BSB: a new mouse model of multigenic obesity

We report here a new mouse model of multigenic obesity. Backcross progeny ((C57BL/6J x Mus spretus)F1 x C57BL/6J), designated as BSB mice, range from 1% to 50% body fat. Since both parental strains are relatively lean, the wide range of the phenotype in the BSB mice indicates the involvement of multiple genes to produce obesity. Obesity in BSB mice results from increases in both intra-abdominal and subcutaneous fat and is associated with hyperinsulinemia, hyperglycemia, and hyperlipidemia. Female and male BSB mice do not differ in the degree of obesity obtained. Stimulated plasma corticosterone levels are reduced in obese male and female mice. The development of appropriate genetic markers and statistical methods have made it feasible to analyze quantitative polygenic traits in animal models by employing F2 or backcross progeny. Thus, this BSB model is uniquely suited to the genetic analysis of the multifactorial quantitative trait of obesity and its associated phenotypes.

Studies of natural allele effects in mice can be used to identify genes causing common human obesity

Although genes causing rare Mendelian forms of human obesity have provided much useful information about underlying causes of obesity, these genes do not explain significant proportions of common obesity. This review presents evidence that animal models can be used to uncover subtle genetic effects on obesity and can provide a powerful rigorous compliment to human association studies. We discuss the advantages of animal models of obesity, various approaches to discovering obesity genes, and the future of mapping and isolating naturally occurring alleles of obesity genes. We review evidence that it is important to map naturally occurring obesity genes using quantitative trait locus (QTL) mapping, instead of mutagenesis and knockout models because the latter do not allow study of interactions and because naturally occurring obesity alleles can interfere with cloning from mutagenesis projects. Because a substantial percentage of human obesity results from complex interactions, the underlying genes can only be identified by direct studies in humans, which are still very difficult, or by studies in mice that begin with QTL mapping. Finally, we emphasize that animal model studies can be used to prove that a specific gene, only associated with obesity in humans, can indeed be the underlying cause of obesity in mammals.

Integrated methods to solve the biological basis of common diseases

Biological variations influence population variations of many common traits. Identification of the biological basis of many common diseases has been particularly difficult, but new reagents and analytical tools will greatly facilitate this process. The goal of this review is to discuss how to identify the biological basis of common traits by using mouse models. No single method will work for all traits. Understanding complex problems will require broadly based holistic approaches that use a wide array of tools and resources. A multiplicity of developed methods together provide the tools needed to identify the biological basis of any common trait. These tools, whole-genome linkage maps, maps of expressed genes, and statistical methods, deal with the complexities of multiple loci or correlated traits. This review provides some criteria for making choices about the likely productive approaches at each stage in the process of finding genes that influence common traits.

Identification of an obesity quantitative trait locus on mouse chromosome 2 and evidence of linkage to body fat and insulin on the human homologous region 20q

Chromosomal synteny between the mouse model and humans was used to map a gene for the complex trait of obesity. Analysis of NZB/BINJ x SM/J intercross mice located a quantitative trait locus (QTL) for obesity on distal mouse chromosome 2, in a region syntenic with a large region of human chromosome 20, showing linkage to percent body fat (likelihood of the odds [LOD] score 3.6) and fat mass (LOD score 4.3). The QTL was confirmed in a congenic mouse strain. To test whether the QTL contributes to human obesity, we studied linkage between markers located within a 52-cM region extending from 20p12 to 20q13.3 and measures of obesity in 650 French Canadian subjects from 152 pedigrees participating in the Quebec Family Study. Sib-pair analysis based on a maximum of 258 sib pairs revealed suggestive linkages between the percentage of body fat (P < 0.004), body mass index (P < 0.008), and fasting insulin (P < 0.0005) and a locus extending approximately from ADA (the adenosine deaminase gene) to MC3R (the melanocortin 3 receptor gene). These data provide evidence that a locus on human chromosome 20q contributes to body fat and insulin in a human population, and demonstrate the utility of using interspecies syntenic relationships to find relevant disease loci in humans.

Mapping of mouse obesity genes: A generic approach to a complex trait

Identification of genes underlying any complex trait such as obesity is an important and difficult problem in genetics. Traditional candidate gene approaches cannot be relied on to identify all of the genes influencing a complex trait, and positional cloning is very laborious. With the advent of new tools and methods, however, comprehensive approaches to the identification of any genes underlying complex traits are now available. Quantitative trait locus (QTL) mapping is a general technique to map Mendelian factors influencing complex traits. The QTL approach involves the crossing of two strains that differ in the trait of interest to produce F2 or back-cross progeny, individually phenotyping and genotyping each progeny, and statistically associating the typed markers and the phenotype. QTL mapping has been used in the last 4 years to map genes for a wide variety of traits, including body weight and growth, obesity, atherosclerosis and susceptibility to cancer in the mouse, and hypertension, hyperactivity and arthritis in the rat. QTL mapping has also been used to map genes in pigs, poultry, cows, fish and plants. Once a trait has been located in a chromosomal subregion, identifying the underlying gene remains a significant problem. A monogenic model must be developed, isolating one gene influencing a trait from other genes affecting the same phenotype. Then the positional candidate strategy, which relies on a combination of mapping to a chromosomal subregion followed by a survey of the interval to see if attractive candidates reside there, becomes practical.

