Depressed Food Intake Research Articles

Nutritional value of naked oats (Avena nuda) in laying hen diets.

1. Two experiments were conducted to evaluate the use of naked oats (NO) in layer diets. In experiment 1 the use of NO supplemented with minerals, vitamins and lysine was examined. In experiment 2 layers were fed equicaloric and isonitrogenous diets containing 0-66% NO. 2. Layers fed ground NO supplemented with minerals, vitamins and lysine for 6 weeks exhibited a significant depression in food intake, egg production, egg weight and shell strength. 3. Substitution of NO at 20-66% resulted in performance comparable to that of birds fed a maize-soyabean meal diet for 12 weeks. Food intake was reduced in the first week of the experiment in birds fed diets with NO; thereafter, treatment effects were not detected. Yolk colour index progressively decreased as dietary inclusion of NO increased. 4. It is concluded that naked oats can be used at levels up to 66% in layer diets to replace all or part of the maize and part of the soyabean meal without any reduction in performance.

Effects of intraruminal infusions of sodium salts on selection of hay and concentrate foods by sheep

Infusion of salts of short-chain fatty acids into the rumen of sheep depresses food intake but the relative importance of the effect of the acids and of osmolality are not fully understood. Three experiments were carried out in which sodium acetate (NaAc) and sodium chloride (NaCl) were infused for 3 h at 4 m m/min and compared with water controls. The effects on the intakes of a concentrate food and hay were examined to study the effect of osmotic and acid manipulation of the rumen on dietary choice. In the first experiment the foods were continuously available while in the second and third the foods were given for 3 min at 1.5-h intervals. Salt infusions depressed concentrate intake without significant effect on the intake of hay. The effect of NaAc tended to be greater than that of NaCl and persisted after the end of infusion. The weight of concentrate eaten during the 3-min tests was significantly and negatively related to both acetate and sodium concentrations in rumen fluid. The weight of hay eaten was negatively related to concentrate intake. The results demonstrate that the treatments imposed had a differential effect on intake, only depressing that of the concentrate food. They also suggest that, as NaAc has a greater effect than NaCl, the influence on feeding is due both to the osmotic load and the acid effect.

Differentiation of the effects of protein status and acid-base balance on the appetite of sheep for lucerne silage

SUMMARYFive cross-bred Suffolk lambs (liveweight 24–29 kg) were fed lucerne silage and made acidotic or offered supplemental protein with the objective of determining the effects of acidosis and amino acid undersupply on food intake from silage. In this study, at McGill University, Quebec, Canada in January 1989, lucerne silage (25% DM) was supplemented with equimolar amounts (450 mmol/kg DM) of ammonium chloride, ammonium bicarbonate and sodium bicarbonate; fishmeal was added at 100 g/kg silage DM. The lambs were fedad libitumaccording to a 5 × 5 Latin square with 21-day periods.Digestibility of organic matter (OM) from silage ranged from 78 to 82% and was not significantly affected by diet (P> 0·05). Voluntary intake of digestible organic matter (DOM) from silage was. Fishmeal supplementation of lucerne silage improved nitrogen retention (P> 0·05) but not intake of DOM. The addition of ammonium chloride to silage reduced blood concentration (p< 0·05) and urinary output of HCO3, increased ammonia excretion in urine (P< 0·05), and depressed intake of DOM (P< 0·05). Ammonium bicarbonate also reduced voluntary intake of DOM (P< 0·05) but had no significant effect (P> 0·05) on the acid-base status of the lambs. Sodium bicarbonate depressed food intake but had no significant effect on measures of acid-base balance.The results suggest that metabolic acidosis is not an underlying mechanism restricting food intake by sheep and that neither acid-base imbalance nor inadequate protein status is likely to explain the limitation in food intake from ensiled lucerne.

Isoleucine requirements of the chicken: the effect of excess leucine and valine on the response to isoleucine.

