Characteristics of thyroid function in experimental protein malnutrition

Brown adipose tissue: can it keep us slim? A discussion of the evidence for and against the existence of diet-induced thermogenesis in mice and men

The issue under discussion here is whether a decrease in the degree of UCP1 activity (and brown adipose tissue activity in general) could be a cause of obesity in humans. This possibility principally requires the existence of the phenomenon of diet-induced thermogenesis. Obesity could be a consequence of a reduced functionality of diet-induced thermogenesis. Experiments in mice indicate that diet-induced thermogenesis exists and is dependent on the presence of UCP1 and thus of brown adipose tissue activity. Accordingly, many (but not all) experiments indicate that in the absence of UCP1, mice become obese. Whether similar mechanisms exist in humans is still unknown. A series of studies have indicated a correlation between obesity and low brown adipose tissue activity, but it may be so that the obesity itself may influence the estimates of brown adipose tissue activity (generally glucose uptake), partly explaining the relationship. Estimates of brown adipose tissue catabolizing activity would seem to indicate that it may possess a capacity sufficient to help maintain body weight, and obesity would thus be aggravated in its absence. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part II)'.

Effects of disease on foraging behaviour and success in an individual free-ranging northern elephant seal

Evaluating consequences of stressors on vital rates in marine mammals is of considerable interest to scientific and regulatory bodies. Many of these species face numerous anthropogenic and environmental disturbances. Despite its importance as a critical form of mortality, little is known about disease progression in air-breathing marine megafauna at sea. We examined the movement, diving, foraging behaviour and physiological state of an adult female northern elephant seal (Mirounga angustirostris) who suffered from an infection while at sea. Comparing her to healthy individuals, we identified abnormal behavioural patterns from high-resolution biologging instruments that are likely indicators of diseased and deteriorating condition. We observed continuous extended (3-30 minutes) surface intervals coinciding with almost no foraging attempts (jaw motion) during 2 weeks of acute illness early in her post-breeding foraging trip. Elephant seals typically spend ~ 2 minutes at the surface. There were less frequent but highly extended (30-200 minutes) surface periods across the remainder of the trip. Dive duration declined throughout the trip rather than increasing. This seal returned in the poorest body condition recorded for an adult female elephant seal (18.3% adipose tissue; post-breeding trip average is 30.4%). She was immunocompromised at the end of her foraging trip and has not been seen since that moulting season. The timing and severity of the illness, which began during the end of the energy-intensive lactation fast, forced this animal over a tipping point from which she could not recover. Additional physiological constraints to foraging, including thermoregulation and oxygen consumption, likely exacerbated her already poor condition. These findings improve our understanding of illness in free-ranging air-breathing marine megafauna, demonstrate the vulnerability of individuals at critical points in their life history, highlight the importance of considering individual health when interpreting biologging data and could help differentiate between malnutrition and other causes of at-sea mortality from transmitted data.

Adverse perinatal conditions and the developmental origins of thyroid dysfunction-Lessons from Animal Models

PURPOSE

Nutritional, hormonal, and environmental status during development can predispose the individual to obesity and endocrine diseases later in life, an association known as metabolic programming. In general, weight loss or gain are seen in thyroid disorders, and thyroid function can be affected by body adiposity. In addition, hyper- and hypothyroidism can be related to metabolic programming. Our aim was to gather evidence that regardless of the type or critical window of metabolic imprinting, offspring exposed to certain adverse perinatal conditions have a higher risk of developing thyroid dysfunction.

METHODS

We reviewed literature data that relate insults occurring during pregnancy and/or lactation to short- and long-term offspring thyroid dysfunction in animal models.

RESULTS

Few studies have addressed the hypothalamic-pituitary-thyroid axis and thyroid dysfunction related to metabolic programming. The literature shows that under- and overnutrition, exposure to endocrine disruptors, early weaning, maternal thyroid disease and maternal high-fat diet can induce alterations in offspring thyroid function in a sex-dependent manner.

CONCLUSION

Based on the few available data, mainly in rodent models, we can conclude that diet, hormones, and environmental contaminants are related to the developmental origins of later thyroid dysfunction by interrupting the normal maturation of the thyroid gland.

Multiomics assessment of dietary protein titration reveals altered hepatic glucose utilization

Dietary protein restriction (PR) has rapid effects on metabolism including improved glucose and lipid homeostasis, via multiple mechanisms. Here, we investigate responses of fecal microbiome, hepatic transcriptome, and hepatic metabolome to six diets with protein from 18% to 0% of energy in mice. PR alters fecal microbial composition, but metabolic effects are not transferable via fecal transplantation. Hepatic transcriptome and metabolome are significantly altered in diets with lower than 10% energy from protein. Changes upon PR correlate with calorie restriction but with a larger magnitude and specific changes in amino acid (AA) metabolism. PR increases steady-state aspartate, serine, and glutamate and decreases glucose and gluconeogenic intermediates. ¹³C6 glucose and glycerol tracing reveal increased fractional enrichment in aspartate, serine, and glutamate. Changes remain intact in hepatic ATF4 knockout mice. Together, this demonstrates an ATF4-independent shift in gluconeogenic substrate utilization toward specific AAs, with compensation from glycerol to promote a protein-sparing response.

Branched-chain Amino Acids: Catabolism in Skeletal Muscle and Implications for Muscle and Whole-body Metabolism

Branched-chain amino acids (BCAAs) are critical for skeletal muscle and whole-body anabolism and energy homeostasis. They also serve as signaling molecules, for example, being able to activate mammalian/mechanistic target of rapamycin complex 1 (mTORC1). This has implication for macronutrient metabolism. However, elevated circulating levels of BCAAs and of their ketoacids as well as impaired catabolism of these amino acids (AAs) are implicated in the development of insulin resistance and its sequelae, including type 2 diabetes, cardiovascular disease, and of some cancers, although other studies indicate supplements of these AAs may help in the management of some chronic diseases. Here, we first reviewed the catabolism of these AAs especially in skeletal muscle as this tissue contributes the most to whole body disposal of the BCAA. We then reviewed emerging mechanisms of control of enzymes involved in regulating BCAA catabolism. Such mechanisms include regulation of their abundance by microRNA and by post translational modifications such as phosphorylation, acetylation, and ubiquitination. We also reviewed implications of impaired metabolism of BCAA for muscle and whole-body metabolism. We comment on outstanding questions in the regulation of catabolism of these AAs, including regulation of the abundance and post-transcriptional/post-translational modification of enzymes that regulate BCAA catabolism, as well the impact of circadian rhythm, age and mTORC1 on these enzymes. Answers to such questions may facilitate emergence of treatment/management options that can help patients suffering from chronic diseases linked to impaired metabolism of the BCAAs.