Peripheral 3-hydroxybutyrate and food intake in a model of dietary-fat induced obesity: effect of vagotomy

We have examined the effect of peripheral 3-hydroxybutyrate injections on food intake and the contribution of the vagus nerve in the resistance to dietary fat-induced obesity in a rodent model. S 5B/Pl rats, which are resistant to dietary-fat induced obesity, and Osborne-Mendel rats, which are sensitive, were adapted to reverse light cycle. Food intake was measured for 24 h following the injection of 3-hydroxybutyrate, lactate, or glycerol (all 5 mMol/kg0.75, SC) at the onset of dark. Three-hydroxybutyrate reduced food intake (p < 0.0001) in S 5B/Pl rats only. Lactate reduced food intake slightly (p < 0.009) in both strains and glycerol had no effect on food intake. In a second experiment, S 5B/Pl and Osborne-Mendel rats were adapted to a high-fat diet and were then subjected to either selective hepatic vagotomy or sham operation. Vagotomy had no effect on weight gain of Osborne-Mendel rats but allowed weight gain in S 5B/Pl rats (p < 0.0001). Even in vagotomized S 5B/Pl rats, however, blood 3-hydroxybutyrate levels were inversely associated (r = -0.50) with food intake. These data suggest that the hepatic vagus nerve may contribute to the resistance of S 5B/Pl rats to dietary-fat induced obesity, but the data do not rule out a strictly central role for the regulation of food intake by 3-hydroxybutyrate in this strain.

Identification of four chromosomal loci determining obesity in a multifactorial mouse model

We previously described a new mouse model for multigenic obesity, designated BSB. We now report the use of a complete linkage map approach to identify loci contributing to body fat and other traits associated with obesity in this model. Four loci exhibiting linkage with body fat, or with the weights of four different fat depots, residing on mouse chromosomes 6, 7, 12, and 15, were identified and confirmed by analysis of additional BSB mice. Each of the four loci differed with respect to their effects on the percent of body fat, specific fat depots and plasma lipoproteins. The loci exhibited allele-specific, non-additive interactions. A locus for hepatic lipase activity was co-incident with the body fat and total cholesterol loci on chromosome 7, providing a possible mechanism linking plasma lipoproteins and obesity. The chromosome 7 locus affecting body fat, total cholesterol and hepatic lipase activity was isolated in congenic strains whose donor strain regions overlap with the chromosome 7 BSB locus. These results provide candidate genes and candidate loci for the analysis of human obesity.

Liver fatty acid composition correlates with body fat and sex in a multigenic mouse model of obesity

To determine whether there is altered liver lipid-fraction fatty acid distribution in a multigenic obese mouse model, we examined livers from eight lean (0.2-4.2% carcass fat), seven intermediate (5.7-13.8%), and five obese (20.2-48.7%) backcross progeny [(C57BL/6J x Mus spretus) x C57BL/6J] aged 2-3 mo. Thirteen males and seven females were fed a nonpurified stock diet. Liver lipid fractions were separated and fatty acids quantitated by thin-layer and gas chromatography. There was a significant effect of obesity on 18:2 omega 6 in liver phospholipids (PL), cholesteryl esters, and triglycerides. PL 18:2 omega 6 was negatively correlated with carcass fat (r = -0.74, P < 0.001); 20:3 omega 6 was elevated in PL with increased obesity (P < 0.0001), and was correlated with carcass fat (r = 0.92, P < 0.0001); and 20:4 omega 6 in PL did not differ with obesity status. PL 20:3 omega 6 and 20:4 omega 6 were lower in males (P < 0.01 and 0.02, respectively) than in females. We conclude that obesity and sex affect distribution of omega 6 essential fatty acids in mouse liver lipid fractions.

Coincidence of genetic loci for plasma cholesterol levels and obesity in a multifactorial mouse model

We have examined backcross progeny derived from a cross of Mus spretus with C57BL/6J, that range from 1 to 50% carcass lipid (n = 215), and from 22 to 130 mg/dl plasma total cholesterol (n = 238). Statistical analysis revealed that distal mouse chromosome 7 exhibits significant linkage both to plasma total cholesterol (likelihood of the odds [LOD] 5.8) and to carcass lipid (LOD 3.8). A locus on chromosome 6 also shows significant linkage to plasma total cholesterol (LOD 5.6), but no linkage to carcass lipid. Neither chromosomal region contains any previously mapped genes likely to influence lipoprotein metabolism, indicating that novel genetic factors contributing to plasma lipoprotein levels have been identified.

d-fenfluramine in a rat model of dietary fat-induced obesity

d-Fenfluramine is an appetite suppressant drug that acts by releasing serotonin from axon terminals and inhibiting its reuptake. S 5B/P1 rats, which are resistant to dietary-fat induced obesity, and Osborne-Mendel rats, which are sensitive, were adapted to ad lib feeding of either a low- or high-fat diet. d-Fenfluramine (10 mg/kg, IP) was injected daily for 12 days. Other than a slightly greater suppression of food intake in Osborne-Mendel rats, there was little difference in response to d-fenfluramine between S 5B/P1 and Osborne-Mendel rats eating the low-fat diet. However, in Osborne-Mendel rats d-fenfluramine completely abolished the excess food intake and weight gain associated with the high-fat diet. Purine nucleotide (GDP) binding on day 13 was higher in S 5B/P1 rats than in Osborne-Mendel rats and was increased by d-fenfluramine in animals of both strains eating the low-fat diet. The high-fat diet increased GDP binding only in S 5B/P1 rats and blocked the fenfluramine-induced increase in GDP binding in both strains. We speculate that d-fenfluramine blocks a feeding reward system stimulated by the high-fat diet.