1. Three experiments were designed to determine the response of broiler chickens to dietary isoleucine, and to quantify the antagonistic effects of excess leucine and valine on this response. 2. A dilution technique was used to measure the responses in growth rate and food intake to a range of diets differing in their isoleucine concentrations. A summit diet was formulated to contain isoleucine at 1.14 times the requirement and with leucine (1.76 times the requirement) and valine (1.87 times the requirement) at the minimum possible concentrations, given the ingredients available. A dilution mixture, devoid of protein, was formulated to correspond in all respects, other than in amino acid content, to the summit diet. These two basal diets were blended in different proportions to give a range of diets of decreasing isoleucine and protein content. 3. In experiment 1 the response was measured to isoleucine with leucine and valine remaining in the same proportion to isoleucine throughout the range of diets fed. In experiments 2 and 3, however, L-leucine and L-valine were added to the diets either singly or in combination to give 6 isoleucine concentrations and 3 ratios of each of leucine and valine to isoleucine. 4. Weight gain decreased as the isoleucine content of the diet was reduced, whereas food intake of broilers fed on the marginally deficient diets increased to a maximum and then decreased. FCE decreased curvilinearly as the isoleucine concentration in the food decreased, reflecting a concomitant change in the fat content of the broilers. 5. It is possible that the amount of dietary isoleucine assumed to be available to the broilers in these experiments was overestimated by hydrolysing the food samples for 72 h, and the doubt thus created makes an estimate of the efficiency of retention of isoleucine suspect. 6. Excess valine had no effect on the response to isoleucine, whereas an increase in the leucine to isoleucine ratio depressed food intake and hence weight gain, but only at the lowest concentrations of isoleucine. 7. If the food content of isoleucine is sufficient to meet the requirements of the broiler, relatively large excesses of leucine, of valine, or of both will not depress growth.

Abdominal chemo‐ and mechanosensitivity in ruminants and its role in the control of food intake

Ruminant animals have evolved a large and complex set of stomachs which allow fermentation of fibrous food by symbiotic micro-organisms. These stomachs are well innervated and generate signals which are thought to be important in the control of voluntary food intake. Tension receptors in the muscular wall of the rumen and reticulum are slowly adapting and provide a measure of distension while epithelial receptors are rapidly adapting and provide information on the fibrousness of the digesta; they are involved in the control of stomach motility and voluntary food intake in order to prevent excessive distension. The epithelial receptors are also sensitive to the chemical nature of the digesta, particularly acidity. There are mechano- and chemoreceptors in the abomasum (true stomach) and duodenum and chemoreceptors in the liver, all of which have been implicated in the control of intake. It is relatively easy to prepare and maintain ruminants with a rumen fistula and many studies have shown the effects of such manipulations as distension of balloons in the rumen on voluntary intake. With fibrous, slowly digested feeds intake is primarily limited by rumen distension. With more rapidly digested feeds, however, the products of digestion play an important role in controlling intake. Short-chain fatty acids are the main products of fermentation and infusion of their salts into the rumen depresses food intake to a much greater extent than infusion into the general circulation. Acetate or propionate given into the rumen are more effective, mole for mole, than butyrate but must be given at rates exceeding the natural rate of production in order to have a significant effect. It has been suggested that much of the effect of sodium acetate is via the increase in the osmolality of rumen fluid but there is considerable uncertainty as to the physiological significance of osmotic effects, especially when animals have free access to water and can prevent excessive increases in tonicity by increasing their water intake. Other constituents of rumen fluid have been implicated in the control of food intake, particularly lactic acid and nitrogenous compounds, especially as these can be found in fermented feeds such as silage. The omasum controls the flow of digesta to the abomasum; it is therefore well placed to control rumen fill and thus intake but there has been little study in this area and this is also true for the abomasum.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of the effect of dietary casein and cottonseed protein on food intake and growth in normal and tumorbearing rats

Male Fischer 344 rats with (tumor-bearers) and without (controls) a transplantable methylcholanthrene sarcoma were fed isonitrogenous, isoenergetic diets containing either casein or cottonseed protein (CSP) so as to compare the effects of these two proteins on the development of cancer-induced anorexia and cachexia. For both diets, tumor growth was associated with depressed food intake, decreased body weight, hypoalbuminemia and hyperlipidemia. Diet had no effect on food intake, weight gain or serum albumin for either controls or tumor-bearers; tumor weight was unaffected by type of dietary protein. Liver weights were lower for animals fed CSP than for those fed casein. Dietary CSP exerted a hypolipidemic effect in normal rats, but this differential effect of protein quality on serum lipids was abolished by tumor growth, as were differences in serum fatty acid profile associated with consumption of CSP. Tumor growth itself was associated with altered fatty acid profiles in serum, with the percentages of fatty acids as stearic and arachidonic acids being decreased and the percentages as oleic and linoleic acids being increased. Thus, dietary CSP has similar effects to casein on the development of cancer anorexia and cachexia in this animal model. The effects of protein quality on serum lipids, however, can be altered by tumor growth.