Fluoride-induced thyroid dysfunction in rats: roles of dietary protein and calcium level

To assess the roles of dietary protein (Pr) and calcium (Ca) level associated with excessive fluoride (F) intake and the impact of dietary Pr, Ca, and F on thyroid function, 144 30-day-old Wistar albino rats were randomly allotted to six groups of 24 (female:male = 1:1). The six groups were fed (1) a normal control (NC) diet (17.92% Pr, 0.85% Ca = NC group); (2) the NC diet and high F (338 mg NaF [=150 mg F ion]/L in their drinking water = NC+F group); (3) low Pr and low Ca diet (10.01% Pr, 0.24% Ca = LPrLCa group); (4) low Pr and low Ca diet plus high F = LPrLCa+F group; (5) high Pr and low Ca diet plus high F (25.52% Pr, 0.25% Ca = HPrLCa+F group); and (6) low Pr and high Ca diet plus high F (10.60% Pr, 1.93% Ca = LPrHCa+F group). The areas of thyroid follicles were determined by Image-Proplus 5.1, and triiodothyronine (T3), free T3 (FT3), thyroxine (T4), and free T4 (FT4) levels in serum were measured by radioimmunoassay. The histopathological study revealed obviously flatted follicular epithelia cells and hyperplastic nodules, consisting of thyroid parafollicular cells that appeared by excessive F ingestion, on the 120th day. Pr or Ca supplementation reverses the F-induced damage in malnutrition. The serum T3, FT3, T4, and FT4 levels in the NC+F group were significantly decreased and significantly increased in the LPrLCa+F group. Thus, excessive F administration induces thyroid dysfunction in rats; dietary Pr and Ca level play key roles in F-induced thyroid dysfunction.

Dietary protein modulates circadian changes in core body temperature and metabolic rate in rats

We assessed the contribution of dietary protein to circadian changes in core body temperature (Tb) and metabolic rate in freely moving rats. Daily changes in rat intraperitoneal temperature, locomotor activity (LMA), whole-body oxygen consumption (VO2), and carbon dioxide production (VCO2) were measured before and during 4 days of consuming a 20% protein diet (20% P), a protein-free diet (0% P), or a pair-fed 20% P diet (20% P-R). Changes in Tb did not significantly differ between the 20% P and 20% P-R groups throughout the study. The Tb in the 0% P group remained elevated during the dark (D) phase throughout the study, but VO2, VCO2, and LMA increased late in the study when compared with the 20% P-R group almost in accordance with elevated Tb. By contrast, during the light (L) phase in the 0% P group, Tb became elevated early in the study and thereafter declined with a tendency to accompany significantly lower VO2 and VCO2 when compared with the 20% P group, but not the 20% P-R group. The respiratory quotient (RQ) in the 0% P group declined throughout the D phase and during the early L phase. By contrast, RQ in the 20% P-R group consistently decreased from the late D phase to the end of the L phase. Our findings suggest that dietary protein contributes to the maintenance of daily oscillations in Tb with modulating metabolic rates during the D phase. However, the underlying mechanisms of Tb control during the L phase remain obscure.

Serum leptin and insulin levels in lactating protein-restricted rats: implications for energy balance

The present study analysed the effect of protein restriction on serum insulin and leptin levels and their relationship with energy balance during lactation. Four groups of rats received isocaloric diets containing 170 g protein/kg or 60 g protein/kg from pregnancy until the 14th day of lactation: control non-lactating, control lactating (both fed a control diet), low-protein non-lactating and low-protein lactating. Energy intake, body composition, energy balance, serum insulin and leptin concentrations and the relationship between these hormones and several factors related to obesity were analysed. Low-protein-intake lactating rats exhibited hypoinsulinaemia, hyperleptinaemia, hypophagia and decreased energy expenditure compared with control lactating rats. The protein level in the carcasses was lower in the low-protein lactating group than in the control lactating group, resulting in a higher fat content in the first group compared with the latter. Body fat correlated inversely with serum insulin and positively with serum leptin level. There was a significant negative correlation between serum leptin and energy intake, and a positive relationship between energy intake and serum insulin level in lactating rats and in the combined data from both groups. Energy expenditure was correlated positively with serum insulin and negatively with serum leptin in lactating rats and when data from control non-lactating and lactating rats were pooled. Lactating rats submitted to protein restriction, compared with lactating control rats, showed that maternal reserves were preserved owing to less severe negative energy balance. This metabolic adaptation was obtained, at least in part, by the hypoinsulinaemia that resulted in increased insulin sensitivity favouring enhanced fat deposition, hyperleptinaemia and hypophagia.

Effects of lysine deficiencies on plasma levels of thyroid hormones, insulin-like growth factors I and II, liver and body weights, and feed intake in growing chickens

Adequate (1.10%) and deficient (0.88, 0.66, and 0.53%) levels of Lys were fed to broiler chicks from 9 to 23 d of age. Groups fed the control diet (1.10% Lys) were also pair-fed daily with each deficient group. Compared with the free-fed control, graded decreases in feed intake occurred as the deficiency worsened, and these were significantly different with 0.66 and 0.53% Lys. Growth decreased significantly with each deficient level of Lys compared with the free-fed control and was always significantly lower than in the pair-fed control groups in each set. Plasma triiodothyronine (T3) was elevated in chicks fed 0.88 and 0.66% lysine but not with 0.53% when compared with the full-fed control treatment. However, in deficient chicks receiving 0.66 and 0.53% Lys, T3 levels were significantly higher compared with their pair-fed controls. Plasma T4 was not significantly different between any treatments. Liver weights decreased significantly at each level of Lys deficiency, but most of the differences disappeared when expressed relative to body weight. Plasma insulin-like growth factor (IGF)-I decreased significantly with the most severe Lys deficiency. However, it decreased to a similar degree in the pair-fed controls, showing that this effect was primarily due to the lower feed intake. Plasma IGF-II levels did not differ between any treatments. No correlations were evident between thyroid hormones and IGF-I or IGF-II values. We concluded that the primary effect of Lys deficiency was an elevation in plasma T3 levels without accompanying changes in plasma T4. No effect of the Lys deficiency per se on plasma IGF-I and IGF-II and liver weights relative to body weights was found.

Effects of methionine deficiencies on plasma levels of thyroid hormones, insulin-like growth factors-I and -II, liver and body weights, and feed intake in growing chickens

We showed previously that Met deficiency at 0.25% of the diet causes elevations in plasma triiodothyronine (T3) in broilers. In the present study, plasma levels of thyroid hormones as well as insulin-like growth factors (IGF)-I and -II were measured in chicks fed 3 deficient levels of total Met. Control (0.5%) and Met-deficient diets (0.4, 0.3, and 0.2%) were fed to male broilers from 8 to 22 d of age. Additional groups of control chicks were pair-fed with the Met-deficient ones. Chicks receiving 0.4% Met increased feed intake by 10% with no significant change in body weight. The more severe Met deficiencies of 0.3 and 0.2% caused graded reductions in feed intake and weight gain. However, corresponding pair-fed control chicks were significantly heavier. These changes suggest more marked alterations in metabolic processes with 0.3 and 0.2% Met than with 0.4% Met. Liver weights were heavier in chicks fed 0.3 and 0.2% Met but not 0.4%. Plasma T3 was higher in all deficient chicks compared with the free-fed control, which was significant only with 0.3% Met. However, with 0.3 and 0.2% Met, plasma T3 was significantly elevated compared to pair-fed controls. Plasma thyroxine (T4) was lower in all deficient groups, which was significant only with 0.2% Met, whereas no significant differences occurred between deficient chicks and their pair-fed controls. Plasma IGF-I levels were not significantly different, but they were consistently lower in deficient chicks and deserve further study. Plasma IGF-II was significantly less in chicks fed 0.2% Met compared to pair-fed controls suggesting that Met deficiency interferes with IGF-II metabolism. We concluded that a deficit of dietary Met altered plasma T3 and IGF-II levels, but the effect was dependent on the degree of deficiency.

