm that, under ur experimental cnditins, the effect f any diet n the plasma amin acid pattern was independent f the quantity that had been cnsumed prir t autpsy. In each pair-feeding study, fur diets were tested: the diet whse cnsumptin was expected t be least, the diet with greatest expected cnsumptin, and tw intermediate diets. In n case were the plasma amin acid patterns assciated with the pair-feeding paradigm different frm thse bserved after tw hurs f ad libitum feeding (and described in Tables 2, 3, and 5). These bservatins are cmpatible with the fact that all f ur animals had fd in their stmachs at autpsy, regardless f hw much fd they had eaten in the prir tw hurs. Similarly, preliminary studies were dne using the mst extreme diets (thse having the lwest and highest percentages f prtein and carbhydrate) t affirm that the amin acid patterns bserved after tw hurs f fd expsure wuld als have been seen at ther times. In these latter studies, grups f three animals were killed ne r tw hurs after being given access t the diets. In n case were the plasma amin acid patterns bserved after ne hur f feeding significantly different frm thse seen after tw hurs. DISCUSSION These bservatins shw that varius dietary prteins differ in their effects n the plasma tryptphan rati (and plasma LNAA levels) (Table 6); that nly very small cncentratins f sme prteins (as little as 5% casein, Table 6) are needed t blck the ability f dietary carbhydrate t elevate the plasma tryptphan rati; that the effects f the added prteins are nt due t suppressin f insulin secretin (Table 1); and that high-carbhydrate meals cntaining dextrin r dextrse are alike in their ability t raise the plasma tryptphan rati (Table 4) and t elicit insulin secretin (Table I). Since a substantial increase in the plasma tryptphan rati, as ccurs after cnsumptin f a carbhydrate-rich meal (Tables 4 and 6), invariably causes parallel increases in brain tryptphan levelsl,2 and in the synthesis and levels f the neurtransmitter sertnin,21.22ur data prvide additinal supprt fr the hypthesis that sertninergic neurns have a special rle as sensrs f fd-induced changes in plasma cmpsitin, ie, that they prduce mre r less f their signal, sertnin, depending n the cmpsitin f the fd that the rat is currently digesting.23other studies supprt the view that this infrmatin can be used by the rest f the brain in making chices abut the prprtins f carbhydrate t prtein in the next meal,24.25and that it can als affect ther sertnin-mediated behavirs like sleepiness, pain sensitivity, perfrmance, and md Based n ur earlier studies, we had anticipated bserving a linear inverse relatinship between the prprtin f prtein in a carbhydrate-rich meal and its effect n the plasma tryptphan rati. Our present bservatins suggest that in rats this is nt the case, and that prteins like casein exert differential effects n this rati nly within the relatively narrw range f 0% t 5%, beynd which they fully blck the increase in the rati that wuld therwise be caused by the carbhydrates). This suggests that the main use f the sertnin-releasing neurn may be t distinguish between tw classes f fds r meals, ie, thse cntaining very little prtein and large amunts f carbhydrate which raise the plasma tryptphan rati (fr example, rice r bread), and all ther fds. (As shwn in Fig I, a meal that is nt rich in carbhydrate will als fail t elevate the plasma tryptphan rati, whatever its prtein cntent.) Anther use fr the sertnin neurn in rats may be t distinguish amng prteins. A meal f lactalbumin plus carbhydrate wuld prbably be "read" by the brain as ne lacking significant amunts f prtein, while ne cntaining 5% r mre casein r peanut meal wuld be interpreted by sertninergic neurns as prtein-rich (Table 6). (Of curse, lactalbumin is nrmally cnsumed alng with casein). Gelatin, like casein, wuld als generate a signal (decreased sertnin release) characteristic f dietary prteins; hwever, it seems likely that the majr reductin that this prtein als causes in the