Effects of acute and chronic administration of Δ9-tetrahy-drocannabinol or cocaine on ethanol intake in a rat model

The acute and chronic administration of Δ 9-tetrahydrocannabinol ( Δ 9-THC) or cocaine were studied in rats trained to obtain all of their daily food by lever pressing during four equally-spaced 30-min periods with water and 5% or 7.5% ethanol solutions freely available. With 5% ethanol available, rats consumed almost all of their daily fluid intake as ethanol, while with 7.5% ethanol available, rats consumed water and ethanol solution in approximately equal amounts. Rats consumed more food pellets with 7.5% ethanol available than with 5% ethanol available. Acute administration of Δ 9-THC produced a dose-dependent decrease of 5% ethanol intake and food pellets consumed with a small increase in water intake, especially after the higher doses. Acute administration of Δ 9-THC also depressed food intake when 7.5% ethanol was available, but decreases in ethanol solution intake were small. Chronic administration of Δ 9-THC initially decreased ethanol intake, but tolerance occurred to this effect, so that during chronic Δ 9-THC administration ethanol intake not only recovered, but increased above control levels. When the chronic administration of Δ 9-THC was discontinued, ethanol intake was increased for 1 (5% ethanol) to 3 (7.5% ethanol) weeks. Animals with initially high, or initially low, but not with initially moderate ethanol intake, accounted for the increased ethanol intake during chronic Δ 9-THC administration and withdrawal. Acute cocaine administration, at doses up to 30 mg/kg, had little effect on eating and drinking; however, during chronic cocaine administration, ethanol intake gradually increased, an increase which was sustained during cocaine withdrawal. The increased ethanol drinking was confined to the first 6-h period after cocaine administration. These data suggest that the chronic administration and withdrawal of other drugs can increase ethanol intake in this rat model.

High Levels of Dietary Amino and Branched-Chain α-Keto Acids Alter Plasma and Brain Amino Acid Concentrations in Rats

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

Effects of triphenyltin acetate on pregnancy in rats by oral administration

A teratological test was carried out on triphenyltin acetate (TPTA) used as a fungicide and antifouling agent. Pregnant Wistar rats were treated orally with TPTA at dose levels of 0, 1.5, 3.0, 6.0, 9.0 and 12.0 mg/kg d during days 7–17 of gestation. Cesarean sections were performed on day 20 of gestation. In the pregnant rats, 2 of 13 and 2 of 12 dams died at 9.0 and 12.0 mg kg , respectively. Vaginal bleeding, bloody mouth and nose, somnolence and depression of body weight gain and food intake were observed at 9.0 and 12.0 mg kg at late stages of pregnancy. No statistically significant reductions in maternal thymus and spleen weights were observed on day 20 of gestation. Increase in embryonic and fetal deaths and in dams with total resorption of fetuses were observed at doses of more than 6.0 mg kg . The doses of TPTA in this experiment, however, induced no teratogenic effects in rats.

Effect of qualitative differences in dietary fat on dexfenfluramine mediated depression of food intake and serotonin metabolism

Previously, we showed that rats fed greater amounts of dietary saturated fat select more protein and less carbohydrate than rats fed diets with lesser amounts. Four experiments were designed to determine if dietary fat-induced differences in selection behavior were mediated by the serotonergic system. All diets were isoenergetic with 20% (w/w) fat. In experiment I, rats were fed diets (24% protein, 40% carbohydrate, 20% fat) containing 9%, 8%, or 3% saturated fat. Dexfenfluramine (0, 0.6 and 1.2 mg/kg) resulted in a dose-dependent decrease in food intake in all groups at 1, 2, and 16 hours after food presentation ( P<0.0006). In addition, there was a significant diet by drug interaction at each time interval ( P<0.05), indicating the effect was not independent of dietary fat composition. When rats selected from high-protein low-carbohydrate and low-protein high-carbohydrate diets containing 9% or 3% saturated fat (total fat content of all diets remained 20% (w/w)), dexfenfluramine resulted in decreased intake of food, protein, and carbohydrate in both groups ( P<0.05). However, there was no significant diet by drug interaction at any time interval. Consumption of the low-protein high-carbohydrate diet was decreased more than consumption from the high-protein low-carbohydrate diet regardless of diet fat treatment after 1 or 2 hours of feeding. Serotonin turnover was assessed in experiments 3 and 4 using pargyline to block monoamine oxidase. There was no dietary fat by treatment effect on hypothalamic indoleamines or tryptophan when rats were fed single diets with a fixed protein/carbohydrate ratio, or when rats consumed selection diets. Thus, turnover rates were similar across diet fat treatments. The results of these experiments suggest that qualitative differences in dietary fat composition may influence the anorectic response to dexfenfluramine when rats are fed single diets with fixed protein/carbohydrate ratios, but that changes in steady-state serotonin metabolism or in serotonin turnover are not involved in the mechanism.