Changes in UCP expression in tissues of Zucker rats fed diets with different protein content

The effect of dietary protein content on the uncoupling proteins (UCP) 1, 2 and 3 expression in a number of tissues of Zucker lean and obese rats was studied. Thirty-day-old male Zucker lean (Fa/?) and obese (fa/fa) rats were fed on hyperproteic (HP, 30% protein), standard (RD, 17% protein) or hypoproteic (LP, 9% protein) diets ad libitum for 30 days. Although dietary protein intake affected the weights of individual muscles in lean and obese animals, these weights were similar. In contrast, huge differences were observed in brown adipose tissue (BAT) and liver weights. Lean rats fed on the LP diet generally increased UCP expression, whereas the HP group had lower values. Obese animals, HP and LP groups showed higher UCP expression in muscles, with slight differences in BAT and lower values for UCP3 in subcutaneous adipose tissue. The mean values of UCP expression in BAT of obese rats were lower than in their lean counterpart, whereas the expression in skeletal muscle was increased. Thus, expression of UCPs can be modified by dietary protein content, in lean and obese rats. A possible thermogenic function of UCP3 in muscle and WAT in obese rats must be taken into account.

Hepatothermic therapy of obesity: rationale and an inventory of resources

Hepatothermic therapy (HT) of obesity is rooted in the observation that the liver has substantial capacities for both fatty acid oxidation and for thermogenesis. When hepatic fatty acid oxidation is optimized, the newly available free energy may be able to drive hepatic thermogenesis, such that respiratory quotient declines while basal metabolic rate increases, a circumstance evidently favorable for fat loss. Effective implementation of HT may require activation of carnitine palmitoyl transferase-1 (rate-limiting for fatty acid beta-oxidation), an increase in mitochondrial oxaloacetate production (required for optimal Krebs cycle activity), and up-regulation of hepatic thermogenic pathways. The possible utility of various natural agents and drugs for achieving these objectives is discussed. Potential components of HT regimens include EPA-rich fish oil, sesamin, hydroxycitrate, pantethine, L-carnitine, pyruvate, aspartate, chromium, coenzyme Q10, green tea polyphenols, conjugated linoleic acids, DHEA derivatives, cilostazol, diazoxide, and fibrate drugs. Aerobic exercise training and very-low-fat, low-glycemic-index, high-protein or vegan food choices may help to establish the hormonal environment conducive to effective HT. High-dose biotin and/or metformin may help to prevent an excessive increase in hepatic glucose output. Since many of the agents contemplated as components of HT regimens are nutritional or food-derived compounds likely to be health protective, HT is envisioned as an on-going lifestyle rather than as a temporary 'quick fix'. Initial clinical efforts to evaluate the potential of HT are now in progress.

Regulation of branched-chain alpha-keto acid dehydrogenase kinase expression in rat liver

Branched-chain amino acids are toxic in excess but have to be conserved for protein synthesis. This is accomplished in large part by control of the activity of the branched-chain alpha-keto acid dehydrogenase complex by phosphorylation/dephosphorylation. Regulation of the activity of the hepatic enzyme appears particularly important, at least in rats, since an exceptional high activity of the complex in this tissue makes the liver the primary clearing house for excess branched-chain alpha-keto acids released by other tissues. The degree to which the branched-chain alpha-keto acid dehydrogenase complex is inactivated by phosphorylation is determined by the activity of the branched-chain alpha-keto acid dehydrogenase kinase, which is itself regulated by allosteric effectors as well as factors that affect its level of expression. Well established among these are the alpha-keto acid produced by leucine transamination, which is a potent inhibitor of the kinase, and starvation for dietary protein, which causes increased expression of the branched-chain alpha-keto acid dehydrogenase kinase. The latter finding resulted in the working hypothesis that nutrients and hormones regulate expression of the branched-chain alpha-keto acid dehydrogenase kinase. Evidence has been obtained for the involvement of thyroid hormone, glucocorticoids and ligands for peroxisome proliferator-activated receptor alpha. Thyroid hormone induces, whereas glucocorticoids and peroxisome proliferator-activated receptor alpha ligands repress, expression of the kinase. Increased blood levels of thyroid hormone are proposed to be responsible for increased expression of branched-chain alpha-keto acid dehydrogenase kinase in animals starved for protein.

Hepatic monitoring of essential amino acid availability may regulate IGF-I activity, thermogenesis, and fatty acid oxidation/synthesis

Diets that are low in certain essential amino acids (EAAs), whether owing to low protein content or poor protein quality, tend to down-regulate systemic IGF-I activity, boost thermogenesis, and suppress hepatic capacity for lipogenesis, while promoting hepatic fatty acid oxidation. It is proposed that for each EAA there is a regulatory protein in hepatocytes whose activity is repressed by adequate levels of its EAA; if one (or more) of these regulatory proteins is active, it serves as a signal of EAA deficiency which then mediates the aforementioned effects on IGF-I activity, thermogenesis, and hepatic fatty acid metabolism. Mechanisms which monitor EAA availability likewise play a role in appetite regulation, thus accounting for the fact that spontaneous calorie consumption tends to be lower on high-protein diets. Diets low in protein quantity or quality may decrease insulin secretion, an effect which should contribute to their impact on IGF-I activity and lipid metabolism. The fact that vegans ingest diets that tend to be relatively low in certain EAAs may play a key role in their characteristic leanness and their decreased risk for diabetes, coronary disease, and cancer.

Low-protein diet changes thyroid function in lactating rats

Lactating rats were fed with free access to an 8% protein-restricted diet (PR); the control group was fed a 23% protein diet (C). An energy-restricted (pair-fed) group was given the same food as the animals in the control group, but the amounts of food consumed by both PF and PR were about the same. The body weight and serum albumin concentration of PR and PF dams were significantly (P < 0. 05) lower than that of the controls. The PR group had a significant increase in serum-free triiodothyronine (FT3) concentration, 24-hr mammary gland and milk radioiodine (I131) uptake (67%, 278%, and 200%, respectively) as compared with the controls. On the other hand, those animals had a significantly lower serum-free thyroxine (FT4) concentration and 2- and 24-hr thyroid I131 uptake (67%, 64%, and 74%, respectively). Protein malnutrition during lactation did not alter thyroid or liver 5'-deiodinase activity significantly. However, PF dams had a significantly lower (25%) thyroid 5'-deiodinase activity. These data suggest that protein-restricted lactating dams had an adaptive change in the thyroid function, which could be important to increase the transference of iodine or triiodothyronine through the milk to their pups and prevent sequelae of neonatal hypothyroidism.