Whole body insulin sensitivity in Osborne-Mendel and S 5B/Pl rats eating a low- or high-fat diet

To determine whether whole body insulin sensitivity differs between a rat strain that does not (S 5B/Pl) and a strain that does [Osborne-Mendel (OM)] become obese when eating a high-fat diet, we performed euglycemic clamp studies in animals from each strain during low- and high-fat feeding. Clamps were performed after 2 days ("initial clamp") and 9 days ("final clamp") on each diet. Plasma glucose and insulin levels during the final 60 min of initial and final clamps were similar in S 5B/Pl and OM rats regardless of diet. Insulin sensitivity, measured as the glucose clearance rate during the final 60 min of the clamp, averaged 35 +/- 3 ml.kg-1.min-1 in S 5B/Pl rats after 2 days on a low-fat diet. This did not change significantly during an additional 7 days on the low-fat diet. The high-fat diet was associated with a 13% reduction in insulin sensitivity after 2 days and a 30% reduction after 9 days in S 5B/Pl rats. OM rats exhibited similar patterns of insulin sensitivity during low- and high-fat diets, albeit at lower insulin sensitivity overall (P < 0.0005 vs. S 5B/Pl). Mean glucose clearance after 2 days on the low-fat diet was 27 +/- 2 mg.kg-1.min-1 and did not change significantly during seven more days of low-fat feeding. The high-fat diet was associated with a 19% reduction in glucose clearance after 2 days and a 38% reduction after 9 days in OM rats. The magnitude of reduction in insulin sensitivity during high-fat diets did not differ significantly between strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac effects of starvation and semistarvation diets: safety and mechanisms of action

A major concern with the use of starvation or semistarvation diets for weight reduction in severely obese people has been the reports of sudden death due to ventricular arrhythmias. Obesity per se is associated with cardiovascular changes, including left ventricular hypertrophy and prolongation of the QT interval. With weight loss, the mass of the heart and left ventricle decrease, but some signs of left ventricular dysfunction remain. The effect of weight loss on the electrocardiogram abnormalities of obesity appears to depend upon diet duration and upon whether protein and mineral nutritional status is maintained. Copper, potassium, and magnesium deficiencies may play important roles in promoting an electrically unstable heart. Stress, by eliciting autonomic imbalance, may act upon an electrically unstable heart to provoke acute arrhythmias in a subset of the obese population with QT interval prolongation.

Myocardial Mass in Morbidly Obese Patients and Changes with Weight Reduction

Cardiac weight was determined at autopsy in 27 morbidly obese, but otherwise healthy men (mean weight 168 kg) and women (mean weight 138 kg) who died suddenly, prior to, or shortly after gastric restriction operations for relief of obesity. They had lost no weight. Post-mortem examination revealed no cardiac or other pathology explaining the cause of death. Cardiac weight was also measured in 25 men and women of equivalent baseline weight and body mass index who, after operation, subsisted on a hypocaloric diet for 3-4 months after operation, but then died suddenly. Mean weight losses of this latter group were 45.8 kg in men and 32.9 kg in women. No cardiac abnormalities and no organic causes of death were found at autopsy. Decreases in heart weight were calculated. The baseline measurements demonstrated that cardiac weight in the healthy obese rose with increasingly severe obesity in both sexes, but the increase tended to lessen with more extreme obesity. The generally quoted figures of cardiac weight as a fraction of body weight are 0.043 and 0.040% for men and women, respectively. In the group of morbidly obese men, cardiac weight was 0.035% of body weight or 16% lower than predicted. In morbidly obese women, cardiac weight was 0.030% of body weight or 25% lower than predicted. In men, a 28% body weight reduction due to dietary restriction resulted In a proportionately similar 20% decrease in cardiac weight. In contrast, in women after a 27% loss of body weight, cardiac weight decreased only 5%. Severe dietary restriction with a drastic body weight loss did not result in a disproportionate decrease of cardiac weight in either sex, when final body weight had remained above or in the normal range.

Effect of a high-fat diet on firing rate of sympathetic nerves innervating brown adipose tissue in anesthetized rats

Three experiments have examined the effects of ad lib and forced intake of a high-fat diet on sympathetic firing rate to brown adipose tissue. Seven days after beginning of ad lib intake of either a low-fat or high-fat diet, sympathetic activity was not significantly different in either group nor was it significantly different from the values obtained in animals measured at the switch from the chow to a semisynthetic high- or low-fat diet. After 22 days on the semisynthetic diet, however, the sympathetic firing rate of animals eating the high-fat diet had decreased nearly 25% and was significantly lower than the animals maintained on the semisynthetic low-fat diet or animals studied at the transition from the chow to the low-fat diet. In a second experiment animals were tube-fed for 3, 6 or 9 weeks on a high- or low-fat diet. Sympathetic firing rate of the rats eating the low-fat diet was higher at all three times, but the difference decreased with longer feeding. To eliminate differences in food intake, animals were tube-fed a moderate- or high-fat liquid diet three times a day for six days. The 80 kcal/day intake produced a steady weight gain in both groups. Liver weight, retroperitoneal white adipose tissue weight, and interscapular brown adipose tissue weight were all significantly greater in the animals fed the high-fat diet. Sympathetic firing rate, however, was significantly lower in the animals fed the high-fat semisynthetic diet as compared to animals fed the moderate-fat diet. These data show the high-fat diets are associated with a reduction in sympathetic activity to brown adipose tissue.