Enhanced release of cholecystokinin in chickens fed diets high in phenylalanine or tyrosine

1. 1. Whether the ingestion of excess phenylalanine (Phe) or tyrosine (Tyr) in diets alters the release of cholecystokinin (CCK) into the blood was investigated in chickens. A single meal of control, Phe excess, or Tyr excess diets was given through a stomach tube, followed by the CCK determination with specific CCK-8 antibody. 2. 2. Plasma CCK level increased significantly at 30 min after feeding the diets: about 2.5 times the basal level in the control group and about 3 times the basal level in both of the experimental groups. 3. 3. The Phe excess diet significantly delayed crop emptying rates compared to the control diet, while the Tyr diet on the contrary enhanced the emptying rate. 4. 4. Enhanced plasma CCK levels and delayed crop emptying by Phe excess diet are suggested to be associated with depressed food intake.

Teratogenicity study of tri- n-butyltin acetate in rats by oral administration

A teratological test was carried out on tri- n-butyltin acetate (TBTA) used as a biocide and anti-fouling agent. Pregnant Wistar rats were treated orally with TBTA at dose levels of 0, 1, 2, 4, 8, and 16 mg/kg from days 7–17 of gestation. Cesarean sections were performed on day 20 of gestation. In pregnant rats, salivation and depression of body weight gain and food intake were observed at a late stage of pregnancy at the highest dose level of TBTA. Atrophy of the thymus was also observed in a dose-dependent manner on day 20 of gestation. In the fetuses, treatment with the highest dose level increased embryonic and fetal deaths, increased the incidence of fetuses with cleft palate, cervical rib and/or rudimentary lumbar rib, and decreased the body weights of fetuses.

Effects of continuous graded total parenteral nutrition on feeding indexes and metabolic concomitants in rats

The influence of graded amounts of total parenteral nutrition (TPN) on food intake and feeding indexes was investigated in 90 rats housed in Automated Computerized Rat Eater Meter metabolic cages with free access to water and chow. When food intake was stable after catheter placement, 10 control rats continued with the 3 ml/h normal saline used for catheter patency, whereas study rats were given graded TPN continuously for 3 days, amounting to the equivalent of 26% (TPN-26), 53% (TPN-53), 81% (TPN-81), or 114% (TPN-114) of their daily caloric needs. TPN consisted of glucose, fat, and amino acids in the caloric ratio of 50:30:20. In study rats, the graded TPN depressed food intake, meal number, meal size, and eventually food consumption rate, meal sniffs, and intermeal sniffs in a dose- and time-dependent manner. During graded TPN, rats decreased total food intake by eating fewer, smaller, shorter meals at a decreasing consumption rate; sniffing activities were correspondingly curtailed. Stopping TPN led to normalization of feeding indexes. Blood glucose did not change while plasma insulin rose with graded TPN. A decrease in hepatic glycogen and an increase in hepatic triglycerides occurred. Plasma valine, phenylalanine, and methionine rose in a TPN dose-dependent manner. TPN-26 and TPN-53 significantly decreased whole brain amino acids; with TPN-114 no change occurred. Brain influx of tryptophan remained unchanged, but a progressive decrease in brain influx of tyrosine occurred. Whole brain dopamine and serotonin were depressed with TPN-26 and TPN-81 but were normal with TPN-114.(ABSTRACT TRUNCATED AT 250 WORDS)

Opiatergic modulation of preparatory and consummatory components of feeding and drinking