Energy metabolism and thyroid hormone levels of growing rats in response to different dietary proteins--soy protein or casein

Energy balances were measured by indirect calorimetry in four experiments on male growing rats, fed restrictively on isoenergetic and isonitrogenous (10% CP) diets based on either casein supplemented with methionine, or soy protein isolate (experiments 1, 2 and 3) and soy protein isolate supplemented with methionine (experiment 0), respectively. At the end of experiments the rats were killed for body analysis and determination of thyroid hormones and lipids in blood as well as mitochondrial respiration in liver and heart. Feeding of non-supplemented soy protein resulted in a lower efficiency of energy utilisation as well as a lower protein utilisation compared to casein-fed and supplemented soy protein-fed rats. Chemical body composition was not markedly different between the dietary groups. After long-term feeding of soy protein (experiment 3) mass and mitochondrial protein content of the interscapular brown adipose tissue were increased compared to casein-fed rats. Serum thyroid hormone levels were not changed (T3 and free T3) or were significantly lowered (T4 and free T4) following soy protein feeding in comparison with casein feeding (except for experiment 2). Cholesterol and triglycerides were decreased on an average in response to soy protein or supplemented soy protein feeding. In two of three experiments a significant lower efficiency of hepatic mitochondrial respiration with succinate as substrate, expressed by the ratio of added ADP to oxygen consumed, was observed in soy protein-fed rats compared to casein-fed rats.

Dietary protein does not affect overloaded skeletal muscle in rats

We compared the effects of three levels of dietary protein, i.e., 7% (low protein; LP); 17.5% (adequate protein; CON); or 30% (high protein; HP) on growth of functionally overloaded muscle in Sprague-Dawley male rats. Growth of plantaris and soleus muscles was induced by the surgical removal of gastrocnemius muscles in one hindlimb; muscles in the other leg were used as sham-operated, intra-animal controls. After 4 wk, rats fed the 7% LP diet gained less weight (-29%) and had lighter livers (-20%) and kidneys (-16%) than rats fed the CON diet (P < 0.05). Measurements of rats fed the 30% HP diet were not different from those of CON rats except that their kidneys were larger (+6%) (P < 0.05). The level of dietary protein did not affect the experimentally induced muscular growth in either plantaris or soleus muscles. Gains in overloaded plantaris muscles over sham-operated muscles were not different among rats fed LP, CON and HP diets for muscle mass (+42 to +45%), total protein (+42 to +46%) and myofibrillar protein (+40 to +44%). Soleus muscles also did not differ among diet groups for gains in mass (+20 to +33%), total protein (+20 to +33%) and myofibrillar protein (+21 to +33%). No dietary protein effects were found on myosin heavy chain isoform (I, IIa, IIx, IIb) expression in either plantaris or soleus muscles. We conclude that gains in plantaris and soleus muscle mass, total protein and myofibrillar protein induced by functional overload are not affected by low (7%) or high (30%) protein feeding in young male rats for 4 wk.

Lowering of plasma triiodothyronine level and sympathetic activity does not alter hypoalbuminaemia in rats fed on a diet of low protein concentration

Previous studies have described high plasma triiodothyronine (T3) concentrations and sympathetic activity in rats fed on low-protein diets. The present investigation examined how the nutritional status of rats fed on a low-protein diet was affected when these hormonal changes were reduced by drug administration. The low-protein diet (LP group) prevented growth, reduced plasma albumin levels, elevated plasma T3 concentration, and increased both the weight of the interscapular brown adipose tissue (BAT) and the activity of BAT cytochrome c oxidase (EC 1.9.3.1). Lowering the plasma T3 concentration (with carbimazole; CA group) elevated the plasma insulin concentration, promoted a small increase in the plasma albumin concentration and caused weight gain in comparison with the LP group. Reduction of sympathetic activity (with alpha-methyl-p-tyrosine; MT group) promoted a small elevation in plasma albumin concentration accompanied by a diminished T3 concentration, BAT weight, and an increase in fat deposition in relation to LP rats. In a second experiment, simultaneous lowering of the plasma T3 concentration and sympathetic activity (CA/MT group) resulted in weight gain associated with elevated plasma insulin concentration and fat deposition and a marked reduction in BAT cytochrome c oxidase activity. However no change in the hypoalbuminaemia was observed. The results of the present study suggest that in spite of the previously described increase in metabolic rate in fed on a diet with low-protein concentration when compared with controls, the mechanisms involved in the control of BAT activity and fat deposition seem to be independent of those which cause liver protein depletion and hypoalbuminaemia.

Growth and plasma thyroid hormone concentrations of chicks fed diets deficient in essential amino acids

Consumption of low protein (10%) diets is known to produce elevations in plasma triiodothyronine (T3) in growing chickens. Therefore, we evaluated the effect of individual essential amino acid deficiencies on plasma thyroid hormone concentrations. For 13 to 15 d, chicks were fed either a control diet free-choice, one of six amino acid-deficient diets free-choice, or the control diet, pair-fed at the level consumed by chicks fed each of the deficient diets. The control diet was a 50/50 mixture of broiler starter and purified amino acid diets. The amino acids, fed at the indicated percentages of National Research Council recommendations, were: arginine, 60%; lysine, 60%; threonine, 60%; leucine, 75%; isoleucine, 75%; and methionine, 50%. Feed consumption and weight gain were significantly lower in all deficient groups than in the free-choice control group. In all cases except leucine, deficient chicks also gained less weight than their pair-fed controls. Plasma T3 levels in the groups deficient in arginine, lysine, isoleucine, or methionine were higher than in their respective pair-fed controls. However, only with the isoleucine deficiency did T3 levels exceed those of control chicks given free access to feed. Thyroxine levels were significantly lower than control levels only with the lysine deficiency. These results suggest that changes in circulating levels of thyroid hormones in a protein deficiency may be a consequence of selected amino acid deficits, because individual essential amino acids, when deficient in the diet, do not exert the same effect on circulating levels of thyroid hormones.

Effect of a low protein diet on the energy metabolism of growing chickens

Two slaughter experiments were carried out to determine whether the protein content of the diet has an influence upon the efficiency of utilization of ME in fast growing chickens. A normal-protein diet (NPD, 204 g CP/kg DM: 14.7 MJ ME/kg DM) based on soybean meal as the sole source of protein was given at four different levels of intake (ad libitum or restricted at about 90, 65 and 40% ad lib) to 10-d-old animals for 2 weeks. In a parallel experiment the chickens were fed ad libitum a low protein diet (LPD, 66 g CP/kg DM: 15.0 MJ ME/kg DM) based on soybean meal. The intake of metabolizable energy ranged from 1675 to 777 and 1770 to 832 kJ/kgW0.75 per day for NPD and LPD treatments, respectively. Mean values of energy retention, gross efficiency of energy utilization and energy retained as protein were significantly (P < .05) lower and heat production (expressed as both kJ/kgW0.75 per day and kJ/kg body protein content0.75 per day) was significantly higher (P < .05) for the chickens fed on LPD. These findings support the concept of dietary-induced thermogenesis in response to reductions in dietary protein concentration. It is concluded that the increased heat production found in the birds fed on the low-protein diet can be explained by both an increase in energy requirements for maintenance (MEm) and a sharp decrease in the efficiency of utilization of ME of growth (k(g)).