Brain 3-hydroxybutyrate, glutamate, and GABA in a rat model of dietary obesity

Whole brain concentrations of 3-hydroxybutyrate, glutamate and gamma-aminobutyric acid (GABA) have been measured in two strains of rats with differing susceptibility to obesity. S 5B/Pl rats are resistant to developing obesity when eating a high-fat diet, whereas Osborne-Mendel rats readily develop obesity when eating the same diet. We tested the hypotheses that brain 3-hydroxybutyrate, glutamate and GABA differ between S 5B/Pl rats and Osborne-Mendel rats, and that these substrates/neuroregulators are altered when eating a high-fat diet primarily in S 5B/Pl (resistant) rats. Blood and brain 3-hydroxybutyrate concentrations were higher in S 5B/Pl rats than in Osborne-Mendel rats (p less than 0.05) but diet effects were not significant. Brain glutamate concentration, like 3-hydroxybutyrate, was higher in S 5B/Pl rats than in Osborne-Mendel rats (p less than 0.01) and was not affected by adding fat to the diet. Brain GABA differed only slightly between strains but increased after adding fat to the diet (p less than 0.05) in both strains with a greater increase occurring in S 5B/Pl rats. The brains of S 5B/Pl rats are chronically exposed to higher levels of 3-hydroxybutyrate and glutamate than are those of Osborne-Mendel rats. Thus, 3-hydroxybutyrate is a potential signal in the regulation of body weight. Brain GABA increases with fat feeding, especially in S 5B/Pl rats, suggesting that the ability to adjust to an energy dense diet may be through suppression of food intake by elevated brain GABA.

Effect of carbohydrate refeeding on free fatty acids after a fast in obese diabetic and obese non-diabetic females

The metabolic effects of refeeding with oral or intravenous carbohydrate were studied in obese women after ten or 14 days of fasting. Seven patients were refed with protein-free fruit juice for a total of 250 g of carbohydrate (1,000 kcal) over ten hours. The juice was sipped continuously throughout this time, causing a drop in free fatty acids (FFA) from 1.07 +/- 0.08 to 0.61 +/- 0.05 mmol/L (P less than .01) over the first four hours. Over the next four hours, despite continuous ingestion of the carbohydrate and elevated plasma glucose (132 +/- 9 mg/dL) and insulin (2.81 +/- 0.86 ng/mL) (1 ng/mL = 25 microU/mL), FFA rose to 0.99 mmol/L (P less than .01). Similar results were obtained in five patients refed with similar amounts of oral glucose and four patients who received an equivalent amount of glucose intravenously (IV). Refeeding with carbohydrate of obese diabetic and non-diabetic women after a two-week fast caused an abrupt decrease in FFA that was followed after four hours by an increase in FFA and glycerol, despite continued ingestion of carbohydrate glucose and insulin.

Experimental obesity: a homeostatic failure due to defective nutrient stimulation of the sympathetic nervous system

The basic hypothesis of this review is that studies on models of experimental obesity can provide insight into the control systems regulating body nutrient stores in humans. In this homeostatic or feedback approach to analysis of the nutrient control system, we have examined the afferent feedback signals, the central controller, and the efferent control elements regulating the controlled system of nutrient intake, storage, and oxidation. The mechanisms involved in the beginning and ending of single meals must clearly be related to the long-term changes in fat stores, although this relationship is far from clear. Changes in total nutrient storage in adipose tissue can arise as a consequence of changes in the quantity of nutrients ingested in one form or another or a decrease in the utilization of the ingested nutrients. A change in energy intake can be effected by increased size of individual meals, increased number of meals in a 24-hour period, or a combination of these events. Similarly, a decrease in utilization of these nutrients can develop through changes in resting metabolic energy expenditure which are associated with one of more of the biological cycles such as protein metabolism, triglyceride for glycogen synthesis and breakdown, or maintenance of ionic gradients for Na+ + K+ across cell walls. In addition, differences in energy expenditure related to the thermogenesis of eating or to the level of physical activity may account for differences in nutrient utilization.

Intracerebroventricular infusions of 3-OHB and insulin in a rat model of dietary obesity

We examined the effect of dietary fat on the response to 3-hydroxybutyrate (3-OHB) and insulin infused chronically into the third ventricle in three strains of rats with differing susceptibility to obesity induced by a high-fat diet: Osborne-Mendel rats are most susceptible; Sprague-Dawley-rats are intermediate; and S 5B/Pl rats are most resistant. Ten days after implantation of cannulas into the third ventricle, rats were fed either a low-fat diet or a high-fat diet for 14 days. On day 7, osmotic minipumps were attached to the ventricular cannulas. 3-OHB infusions (3.6 mumol/24 h) reduced food intake and body weight in Sprague-Dawley and Osborne-Mendel rats eating either diet. The dietary fat-resistant S 5B/Pl rats did not respond to the intracerebroventricular infusion of 3-OHB. The infusion of insulin (10 mU/24 h) lowered food intake and body weight in animals eating the low-fat (high-carbohydrate) diet but not in animals eating the high-fat diet. Diet profoundly affects the response to intracerebroventricular infusions of insulin but is without effect on the response to 3-OHB.