We present data here indicating that stimulation of kappa but not mu opiate receptors influences motivational and consummatory aspects of feeding and drinking. To differentiate mu and kappa mechanisms controlling preparatory (appetitive) and consummatory components of ingestive behavior, the effects of morphine (MORPH), compound U50488H (U50) and naloxone (NAL) were studied in rats trained to negotiate a straight runway using food or water as reinforcer. At doses that increase feeding and drinking in conditions of free access to food and water (i.e., 1–2 mg/kg IP), MORPH affected neither food- nor water-maintained runway performance. Since 1 mg/kg of NAL is also devoid of effects, mu-opiate mechanisms are probably not involved in food- or water-maintained behavior. Pharmacological manipulation of kappa-opiate mechanisms had complex effects. At 5 mg/kg, NAL accelerated satiation, depressing food intake, without affecting running. U50 did not increase food intake, but accelerated running for food, an effect that was antagonized by a high dose of NAL (5 mg/kg). These findings suggest that motivational and consummatory components of food-maintained runway performance are both activated by kappa-opiate mechanisms. NAL also reduced water intake but had minimal influences on running. In contrast, U50 depressed both water intake and runway performance; rather than being antagonized, these effects were slightly enhanced by NAL. The combined antidipsic and diuretic effects of U50 suggest that kappa-opiate mechanisms play a dissipatory role in water balance. However, the similar antidipsic effects of U50 and NAL, and the fact that NAL did not antagonize the antidipsic effects of U50, suggest that U50 may reduce drinking by mechanisms other than kappa-opiate agonism.

Reduced selenium status in chicks given diets low in Sulphur‐containing amino acids and containing Sodium Nitroprusside as a source of cyanide

1. Two experiments were carried out to study the effect of dietary cyanide, given in the form of sodium nitroprusside (SNP), on the growth and selenium status of chicks fed on diets low in sulphur-containing amino acids. 2. In experiment 1, SNP (0.3 g/kg) depressed growth rate and food intake when included in diets low in total sulphur-containing amino acids. It also reduced plasma and liver glutathione peroxidase activity (GSH-Px) and kidney selenium concentration. These latter variables also showed increases in response to supplements of selenium of 0.1 and 0.2 mg selenium/kg (as sodium selenite) although growth was not affected. 3. In experiment 2, SNP did not affect growth when reduced to 0.1 g/kg in diets low both in methionine and total sulphur-containing amino acids. It did, however, reduce plasma GSH-Px activity, which again increased in response to similar dietary supplements of selenium. 4. It is concluded that dietary cyanide effectively increases the requirement for selenium and could induce deficiency in diets only marginally adequate in selenium, particularly when the supply of sulphur-containing amino acids was marginal or inadequate.

Serotonin3 receptor antagonists block anorectic responses to amino acid imbalance

The role of serotonin3 (5-HT3) receptors in the initial food intake depression of rats ingesting amino acid imbalanced or high-protein diets was investigated. The 5-HT antagonists metergoline, pirenpirone, ICS 205-930, and MDL 72222, the dopamine antagonist pimozide, or the alpha-adrenergic antagonist phentolamine were injected 15-45 min before presentation of test diets. Food intake was measured at intervals for 3 days. The 5-HT3 antagonists, ICS 205-930 and MDL 72222, restored feeding of a mild isoleucine (Ile)-imbalanced diet to control levels, although MDL 72222 had a longer time course of action. ICS 205-930 also increased intake of a severe Ile-imbalanced diet and Thr-imbalanced diet but not a high-protein (44% casein) diet. Treatment with metergoline, which blocks 5-HT1, 5-HT2, and dopamine receptor sites but not 5-HT3 sites, increased intake of the basal diet at 3 and 6 h but did not significantly alter intake of the mild Ile-imbalanced diet. Although pimozide tended to increase intake of the mild imbalanced diet, neither dopamine nor alpha-adrenergic receptor antagonism significantly affected imbalanced diet intake. Thus 5-HT3 receptors may mediate the anorexigenic activity of 5-HT associated with feeding an amino acid-imbalanced diet.