Functional consequences of sustained sleep deprivation in the rat

Sleep deprivation disrupts vital biological processes that are necessary for cognitive ability and physical health, but the physiological changes that underlie these outward effects are largely unknown. The purpose of the present studies in the laboratory rat is to prolong sleep deprivation to delineate the pathophysiology and to determine its mediation. In the rat, the course of prolonged sleep deprivation has a syndromic nature and eventuates in a life-threatening state. An early and central symptom of sleep deprivation is a progressive increase in peripheral energy expenditure to nearly double normal levels. An attempt to alleviate this negative energy balance by feeding rats a balanced diet that is high in its efficiency of utilization prolongs survival and attenuates or delays development of malnutrition-like symptoms, indicating that several symptoms can be manipulated to some extent by energy and nutrient consumption. Most changes in neuroendocrine parameters appear to be responses to metabolic demands, such as increased plasma catecholamines indicating sympathetic activation. Plasma total thyroid hormones, however, decline to severely low levels; a metabolic complication that is associated with other sleep deprivation-induced symptoms, such as a decline in body temperature to hypothermic levels despite increased energy expenditure. Metabolic mapping of the brain revealed a dissociation between the energy metabolism of the brain and that of the body. Sleep deprivation's effects on cerebral structures are heterogeneous and unidirectional toward decreased functional activity. The hypometabolic brain structures are concentrated in the hypothalamus, thalamus and limbic systems, whereas few regions in the rest of the brain and none in the medulla, are affected. Correspondence can be found between some of the affected cerebral structures and several of the peripheral symptoms, such as hyperphagia and possible heat retention problems. The factor predisposing to mortality is a decreased resistance to infection. Lethal opportunistic organisms are permitted to infect the bloodstream, which presumably results in a cascade of toxic-like reactions. Host defense is thus the first system to fail. There is neither fever nor marked tissue inflammatory reactions typical of infectious disease states, suggesting that sleep deprivation is immunosuppressive. Each of the four abnormalities identified--(1) a deep negative energy balance and associated malnutrition; (2) heterogeneous decreases in cerebral function; (3) low thyroid hormone concentrations; and (4) decrease resistance to infection--can be viewed as having an early origin during the sleep deprivation process to signify the foremost pathogenic situation to which the other abnormalities might be secondarily related.(ABSTRACT TRUNCATED AT 400 WORDS)

Body dimensions and thyroid hormone levels in premenopausal and postmenopausal women from Austria

Correlations between thyroid hormone levels and body dimensions were investigated in a group of 124 premenopausal (ages 16-40 years) and 142 postmenopausal (ages 38-61 years) women from Vienna, Austria. Twenty-nine absolute body dimensions and thirteen anthropometric indices were correlated with the serum levels of thyroxine, triiodothyronine, thyroid-stimulating hormone, and thyroid-hormone-binding globulin as well as three hormone ratios (T3/T4, T4/TSH, T3/TSH). All hormones exhibited statistically significant correlations with 24 anthropometric variables and 11 indices. The correlations between thyroxine and triiodothyronine levels and the body measurements were predominantly positive in both proband groups. Higher thyroid hormone levels were associated positively with body dimensions, especially with the amount of subcutaneous fat tissue, in adult females independently of their menstrual status. The direction of the correlations between thyroid-stimulating hormone and body measures as well as anthropometric indices differed between the premenopausal and the postmenopausal women. While in premenopausal women mainly positive correlations between anthropometric characters and the level of thyroid stimulating hormone occur, in postmenopausal women most of these correlations are negative. This is probably due to the decrease of thyroid-stimulating hormone levels with increasing age, as well as with changes in body shape during the climacteric and after the menopause.

The effect of dietary protein on thyrotropin-releasing hormone and thyrotropin gene expression

In the rat, 48 h of food deprivation significantly reduces hypothalamic paraventricular nucleus (PVN) thyrotropin-releasing hormone (TRH) gene expression, anterior pituitary thyrotropin (TSH) gene expression and circulating triiodothyronine (T3). Using in situ hybridization histochemistry, we have now assessed the effect of selective nutritional deprivation, by comparing protein-free and protein and fat-free diets with a normal diet matched for total energy content. As previously demonstrated, fasting markedly reduced PVN TRH transcripts, pituitary TSB beta transcripts, circulating T3 and body weight. Compared to rats fed a control diet, rats fed a protein-free or a protein and fat-free diet of similar energy content showed a highly significant decrease in PVN TRH transcripts, pituitary TSB beta transcripts and circulating T3 levels. The exclusion of fat from the protein-free diet did not produce any further decline in the parameters measured. This indicates that variations in the protein composition alone of the diet are sufficient to reduce hypothalamic TRH mRNA, pituitary TSB beta mRNA and plasma T3, and are the predominant factors in the TRH response to starvation.

Quantitative morphological analysis of the pituitary gland in protein-calorie malnourished rats

A quantitative analysis of the pituitary gland was conducted to ascertain the effects of protein-calorie malnutrition on the morphology of the somatotrophs, gonadotrophs, thyrotrophs, and corticotrophs. Male rats were fed a low, 8% protein diet from 20 to 50 days of age, while their age-matched controls were given a diet containing 27% protein. The hypophyses were then processed for light microscopic immunocytochemical staining using antibodies to growth hormone, the beta subunits of luteinizing hormone and thyroid stimulating hormone, and adrenal corticotrophic hormone. The number of each cell type along with an evaluation of the cell, cytoplasmic, and nuclear areas was conducted using a computerized image analyzer. All of these parameters were reduced significantly in the somatotrophs as a result of the low protein diet, while in the gonadotrophs, the cell, cytoplasmic, and nuclear areas were similarly affected. Smaller cell number, cell area, and nuclear area were noted in the corticotrophs of the malnourished animals, while in the thyrotrophs, only the cell and nuclear areas were reduced. The data demonstrate that each pituitary cell type responds in a unique manner to undernutrition.