6 842 YOKOGOSHI AND WURTMAN plasma tyrsine rati wuld affect brain catechlamine release,26.27perhaps with additinal behaviral and physilgic cnsequences. The fact that an insulin-releasing nnsweet carbhydrate (dextrin) elicits the same changes in plasma insulin (Table 1) and the plasma tryptphan rati (Table 4) as a sweet, refined sugar (dextrse) supprts the hypthesis that the knwn actins f carbhydrates n brain cmpsitin are independent f their gustatry effects, and result frm their ability t elicit the secretin f insulin, which acts indirectly by changing the plasma amin acid pattern. It wuld nw be useful t cnduct studies like the present ne n human subjects, t determine whether in man (as in the rat) the plasma tryptphan rati distinguishes nly tw types f fds (carbhydrate-rich, prtein-pr vall thers), r respnds linearly t variatins in dietary prtein and carbhydrate cntents. REFERENCES 1. Fernstrm JD, Wurtman RJ: Elevatin f plasma tryptphan 14. Wurtman JJ, Wurtman RJ: Drugs that enhance central by insulin in the rat. Metablism 21: ,1972 sertninergic transmissin diminish elective carbhydrate cn- 2. Fernstrm JD, Wurtman RJ: Brain sertnin cntent: Increase sumptin by rats. Life Sci 24: , 1979 fllwing ingestin f carbhydrate diet. Science 174: , 15. Hartmann E: Effects f L-tryptphan n sleepiness and n 1971 sleep. J Psychiatr Res 17: ,1982/ Clmenares JL, Wurtman RJ, Fernstrm JD: Effect f ingest- 16. Lieberman HR, Crkin SH, Spring BJ, et al: Md, perfring a carbhydrate-fat meal n the levels and synthesis f 5- mance, and pain sensitivity: Changes induced by fd cnstituents. J hydrxyindles in varius regins f the rat central nervus system. J Psychiatr Res 17: , 1982/1983 Neurchem 25: , Spring BJ, Maller 0, Wurtman JJ, et al: Effects f prtein 4. Fernstrm JD, Wurtman RJ: Brain sertnin cntent: Physic- and carbhydrate meals n md and perfrmance. J Psychiatr Res lgical regulatin by plasma neutral amin acids. Science 178:414-17: ,1982/ , Fernstrm MH, Fernstrm JD: Rapid measurement f free 5. Wurtman RJ, Fernstrm JD: Cntrl f brain mnamine amin acids in serum and CSF using high perfrmance liquid synthesis by diet and plasma amin acids. Am J Clin Nutr 28:638- chrmatgraphy. Life Sci 29: , , Reinhard JF, Mskwitz MA, Sv AF, et al: A simple, 6: Fernstrm JD: Lann F, Wurtman R;J: C~relatlns.between sensitive and reliable assay fr sertnin and 5-HIAA in brain tissue bram try~t~han and. plas~a neutral amm acids fllwmg fd using liquid chrmatgraphy with electrchemical detectin. Life cnsumptin 10rats. LlfeScI13: , 1973 Sci 27: Wurt.man RJ, Fernstr~ JI?: Cntrl f.~rain neurtr~nsmit- 20. Atlas f ~rtein Sequence and Structure, vl 5, supplements tersynthesls by precursr availability and nutntlnal state. Blchem I 2 3 I. ts 1081 t. W h.,,, IS pr em sequences. as 109n, t DC, Nat. lnai PharmacI25: , Bimedical Research Fundatin, FernstrmJD, Faller DV,ShabshelwltzH: Acutereductins '".. fb d 5-HIAA r II. r 1. C 21. Fernstrm JD, Wurtman RJ: Bram sertmn cntent: PhysI ram sertmn an 10 w 109 IUV\JcnsumptIOn: rre-.. I t.. h h t. f h h f t. OIOglcaldependence n plasma tryptphan levels. SCience 173:149- a In Wit t era 100 serum tryptp an t t e sum 0 cmpe neutral amin acids. J Neural Transm 36: ,1975'.. 9. Fernstrm JD, Faller DV: Neutral amin acids in the brain: 22. Wurt~an RJ, Fernstrm JD: Effects f the diet n bram Changes in respnse t fd ingestin. J Neurchem 30: , neurtransmitters. Nutr Rev 32: , Theall CL, Wurtman JJ, Wurtman RJ: Self-selectin and 10. Fernstrm JD, Wurtman RJ, Hammarstrm-Wiklund B, et regulatin f prtein/carbhydrate rati in fds adult rats eat. J al: Diurnal variatins in plasma cncentratins f tryptphan, Nutr 114: ,1984 tyrsine, and ther neutral amin acids: Effect f dietary prtein 24. Wurtman JJ, Mses PL, Wurtman RJ: Prir carbhydrate intake. Am J Clin Nutr 32: , 1979 cnsumptin affects the amunt f carbhydrate that rats chse t 11. Madras BK, Chen EL, Fernstrm JD, et al: Dietary carb- eat. J Nutr 113:70-78, 1983 hydrate increases brain tryptphan and decreases serum-free tryptc- 25. Wurtman JJ, Wurtman RJ, Grwdn JH, et al: Carbhyphan. Nature 244:34-35,1973 drate craving in bese peple: Suppressin by treatments affecting 12. Pardridge WM: Regulatin f amin acid availability t the sertninergic transmissin. Int J Eating Dis 1:2-15, 1981 brain, in Wurtman RJ, Wurtman JJ (s): Nutritin and the Brain, 26. Scally MC, Ulus I, Wurtman RJ: Brain tyrsine levels vl 1. New Yrk, Raven, 1977, pp cntrl striatal dpamine synthesis in halperidl-treated rats. J 13. Pardridge WM: Kinetics f cmpetitive inhibitin f neutral Neural Transm 41:l--{i, 1977 amin acid transprt acrss the bld-brain barrier. J Neurchem 27. Wurtman RJ, Hefti F, Melamed E: Precursr cntrl f 28: ,1977 neurtransmitter synthesis. Pharmacl Rev 32: ,1980