Factors affecting the voluntary intake of food by sheep

The site where osmotically active substances act to depress food intake was determined in sheep. After 5.5 h of food deprivation, solutions of sodium chloride or polyethylene glycol-200 (PEG-200) were added to either the reticulo-rumen or the abomasum. The sheep were then immediately offered pelleted lucerne (Medicago sativa). Water was withheld during the first 60 min of feeding but was available from 60 to 90 min. There was a linear inhibition in food intake in the first 10 min after loading 2.37, 6.25, 12.5, 25.0 or 50.0 g NaCl into the rumen according to a 5 x 5 Latin square design (P = 0.0001). The intake reduction was 3.49 g food/g NaCl. An osmotic load of PEG-200 equivalent to 50 g NaCl also significantly inhibited food intake in the first 10 min of the meal compared with a control treatment. The inhibition of food intake after loading 55 g NaCl into the rumen was not affected by injecting lidocaine hydrochloride into the reticulum immediately before NaCl loading. NaCl injected into the abomasum did not significantly affect food intake in the first 10 min of feeding even though the tonicity of abomasal digesta was increased to unphysiological levels. There was no consistent relationship between food intake and the change in the tonicity of jugular plasma following solute loading and drinking. The sensing site of hypertonicity was localized to the wall of the reticulo-rumen where neuronal receptors appear to be capable of detecting osmotic pressure within the physiological range to depress food intake. These receptors should be identified and characterized because of their possible significance in limiting food intake by ruminants.

Longevity Hormesis. A review

The phenomenon of longevity hormesis is reviewed. The life-prolonging effects of longevity hormesis are compared and contrasted with those resulting from depressed food intake. The use of age-specific mortality rate analysis as a tool to characterize the separate and distinct effects of longevity hormesis, cumulative toxicity and depressed food intake on the survival of laboratory animals is illustrated. Finally, model systems through which the mechanism(s) of longevity hormesis may be elucidated are discussed.

Growth and development of male and female rats treated with the Leydig cell cytotoxin ethane dimethane sulphonate during the suckling period

The growth inhibiting effects of the Leydig cell cytotoxin ethane dimethane sulphonate (EDS) were investigated after treatment of both male and female neonatal rats. Pups were injected daily from day 4 to day 15 of age with EDS (50 mg/kg body weight sc), vehicle or water, or were not injected, according to a within-litter control experimental design. The rats were killed for necropsy at 40 and 80 days. The timing of attainment of the developmental milestones that appear during the suckling period was unaffected by treatment, but vaginal opening was 2 days later in EDS-treated females. After a delay of 9–10 days after the start of treatment the growth in body weight of both male and female EDS-treated rats was substantially and progressively depressed, such that by 80 days male and female EDS-treated rats showed body-weight deficits of 18 and 25%, respectively. The food intake of EDS-treated rats at 10 wk of age was less than that of controls, but was appropriate or more than appropriate for metabolic body size. As expected, testes were vestigial in EDS-treated males and the accessory male sexual organs were very small. Ovary and uterus weights were appropriate for body weight in EDS-treated females. At 80 days, liver weight was high for body weight in EDS-treated rats of both sexes. Possible mechanisms for the effect on body growth are discussed. Depressed food intake is discounted. Endocrine involvement, perhaps some anomaly of growth hormone release, or a more generalized toxic effect seem more likely.

Dietary Branched-Chain Amino Acids and Protein Selection by Rats

Consumption by rats of high protein diets is associated with elevated plasma and brain concentrations of branched-chain amino acids (BCAA). We examined the possibility that changes in BCAA concentrations in blood and brain might serve as modulators of protein consumption. After young rats had adjusted to selecting between a 10% or 25% casein diet and a 50% casein diet, a mixture of BCAA was included in the diet containing the lower amount of protein (10% + BCAA, 25% + BCAA). Supplementation of the 10% or 25% casein diets with BCAA and subsequent elevation of BCAA concentrations in plasma and brain were associated with increased selection of protein in rats given the 10% + BCAA/50% casein diet choice, but not in rats offered the 25% + BCAA/50% casein diets. When no alternative diet was available, addition of BCAA to a 15% casein diet depressed food intake, and rats given a choice between a 15% casein diet with or without added BCAA selected almost exclusively the diet without added BCAA. Although BCAA concentrations were high in plasma and brain in all experiments, concentrations of methionine, tyrosine, phenylalanine, tryptophan and histidine were low in brain in experiments in which rats altered their diet or protein selection after BCAA addition. High concentrations of BCAA in plasma and brain were not consistently associated with changes in protein selection.