Metabolic changes during early starvation in rats fed a low-protein diet in the postweaning growth period

Metabolic changes during the first 24 hours of starvation were studied in rats previously adapted for 3 weeks during the postweaning growth period to a low-protein diet using lactalbumin as a dietary protein source. Previous adaptation to a high-quality, low-protein diet reduced the effects of early starvation on the loss of body and liver weight. In rats fed a low-protein diet (6% lactalbumin, LP rats), free triiodothyronine (T3) concentration remained higher than in control rats (13% lactalbumin, C rats) throughout the experiment (+38%, 24 hours), and the plasma insulin concentration, which was lower than in C rats during the first 6 hours (-56%), was not different thereafter. Plasma insulin to glucagon molar ratio was lower (-54%) and liver cyclic adenosine monophosphate (cAMP) concentration was higher (+28%) in LP than in C rats in the fed state, but these were not different at 24 hours of starvation. Plasma glucose concentration was slightly lower in LP than in C rats (-15%) in the fed state, but it was not different in both groups during starvation. Whereas they were unchanged in the fed state, plasma lactate concentration was lower (-57%) and free fatty acid and total ketone body concentrations were higher (+38% and +183%, respectively) in LP than in C rats at 24 hours of starvation.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermogenesis, low-protein diets, and decreased development of AFB1-induced preneoplastic foci in rat liver

The development of hepatocellular, putatively preneoplastic, gamma-glutamyl transpeptidase positive (GGT+) foci and tumors induced by aflatoxin B1 (AFB1) has been shown to be reduced in male F344 rats fed a diet containing 6% protein (as casein). This reduction occurs despite increased energy intake, when compared with animals fed a diet containing 22% protein. Among its many effects, low protein intake is known to increase the proportion of energy intake expended in the form of heat (thermogenesis); thus, this investigation examined the association between the development of GGT+ foci and alterations in indices of thermogenesis induced by feeding varying levels of dietary protein. Five days following the completion of AFB1 dosing, animals were assigned to groups fed 4%, 8%, 12%, 16%, or 22% dietary protein for 6 weeks. Foci development (% liver volume occupied) was markedly reduced in animals fed the low-protein diet (4%, 8%), yet calorie consumption per 100 g body wt was greater. A modest negative linear trend was observed in oxygen consumption with increasing levels of dietary protein intake. Urinary norepinephrine levels were elevated in the groups fed 4% and 8% protein; urinary dopamine and norepinephrine turnover rates in brown adipose tissue were highest in animals fed 4% protein. These results suggest that GGT+ foci development occurs when a "critical level" (approx 12%) of dietary protein intake is reached. Inhibition of foci development at lower levels of protein intake is associated with several indicators of increased thermogenesis.

Metabolic changes in rats fed a low protein diet during post-weaning growth

Metabolic changes in rats fed a low protein diet were investigated during 3 weeks after weaning using lactalbumin (LP) as dietary protein source. The energy intake was higher and the weight gain lower in rats fed the low protein diet (6%, LP group) than in control rats (13% lactalbumin, C group). Low protein diet induced no changes in plasma glucose, free fatty acids, or triacylglycerol concentrations; however, plasma protein and urea concentrations were lower in LP than in C rats. Plasma free T3 was higher in LP than in C rats (+38%, day 21) and insulin progressively decreased during the experimental period (-56%, day 21) without change in glucagon. Liver glycogen and triacylglycerol concentrations (+40% and +180%, respectively, day 21), and cytosolic and mitochondrial redox states increased (+100% and +100%, day 21), and protein concentration was decreased (-15%, day 21). Pyruvate kinase (PK) and malic enzyme activities were higher in LP than in C rats throughout the experiment (+80% and +210%, respectively, day 21), and glucose-6-phosphate dehydrogenase (G6PDH) activity progressively decreased (-65%, day 21). Phosphoenolpyruvate carboxykinase (PEPCK) activity increased after 2 weeks on a LP diet (+35%, day 21) and fatty acid synthetase (FAS) activity increased only during the first week on the diet (+100%, day 7). Such hormonal and metabolic changes appeared to be associated with the development of a futile energy-wasting cycle between pyruvate and phosphoenolpyruvate.

Effects of dietary carbohydrate and phenotype on thyroid hormones and brown adipose tissue locularity in adult LA/N-cp rats

1. Groups of lean and corpulent LA/N-cp rats were fed isoenergetic diets containing, 54% carbohydrate as maize starch (MS) or sucrose (SU), 20% protein, 16% mixed fats, plus other essential nutrients and fiber from 1.5-9 months of age. Final body weights of corpulent rats were 2-3 times those of their lean littermates, and were greater with SU than MS diet in both phenotypes. 2. Interscapular brown adipose tissue (IBAT) mass was greater in corpulent than lean and was greater with SU than MS diet in lean but not corpulent rats. IBAT cell diameters and adipocyte volumes were generally similar in both phenotypes, and were not markedly affected by dietary carbohydrate type. 3. Brown adipocyte locularity profiles were qualitatively similar in both phenotypes, and were morphologically indicative of thermogenic activity in both phenotypes. Locule profiles of corpulent animals contained a greater proportion of thermogenically less active types IV and V brown adipocytes than similarly fed lean animals, however, and locule distribution profiles were not influenced by diet. 4. Serum T3 concentrations were similar in both phenotypes, were greater in SU than MS lean rats and were not influenced by diet in the corpulent phenotype. In contrast, serum thyroxine concentrations and percent thyroxine uptake were not influenced by diet or phenotype. 5. These results are consistent with a partial impairment in BAT-mediated thermogenic activity in the corpulent phenotype and suggest that obesity in this strain may be due to factors other than biochemically defective brown adipose tissue thermogenesis.

Time-course effects of protein malnutrition on hepatic fatty acids delta 6 and delta 5 desaturation in the growing rat

1. In growing rats, the time-course effects of giving a normal-protein diet (200 g casein/kg; NP) for 52 d, a low-protein diet (20 g casein/kg; LP) for 52 d and a LP diet for 26 d followed by balanced refeeding (200 g casein/kg; BR) for 26 d, on the fatty acid composition of liver total lipids and microsomal phospholipids were investigated together with delta 6- and delta 5-microsomal desaturase activities. 2. The oleic acid content (mg/g tissue) of liver total lipids increased progressively with the LP diet, while linoleic acid was increased only at days 7 and 52. 20:3 omega 6, 20:4 omega 6, 22:5 omega 6 and 22:6 omega 3 fatty acids decreased during the period on the LP diet. BR for 7 d was sufficient to restore the fatty acid composition of total lipids to control values. Changes in the fatty acid composition of liver microsomal L-alpha-phosphatidylcholines were observed only after 52 d on the LP diet; the proportions (% w/w total fatty acids) of 18:0, 20:3 omega 6 and 20:4 omega 6 fatty acids decreased while oleic acid increased. The fatty acid composition of L-alpha-phosphatidylethanolamines was less affected. 3. delta 6- and delta 5-desaturase activities decreased to 20-30% of their original values after 2 d on the LP diet; a smaller deficit prevailed after 14 d but disappeared after 25 d, to appear again after 52 d. As early as day 2 of BR, desaturase activities were greatly recovered and returned to control values at day 13. 4. The present work shows that modifications in microsomal delta 6- and delta 5-desaturase activities are not strictly paralleled by the changes in the composition of fatty acids of liver total lipids and microsomal phospholipids.