Effect of starvation and food intake on sympathetic activity

These studies have examined the effect of fasting and nutrient loads on sympathetic firing rate in three groups of rats that develop widely divergent degrees of obesity when eating a high-fat diet. Starvation of Sprague-Dawley rats for 24 or 48 h was associated with a decrease in basal sympathetic activity of nearly 25% in the first 24 h and of slightly greater than 30% in 48 h. This decline in sympathetic activity paralleled the loss of body weight and reduction in adipose tissue mass. After starvation for 48 h, Osborne-Mendel rats, which readily develop obesity when eating a high-fat diet, showed a greater decrease in basal sympathetic activity than did the diet-resistant S 5B/P1 rats. A single liquid 36-kcal intragastric meal was associated with an acute 30% increase in sympathetic firing rate in the overnight-fasted Sprague-Dawley rats. The values 3 h after the meal had returned halfway to normal, and by 6 h they were more than 85% of the way to normal. An intravenous injection of glucose produced a greater rise in sympathetic activity in diet-resistant S 5B/P1 rats than in the diet-sensitive Osborne-Mendel rats. These data are consistent with the hypotheses that sympathetic activity is positively related to nutrient status, that it varies between strains of rats, and that it can be acutely increased by an intragastric meal or by intravenous glucose.

Sudden cardiac arrest in morbidly obese surgical patients unexplained after autopsy

Sixty sudden and unexpected lethal cardiac arrests, with entirely negative findings on autopsy, were reported among 50,314 morbidly obese patients in the care of surgeons performing operations to achieve weight loss. This represented an extrapolated overall annual mortality rate of 65 deaths per 100,000 patients, about 40 times higher than the rate of unexplained cardiac arrests in a matched nonobese population. Eight sudden deaths occurred while waiting for obesity surgery and 22 had cardiac arrest within 10 days after the operation. Late postoperative deaths (more than 4 weeks postoperatively) occurred in 30 instances. A possible marker of a predisposition for sudden, unexpected cardiac arrest was an electrocardiographic abnormality; namely, a Q-Tc interval prolonged to greater than 0.43 seconds. This feature, present in 29 of 38 tracings, denoted increased susceptibility to malignant ventricular arrhythmias. The perioperative clustering of arrests implicated nonspecific stresses incident to otherwise uneventful operations as triggers of lethal dysrhythmias in the absence of organic cardiac disease. Anoxemia after abdominal surgery is an added hazard. Length of postoperative survival among the late deaths was found to be unrelated to degree of initial obesity or to magnitude of weight loss. Patients who died in the late postoperative phase were still grossly obese (mean weight 114.2 kg). Cardiac weights in patients who died within 10 postoperative days (12 patients) or after an average of 103 days (20 patients) were the same (464 and 469 g, respectively), indicating that myocardial mass had remained intact. The data do not suggest nutritional depletion or lean tissue loss as plausible explanations for the cardiac arrests. Screening and postoperative monitoring for Q-T interval prolongation is indicated. Prophylactic beta-blockade in this vulnerable subset of the morbidly obese population may be instituted in anticipation of obesity surgery. The attendant physiologic stresses should be minimized by appropriate measures.

Effects of repeated weight loss and regain on body composition in obese rats

To test the hypothesis that repeated loss and gain of weight through dieting will result in increasing fatness, 200-g female Sprague-Dawley rats were castrated and allowed to become obese on a high-fat diet for 6 wk. Two successive periods of severe food restriction (50% maintenance for 28 d and 25% maintenance for 21 d) were each followed by ad libitum refeeding on the high-fat diet until control body weights were attained. Percent body fat was determined indirectly from body density and total-body water at the end of each cycle. Restricted rats gained weight and attained control body weights on ad libitum feeding without overshooting these weights, and percentage body fat was not different from that of controls at the end of either cycle (cycle 1 22.3 +/- 1.7 vs 23.8 +/- 1.7%; cycle 2 19.0 +/- 1.1 vs 21.6 +/- 0.8%). Repeated cycles of weight loss and regain do not produce increased body fatness or decreased rate of weight loss in ovariectomized rats.

Brown fat thermogenesis in a rat model of dietary obesity

The effects of chronic feeding of a high-fat diet or a cafeteria-type diet on weight gain and thermogenesis in brown adipose tissue as measured by the binding of a purine nucleotide (guanosine 5'-diphosphate, GDP) to mitochondria of brown adipose tissue have been studied in two strains of rats that differ in their susceptibility to dietary obesity. S 5B/Pl rats, which are resistant to developing obesity when eating a high-fat diet or drinking sucrose solutions, have greater specific GDP binding in interscapular brown adipose tissue (IBAT) than do Osborne-Mendel rats, which are sensitive to fat-induced obesity. A high-fat diet, fed isoenergetically to the low-fat diet, did not increase the growth of IBAT and decreased specific GDP binding in both strains. Feeding a cafeteria diet resulted in obesity and increased mass and protein content of the IBAT in both strains of rats. However, specific GDP binding increased in response to cafeteria feeding only in the Osborne-Mendel rats. These studies show that thermogenesis, as measured by GDP binding to mitochondria in brown adipose tissue, is suppressed by both isoenergetic and ad libitum feeding of a high-fat diet. The higher basal GDP binding in the brown fat of the S 5B/Pl rats suggests that higher thermogenesis of this tissue contributes to the resistance of this strain to fat-induced obesity. The inability of S 5B/Pl rats to further increase thermogenesis when eating a cafeteria diet may contribute to their becoming obese.