Protein, carbohydrate, and ethanol consumption: interactions in AA and ANA rats

Female rats of the alcohol-preferring AA line were given a choice between protein, carbohydrate, and fat sources. Subsequent free access to alcohol decreased their intake of carbohydrate but not of protein or fat. The individual alcohol intakes were negatively correlated with the carbohydrate intakes (-0.76) and with the alcohol-induced changes in carbohydrate intake (-0.83), but positively correlated with the concurrent protein intakes (0.78). The alcohol consumption and ethanol elimination rate of AA rats were subsequently found to vary directly with the protein content (5, 10, 20 and 40% by energy) of the premixed diet given to them--they drank more than 9 times more ethanol on the 40% than on the 5% protein diet--but the alcohol intake of the alcohol-avoiding ANA rats was not affected by protein intake. The results clearly indicate that the three macronutrients are related to alcohol consumption in different ways, suggesting that protein intake affects the selection of alcohol of AA rats through a factor correlated to ethanol elimination (but not through a ceiling effect from the rate of elimination) and that the alcohol in turn reduces carbohydrate consumption.

Effect of protein malnutrition on salmonellosis and fever

Protein-malnourished rats had greater numbers of bacteria in their livers and spleens compared with numbers in control rats following a sublethal intraperitoneal dose of Salmonella typhimurium. However, the febrile responses of both groups of rats to infection were similar. The ability to mount a normal febrile response does not necessarily reflect the ability of the host to contain an infection.

Effect of a selective beta 2-adrenergic agonist (clenbuterol) on energy balance and body composition in normal and protein deficient rats

In rats fed a normal (22% protein) diet, injection of clenbuterol (1 mg/kg/d for 21 d) did not affect energy intake, energy expenditure or weight gain, but reduced energetic efficiency, and fat and energy gains and increased body protein content. Presenting a low-protein (8%) diet reduced energy intake, gain and efficiency, body protein content and the mass of the gastrocnemius muscle when compared to rats fed the control diet. Injection of the protein-deficient rats with clenbuterol (1 mg/kg/d for 21 d) caused hypophagia and reduced body weight and energy gains, energy expenditure and total body fat. However, the total body content of protein was not significantly reduced and the percentage of body protein in this protein deficient, clenbuterol-treated group was greater than that of untreated rats on both the high- and low-protein diets. The ratio of body protein to fat following clenbuterol treatment was increased by over 50% in both normal and protein-deficient rats. The results show that in protein deficient animals, clenbuterol treatment may help conserve body protein at the expense of fat, resulting in a smaller, but leaner body mass.

Effect of a carbohydrate-restricted, calorie-reduced diet on the growth of young rats and on serum growth hormone, somatomedins, total thyroxine and triiodothyronine, free T4 index, and total corticosterone

We have studied the effect of a carbohydrate-restricted, calorie-reduced diet on the growth of young rats and on serum levels of GH, somatomedins [insulin-like growth factors (IGFs) I and II], total T4 and T3, free T4 index, and total corticosterone. Experimental animals consumed the same quantities of protein and fat as controls, but only 50.3% as much carbohydrate and 76% as many calories. While the experimental group grew at 69.4% of the control rate, their mean (+/- SEM) GH level (175.7 +/- 36.9 ng/mL) was not significantly different from that in the control group (180 +/- 30 ng/mL). In contrast, serum total IGF and IGF-I, while not correlated with serum GH levels, were significantly correlated in all animals with body weight (r = .87 and r = .82, respectively, P less than .01) and tail length (r = .61 and r = .62, respectively, P less than .01). The somatomedin levels of the carbohydrate-restricted rats were significantly lower than those of their age-matched, but not weight-matched, controls by the eighth day of study. Serum T4, T3, and free T4 index were not significantly different in these two groups, while total corticosterone in the experimental group (245 +/- 73 ng/mL) was slightly lower than in controls (292 +/- 80 ng/mL, P less than .05). These data indicate that by restricting carbohydrate intake we have compromised the anabolic use of dietary protein by growing rats, resulting in a retardation of growth and a reduction in serum total IGF and IGF-I levels.

The effect of dietary protein and energy restriction on heat production and growth costs in the young rat

1. The effect of dietary protein and energy restriction on heat production and growth costs has been examined in rats fed on a marginal (MP) or high (HP) protein diet, containing 9.2% or 22% respectively of the gross energy content as casein. Diets were given either ad lib. or at approximately 25, 50 or 75% of the ad lib. intake. 2. Heat production (kJ/kg body-weight (W)0.75 per d) was increased by 23% in rats fed on the MP diet ad lib., as compared with their HP controls (P less than 0.01). 3. Factorial analysis of the data showed that the overall cost of energy deposition (kJ/kJ; Ee) was elevated on the MP diet (MP 1.7, HP 1.28; P less than 0.001). Maintenance requirements (kJ/kg W0.75 per d) for zero energy balance were unchanged (MP 562, HP 573). 4. The partial energy cost of protein deposition (Ep) varied with dietary manipulation. If the partial energy cost of fat deposition (Ef) was assumed constant at 1.25 kJ/kJ, and maintenance requirements were assumed to vary with metabolic body size (W0.75), Ep was elevated on the MP diet. On both diets, Ep was reduced at low energy intakes. 5. The significance of these results is discussed in the context of current approaches to the analysis and interpretation of findings describing dietary induced changes in the rate of heat production.

Relations between enzyme activities connected with energy metabolism and parameters of food energy utilization in young and adult rats. Part 1. Studies on dietary effects on weight, body composition and energy gain

Weaned male Wistar rats were fed ad libitum besides standard pellets a normal-protein (NP), a low-protein (LP) and a high-fat (HF) diet for different periods of time. In comparison to rats on the NP diet the body weight of the LP group was significantly lower after seven weeks feeding, not after a duration of about forty weeks. No remarkable diet-related differences were detected by determination of the mean body composition and of the relative gross energy content of the body neither after seven nor forty weeks. Total gross energy intake was practically identical both for the NP and LP rats irrespective on the duration of the feeding period. A significantly lower quotient of body energy gain/total gross energy intake under the protein-restrictive LP diet after seven weeks suggests the expression of an energy dissipation obviously no longer visible after a long time feeding period.

Effects of pre- and early postnatal protein malnutrition on carcass composition and lipoprotein lipase activity in male rats

Little is known about the effects of pre- and early postnatal protein malnutrition on energy storage (e.g., carcass lipid) and expenditure (e.g., brown adipose tissue [BAT] thermogenesis) and their reversibility by nutritional rehabilitation. Therefore, the purpose of these experiments was to examine the permanence of prenatal and early postnatal protein malnutrition on energy balance in rats. Five weeks before mating and through gestation adult female rats were fed either a 25 or 8% casein diet (designated 25 or 8). Diet reversals were performed at birth and/or at weaning (designated B or W) and the pups were cross-fostered at birth. Thus, the groups were: 25-25B (controls), 8-25W (gestational and lactational protein malnutrition, 8-25B (gestational protein malnutrition), and 25-8B-25W (lactational protein malnutrition). Animals were weighed and sacrificed 200-250 days postpartum for carcass composition. Retroperitoneal white adipose tissue (RWAT) and interscapular BAT (IBAT) wet weights and lipoprotein lipase (LPL) activity were also measured in the 25-25B and 8-25W groups. Nutritional rehabilitation at birth (8-25B) resulted in normal body weights as adults. Lactational protein malnutrition (25-8B-25W) resulted in intermediate body weights to the controls (25-25W), which had the greatest weights, and the 8-25W group, which had the lowest weights. The 8-25W and 25-8B-25W rats also had significantly decreased carcass wet weight and total body water, fat and fat-free dry mass relative to the 25-25B and 8-25B groups, the latter two of which did not differ in their carcass composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Triiodothyronine (T3) neogenesis in lean and obese LA/N-cp rats