Gastric bypass with biliopancreatic diversion

Gastric bypass with biliopancreatic diversion (GBBPD) is a combined restrictive and malabsorptive procedure for the treatment of morbid obesity.

Diet, lighting, and food intake affect norepinephrine turnover in dietary obesity

The effects of dietary fat content, lighting cycle, and feeding time on norepinephrine turnover in interscapular brown adipose tissue, heart, and pancreas, and on blood 3-hydroxybutyrate, serum glucose, insulin, and corticosterone have been studied in two strains of rats that differ in their susceptibility to dietary obesity. S 5B/Pl rats, which are resistant to dietary obesity, have a more rapid turnover of norepinephrine in interscapular brown adipose tissue and heart and a greater increase in the concentration of norepinephrine in brown fat when eating a high-fat diet than do Osborne-Mendel rats, which are sensitive to fat-induced obesity. Light cycle and feeding schedule are important modulators of sympathetic activity in heart and pancreas but not in brown fat. Rats of the resistant strain also have higher blood 3-hydroxybutyrate concentrations and lower insulin and corticosterone levels than do rats of the susceptible strain. A high-fat diet increases 3-hydroxybutyrate concentrations and reduces insulin levels in both strains. These studies show, in rats eating a high-fat diet, that differences in norepinephrine turnover, particularly in brown adipose tissue, may play an important role in whether dietary obesity develops and in the manifestations of resistance to this phenomenon observed in the S 5B/Pl rat.

Muscle creatine content in rats given repeated large doses of nicotinamide: effects of dietary methionine, choline, carnitine, and other supplements

Rats fed a 12% casein diet without added choline were chronically injected with pharmacologic doses of nicotinamide (NAM) for 18 to 28 d in three experiments. In addition to fatty livers and lower weight gains, the creatine content of heart and skeletal muscle was lower in NAM-treated than in control saline-injected rats. Dietary supplements of methionine prevented these alterations, and choline, depending on the level of supplementation, also had some similar effects. No consistent responses could be demonstrated by supplements of carnitine, histidine or folic acid plus vitamin B-12.

Zinc and copper nutriture in obese men receiving very low calorie diets of soy or collagen protein

Balance studies for Zn and Cu were conducted over 40 days in 10 obese men housed in a metabolic balance unit. Two weight reduction diets providing 400 kcal and 100 g protein daily were administered; to five subjects, a collagen diet which was severely deficient in both Zn and Cu, and to another five subjects, a soy diet which provided a marginal intake of Zn and an adequate intake of Cu. Zn and Cu content of diets, plasma, red blood cells, urine, and feces were determined during eight 5-day periods. Balances were corrected for lean tissue catabolism or deposition. Holter ECG monitoring and measurement of the QTc interval were done on days 0 and 40. Both diets resulted in elevated plasma and red blood cell concentrations of Zn and Cu and in high urinary and fecal losses of Zn. By day 40, 6 of 10 subjects were in negative Zn balance. Urinary Zn was inversely correlated with measures of lean tissue catabolism. During each period, Cu balance was markedly positive in the soy-diet group and negative in the collagen-diet group. Shortening of prolonged QTc intervals was related to the Cu but not Zn status of the individual.

Dietary obesity: effects of drugs on food intake in S 5B/P1 and Osborne-Mendel rats

The effect of several drugs on food intake has been examined in two strains of rats, one (S 5B/P1) which is resistant to developing obesity when eating a high fat diet, and one (Osborne-Mendel) which readily develops obesity when eating the same diet. Insulin and 2-deoxy-D-glucose increased food intake in a dose dependent manner in both S 5B/P1 and Osborne-Mendel rats. However, the S 5B/P1 rats showed a greater response, with a shorter latency period, to both agents than did the Osborne-Mendel rats. Conversely, d-amphetamine at the higher doses produced a dose dependent suppression of food intake with maximal suppression being similar for both strains. At a lower dose, however, d-amphetamine significantly increased food intake in the Osborne-Mendel rats, but not in the S 5B/P1 rats. The S 5B/P1 rats were also slightly more sensitive to the anorexic effects of lower dose adenosine than were the Osborne-Mendel rats whereas the reverse was true following higher dose adenosine. Naloxone suppressed food intake equally in both strains and D-glucose did not alter food intake in either strain. These studies identify three drugs, all stimulatory, to which the two strains of rat respond differently.