Pre-obese LA/N-cp rats consumed more food and gained weight more rapidly than their lean littermates, and measures of adipose tissue depots indicated that the excess weight was deposited principally as carcass fat. Serum T3 concentrations and resting metabolic rates were lower in corpulent than in lean animals, consistent with a greater efficiency of weight gain in those animals. In vitro measures of T3 neogenesis from T4 were lower in corpulent than in lean animals in liver, kidney, and skeletal muscle and greater in interscapular brown adipose tissue. The intracellular generation of T3 from T4 is a fundamental component of the normal adaptive response to alterations in diet and environment, and is an essential prerequisite for the expression of non-shivering thermogenesis. These results are consistent with a functional impairment in the activity of the enzyme T4-5'-deiodinase in peripheral tissues, and suggest that this impairment is contributory if not causative of obesity in this strain of rat.

Maternal malnutrition in the rat: effects on food intake and body weight

The effects of dietary protein level on food intake and body weight were examined in adult female rats during a 35-day pre-mating period and during gestation and lactation. During the pre-mating period, no differences in daily food intake were observed among rats fed a 6% casein, 8% casein or 25% casein diet. However, during this period, rats fed the 6% casein diet gained significantly less weight than those with ad lib access to the 8% or 25% casein diets or than rats pair-fed the 25% casein diet in amounts equivalent to that consumed by rats in the 6% or 8% casein groups. Additionally, rats fed the 6% casein diet displayed decreased efficiency of energy utilization, calculated as weight gain per 100 kilocalories consumed, relative to rats fed the 8% or 25% casein diets. No differences in food intake were observed among the groups during gestation. However, rats fed the 6% casein diet gained less weight than rats fed the 8% or 25% casein diets. During lactation rats fed either the 6% or 8% casein diet consumed significantly less food than animals given the 25% casein diet ad lib. During the second week of lactation, rats receiving ad lib access to the 25% casein diet gained weight while those receiving the 6% or 8% casein diets continued to lose weight. At parturition, body weights of pups did not differ as a function of dietary condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonshivering thermogenesis in the diabetic SHR/N-cp (corpulent) rat

The effects of isoenergetic sucrose and starch-based diets on thermogenesis were investigated in young adult, male, lean and corpulent SHR/N-cp rats. Corpulent rats gained weight 1.5 times more rapidly than lean, and sucrose diets resulted in more rapid weight gains in both phenotypes. Rates of resting and of norepinephrine-stimulated oxygen consumption were similar in both groups of lean rats and in sucrose-fed corpulent rats, but were decreased in starch-fed corpulent rats. The thermic response to injected norepinephrine occurred normally in all groups. Colonic and rectal temperatures were greater in lean than in corpulent rats. Acute cold exposure (5 degrees C) resulted in decreases in rectal but not colonic temperature in lean rats fed both diets, but resulted in lower temperatures at both sites in corpulent rats, with the greatest decreases being observed in the starch fed corpulent rats. Fifty percent of the corpulent but none of the lean rats succumbed within 24-48 hours following cold exposure. Urinary vanilmandelic acid (VMA) excretion was greater in lean than in corpulent rats, and the sucrose diet induced a greater increment in urinary VMA excretion in lean rats than in corpulent rats. These results are consistent with an impaired activation of sympathetically-mediated thermogenesis via nutritional or environmental stimuli in the corpulent genotype of the SHR/N-cp rat in concert with an economy in energy expenditure which may be contributing factors in the causation of their obese state.

Responses to oral methionine supplementation in sheep fed on kale (Brassica oleracea) diets containing S-methyl-L-cysteine sulphoxide

1. Responses to twice-weekly oral supplementation with 4.0 g methionine were measured with lambs (27 kg) grazing kale (Brassica oleracea) for 10 weeks (Expt 1). In a second experiment with sheep fed on kale at hourly intervals, rumen fractional outflow rates of CrEDTA and ruthenium Tris(1,10 phenanthroline) markers were measured from the rates of decline in their concentrations. Rumen turnover of S-methyl-L-cysteine sulphoxide (SMCO) and of carbohydrate (CHO) constituents were also measured. The kale fed contained 11.4 g SMCO/kg dry matter and the ratio, readily-fermentable: structural CHO was high at 2.9. 2. Severe haemolytic anaemia, associated with low live-weight gain (LWG), occurred in the lambs during the initial 5 weeks of grazing, due to rumen fermentation of SMCO. Oral methionine supplementation raised plasma concentrations of methionine and cysteine, increased wool growth rate, and increased LWG during the initial 5 weeks. Methionine supplementation also increased rumen pool and plasma SMCO concentrations, suggesting reduced rumen SMCO fermentation. 3. In Expt 2, rumen degradation rate of SMCO (1.2/h) was calculated to be twice as fast as that of the most rapidly fermented dietary CHO constituents and eight times faster than the rate of water outflow (0.16/h), thus explaining its virtually complete rumen degradation and toxicity in brassica diets. It was estimated that 1.2 g of each 4.0 g methionine administered would have escaped rumen degradation, due to the high rate of water outflow from the rumen. 4. Disappearance rates of CHO constituents from the rumen were as predicted for normal ruminant diets, showing that rumen metabolism of SMCO did not have a depressive effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Endocrine responses of protein-malnourished rats infected with Nippostrongylus brasiliensis (Nematoda)

During the course of a primary infection of Nippostrongylus brasiliensis in protein-malnourished rats, plasma concentrations of corticosterone were found to decrease from 0.89 +/- 0.03 at the start of the infection to 0.28 +/- 0.08 mumol/l, 9 days post-infection (p.i.). Similarly, adreno-corticotrophic hormone levels were also observed to fall from 62.09 +/- 12.06 to 20.54 +/- 1.81 by 5 days p.i. and to 35.12 +/- 16.61 nmol/l by 9 days p.i. However, no significant changes were seen in the dry weight of the adrenal glands other than those expected in relation to changes in body weight. Concentrations of both plasma tri-iodothyronine and thyroxine were also severely depleted over the same period from 5.33 +/- 0.34 to 1.09 +/- 0.42 and 104.43 +/- 10.4 to 34.12 +/- 8.95 nmol/l respectively. This was considered not to be due to any change in the capacity of the plasma to bind these hormones. Results for insulin were highly variable, but overall were lower from protein-malnourished rats than results documented for well-nourished rats and a reduction from 18.07 +/- 3.17 to 6.08 +/- 2.18 mu units/ml, 9 days p.i. was observed. The results are discussed in relation to the role of these hormones in protein metabolism in a protein-malnourished animal.