Metabolic and hormonal factors as predictors of nitrogen retention in obese men consuming very low calorie diets

The ability to conserve body protein during very low calorie diets in ten obese men was observed to correlate with plasma free amino acid concentrations, urinary N tau-methylhistidine: creatinine ratios, resting oxygen consumption, and serum triiodothyronine levels. A diet consisting of only protein, 1.3 g/kg ideal body weight/24 h, was given for 40 days. Cumulative nitrogen deficit ranged from -64 g to -227 g. Nitrogen balance on days 36 to 40 ranged from + 1.37 g/24 h to -3.30 g/24h. Nitrogen balance during this period had a significant direct correlation with pre-diet concentrations of branched-chain amino acids (r = 0.69 to 0.89), methionine (r = 0.85), histidine (r = 0.66), alanine (r = 0.73), arginine (r = 0.70), ornithine (r = 0.66), total essential (r = 0.87, and nonessential (r = 0.68) amino acids, with initial serum levels of triiodothyronine (r = 0.66) and with the fall in triiodothyronine over the 40 days (r = 0.79). Initial resting oxygen consumption was directly correlated (r = 0.78) with final nitrogen balance and inversely with total nitrogen loss (r = -0.81). On day 0, triiodothyronine levels also correlated positively (r ranging from 0.71 to 0.93) with plasma concentrations of several essential and nonessential amino acids. These correlations suggest that individuals who ultimately will or will not achieve nitrogen equilibrium during very low calorie diets can be identified prior to dieting. These data are consistent with the hypothesis that individuals with higher initial protein flux and triiodothyronine levels are better able to adjust the balance between synthesis and degradation to attain nitrogen equilibrium during hypocaloric dieting.

Relationship between the changes in serum thyroid hormone levels and protein status during prolonged protein supplemented caloric deprivation

The relationship between the changes in serum thyroid hormone levels and nitrogen economy during caloric deprivation were investigated in ten obese men during a 40 d, 400 kcal protein-supplemented weight-reducing diet. This regimen induced increases in the serum levels of total T4, free T4 and total rT3, and decreases of total T3, while serum TSH remained unchanged. There were progressive decreases in total body weight and urinary losses of total nitrogen and 3-methylhistidine, with the early negative nitrogen balance gradually returning towards basal values during the 40 days. Subjects with the largest weight loss had the most increase in the serum levels of total T4 and free T4 index and the greatest decrease in T3. The magnitude of the increase of the nitrogen balance from its nadir was correlated with the extent of the reduction of T3 and increase of T3 uptake ratio and free T4 levels. The decrease in the urinary excretion of 3-methylhistidine correlated with the increase in free T4 and rT3 levels. Nadir serum transferrin values were directly related to peak rT3 values, and the lowest albumin concentrations occurred in subjects with the highest total T4 and free T4 index values. Further, the maximum changes in the serum thyroid hormone levels preceded those of the nutritional parameters. These relationships suggest that: (1) increases in serum rT3 and free T4 and reductions in T3 concentrations during protein supplemented weight reduction may facilitate conservation of visceral protein and reduce muscle protein turnover; and (2) the variation in the magnitude of these changes may account for the heterogeneity of nitrogen economy.

Plasma concentration of amino acids in obese men consuming very-low-calorie diets composed of soy or collagen protein

The effects of soy or collagen protein, 1.3 g/kg desirable body weight per day, on fasting and postprandial plasma free amino acid concentrations were evaluated in eight obese men during a 40-day very-low-calorie reducing regimen. The interrelationships among individual plasma amino acids were also examined. In both protein-fed groups, fasting plasma histidine, phenylalanine, tyrosine, threonine and alanine levels decreased by day 40 whereas glycine increased. The decrease in plasma threonine and increase in plasma glycine were more pronounced in the collagen-fed group (n = 4) than in the soy-fed group (n = 4). Serine increased only in the collagen-fed group. The postprandial increases of all essential amino acids, with the exception of valine and phenylalanine, were less on day 26 than on day zero. Except for threonine levels, plasma amino acid profiles were similar during very-low-calorie dieting and during prolonged fasting. However, essential amino acid levels were better maintained by soy than by collagen protein diets.

Catecholamine turnover in S 5B/P1 and Osborne-Mendel rats: response to a high-fat diet

Catecholamine turnover in response to fasting, cold exposure, and a high-fat diet has been measured in the Osborne-Mendel rat, which readily develops obesity when fed a high-fat diet, and the S 5B/P1 rat, which does not. We have tested the hypothesis that this difference in response to diet might be associated with altered rates of norepinephrine or epinephrine turnover. The endogenous norepinephrine concentration in interscapular brown adipose tissue was significantly greater in fasted S 5B/P1 rats than in fasted Osborne-Mendel rats. The fractional norepinephrine turnover rate in interscapular brown adipose tissue of fasted animals was also greater in the S 5B/P1 rat than in the Osborne-Mendel rat. Cold exposure increased the fractional norepinephrine turnover rate in interscapular brown adipose tissue for both strains of rats but increased the fractional norepinephrine turnover rate in the pancreas in only the Osborne-Mendel rats. The turnover of epinephrine and the adrenal concentration of this hormone were not different between the two strains. Normal and high-fat diets were fed to both strains; the Osborne-Mendel rats were pair fed the high-fat diet to prevent excess weight gain. Endogenous concentrations of norepinephrine in interscapular brown adipose tissue was increased by the high-fat diet; the increase was greater in S 5B/P1 rats. The high-fat diet resulted in increased norepinephrine turnover in interscapular brown adipose tissue of the S 5B/P1 rat but not the Osborne-Mendel rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium, magnesium, and phosphate balances during very low calorie diets of soy or collagen protein in obese men: comparison to total fasting

In 30 obese men, calcium, magnesium, and phosphate balances were measured for 40 days using one of four weight reducing regimens: 1) 400 kcal soy protein; 2) 400 kcal collagen protein; 3) total fasting with potassium; and 4) total fasting without potassium. Relationship of the minerals to each other and to nitrogen and to the QTc interval was also examined. All groups were in negative cumulative calcium balance but the protein-fed groups lost less calcium (soy, -3.0 +/- 2.1 g; collagen -4.9 +/- 3.2 g) than the total fasting groups (with potassium supplement, -9.2 +/- 3.4 g; without potassium supplement, -5.8 +/- 2.1 g) (p less than 0.01). The soy-fed group attained positive cumulative magnesium (0.7 +/- 0.5 g) and phosphate balances (6.9 +/- 3.9 g). The other three groups had significantly more negative magnesium (p less than 0.0005) and phosphate (p less than 0.0005) balances, (collagen, magnesium balance, -1.1 +/- 1.0 g, and phosphate balance, -7.6 +/- 3.7 g; total fasting without potassium, magnesium balance, -1.4 +/- 0.6 g, and phosphate balance, -5.4 +/- 2.7 g). Potassium supplementation during fasting increased urinary losses of calcium and fecal losses of magnesium. High phosphate intake reduced urinary calcium. Nitrogen losses predicted only magnesium losses. Serum mineral levels did not reflect tissue mineral status. Shortening in the QTc interval as an indicator of reduced myocardial instability was related to the increase in serum phosphate in the protein-fed subjects.

Ventromedial hypothalamic knife-cut lesions in rats resistant to dietary obesity

The effects of ventromedial hypothalamic (VMH) knife-cut lesions on food intake and body weight of S 5B/Pl rats, which are normally resistant to obesity when eating a high-fat diet, were examined in two experiments. In the first experiment body weight increased only slightly after VMH knife-cut lesions when animals were fed pelleted laboratory chow or a 10% corn oil diet. When eating the 30% corn oil diet, however, body weight increased in the VMH knife-cut rats. In the second experiment VMH knife-cut lesions produced a small weight gain in rats fed the 10% fat diet; this manipulation also increased food intake and disrupted the normal diurnal feeding pattern. Changes in the weight of the liver, interscapular brown adipose tissue, and white adipose tissue paralleled the changes in body weight. Plasma insulin increased in the rats eating the 30% corn oil diet ad libitum but not in the VMH-lesioned animals pair fed to the sham-operated rats. Incorporation of 3H from 3H2O into lipid was significantly increased in white fat of animals with VMH knife cuts. Similar results were obtained from incubation of adipose tissue in vitro with insulin and radioactively labeled glucose. These studies show that hypothalamic knife-cut lesions can remove the resistance of the S 5B/Pl rats to obesity when they are fed a high-fat diet.

Effects of oral and parenteral quinine on rats with ventromedial hypothalamic knife-cut obesity

The addition of quinine to the food reversed the obesity in rats with hypothalamic hyperphagia induced by knife cuts. Similarly, the injection of quinine into rats with hypothalamic knife cuts reduced food intake and body weight but the effects were smaller than those observed when quinine was added to the diet. Urinary quinine excretion was similar by the oral and parenteral routes. The food intake of the knife-cut animals receiving quinine gradually fell to the same level as in the sham-operated animals receiving quinine by either route. The weights of retroperitoneal fat pads were related to the weights of the animals and were reduced in the quinine-treated groups. Plasma insulin concentrations were significantly higher in the knife-cut animals and were reduced toward control levels by quinine treatment. Gluconeogenesis, measured by incorporation of radioactivity from labeled bicarbonate into glucose, was unaffected by treatment with quinine or by knife cuts. Lipogenesis from tritiated water in vivo was not different between treatment groups in the liver or retroperitoneal fat pads. However, in vivo lipogenesis was reduced in knife-cut rats fed ad libitum compared with quinine-treated rats. The response of lipogenesis to insulin in vitro was also not different between treatment groups. These data suggest that a major part of the reduction in food intake in hyperphagic rats eating a quinine-adulterated diet is due to postingestional events.

Nitrogen economy during very low calorie reducing diets: quality and quantity of dietary protein

Controversy exists whether protein quantity or quality affect "nitrogen sparing" or physical health while subsisting on very low calorie diets. Therefore, in 38 obese men, nitrogen economy was evaluated over 2 months periods using one of five regimens: 1) 400 kcal high quality protein: 2) 400 kcal low quality protein; 3) 500 kcal 55 g protein natural food; 4) total fasting with potassium; and 5) total fasting without potassium. Up to the 20- and 40-day intervals, mean cumulative nitrogen deficity for all three diet groups was the same but 60% lower than with total fasting. However, within groups, individual capability to conserve nitrogen varied over as much as 2.8-fold. All 10 subjects of diet groups 1 and 2 had negative nitrogen balances to day 21, and six of these subjects were still negative by day 40. The improvement in nitrogen conservation and the ability to attain nitrogen equilibrium was unrelated to the differences in protein quantity and quality. Intake of essential or branched-chain amino acids was also unrelated to the efficiency of nitrogen conservation, as were insulin, glucagon, and 3-hydroxybutyrate levels. The only indicator correlating positively with nitrogen deficit was a fall in complement C3 (r = 0.87). Despite the extent of overall nitrogen loss, no cardiac arrhythmias were observed with either the high or low quality protein diet.