Central Exendin‐4 Infusion Reduces Body Weight without Altering Plasma Leptin in (fa/fa) Zucker Rats

Objective: To investigate whether chronic administration of the long‐acting glucagon‐like peptide‐1 receptor agonist exendin‐4 can elicit sustained reductions in food intake and body weight and whether its actions require an intact leptin system. Research Methods and Procedures: Male lean and obese Zucker (fa/fa) rats were infused intracerebroventricularly with exendin‐4 using osmotic minipumps for 8 days. Results: Exendin‐4 reduced body weight in both lean and obese Zucker rats, maximum suppression being reached on Day 5 in obese (8%) and Day 7 in lean (16%) rats. However, epididymal white adipose tissue weight was not reduced, and only in lean rats was there a reduction in plasma leptin concentration. Food intake was maximally suppressed (by 81%) on Day 3 in obese rats but was reduced by only 18% on Day 8. Similarly, in lean rats food intake was maximally reduced (by 93%) on Day 4 of treatment and by 45% on Day 8. Brown adipose tissue temperature was reduced from Days 2 to 4. Plasma corticosterone was elevated by 76% in lean but by only 28% in obese rats. Discussion: Chronic exendin‐4 treatment reduced body weight in both obese and lean Zucker rats by reducing food intake: metabolic rate was apparently suppressed. These effects did not require an intact leptin system. Neither does the absence of an intact leptin system sensitize animals to exendin‐4. Partial tolerance to the anorectic effect of exendin‐4 in lean rats may have been due to elevated plasma corticosterone and depressed plasma leptin levels, but other counter‐regulatory mechanisms seem to play a role in obese Zucker rats.     

Increase of neuronal histamine in obese rats is associated with decreases in body weight and plasma triglycerides

Objective: The purpose of the present study was to examine the metabolic effects of a specific histamine H₃ receptor antagonist, the cinnamic amide NNC 0038‐0000‐1202 (NNC 38‐1202). Research Methods and Procedures: Effects of NNC 38‐1202 on paraventricular levels of histamine and acute effects on food intake were followed in normal rats, whereas effects on body weight homeostasis and lipid metabolism were studied in a rat model of diet‐induced obesity (DIO). Results: NNC 38‐1202, administered as single oral doses of 15 and 30 mg/kg, significantly (p < 0.01) increased paraventricular histamine by 339 ± 54% and 403 ± 105%, respectively, compared with basal levels. The same doses produced significant (p < 0.01) reductions in food intake. In DIO rats receiving NNC 38‐1202 in a daily dose of 5 mg/kg for 22 days, a decrease in food intake was associated with a significant (p < 0.001) net loss of body weight (?11.0 ± 4.8 grams), compared with rats receiving vehicle, which gained 13.6 ± 3.0 grams. Also, NNC 38‐1202 significantly (p < 0.05) reduced plasma triglycerides by ～42%, in parallel with increases in plasma free fatty acids and β‐hydroxybutyrate levels. Despite reductions in food intake and body weight following administration of NNC 38‐1202, no sign of a decrease in energy expenditure was observed, and whole‐body lipid oxidation was significantly (p < 0.05) increased in the period after dosing. Discussion: The present study suggests that antagonistic targeting of the histamine H₃ receptor decreases food intake, body weight, and plasma TG levels and, thus, represents an interesting approach to treatment of obesity and associated hyperlipidemia.     

Intracerebroventricular Glucocorticoid Infusion in Normal Rats: Induction of Parasympathetic‐Mediated Obesity and Insulin Resistance

Objective: The aims of the present study were to determine whether increased body weight resulting from intracerebroventricular (ICV) glucocorticoid (dexamethasone) infusion in normal rats is associated, as in obesity, with changes in glucose metabolism and to investigate whether the parasympathetic nervous system is involved in the glucocorticoid‐induced effects. Research Methods and Procedures: Male Sprague–Dawley rats were infused with ICV dexamethasone (2.5 μg/d) or its vehicle for 2 days during which food intake, body weight, and basal insulinemia were measured. Euglycemic–hyperinsulinemic clamps associated with the labeled 2‐deoxyglucose technique were then performed to determine the total rate of glucose disappearance and the tissue glucose use indices. Similar experiments were carried out in vagotomized rats. Results: Two days of ICV glucocorticoid infusion in normal rats resulted in increases in food intake, body weight, basal insulinemia, and produced decreases in the insulin‐stimulated total rate of glucose disappearance, as well as in glucose use indices of all muscle types studied. None of these alterations was observed when glucocorticoid infusion was carried out in vagotomized rats. Discussion: These data show that central glucocorticoid infusion favors anabolic processes, such as feeding behavior, body weight gain, and insulin output, while promoting muscle insulin resistance. These effects seem to be mediated by an activation of the parasympathetic nervous system, because they all disappear when tested in vagotomized rats.     

The Rat Corpulent (cp) Mutation Maps to the Same Interval on (Pgm1-Glut1) Rat Chromosome 5 as the Fatty (fa) Mutation

The autosomal recessive obesity mutations fatty (fa) and corpulent (cp) arose in separate rat strains, 13M and Koletsky, respectively. By complementation analysis, the two mutations appear to be in the same gene. The somewhat different phenotypes of fa/fa and cp/cp animals probably reflect the fact that the mutations are segregating on different rat strains. The fa mutation has been mapped to the interval between Pgm1 and Glut1 on rat Chr 5, but cp has not been mapped genetically. We mapped cp in 30 obese progeny of a LA/N-BN cp/+ intercross using microsatellite markers for these flanking genes. Cp maps to the same genetic interval as rat fa and mouse db. Cp is flanked by Glut1 and Pgm1: Pgm1——–cp——–Glut1 map distance (cM) 1.67 6.67 Thus, cp and fa map to the same ～8 cM interval of the rat genome. In conjunction with the complementation studies alluded to above, these findings indicate that cp and fa are mutations in the same gene (Lepr).     

S 23521 Decreases Food Intake and Body Weight Gain in Diet‐Induced Obese Rats

Objective: To investigate the effect of S 23521, a new glucagon‐like peptide‐1‐(7‐36) amide analogue, on food intake and body weight gain in obese rats, as well as on gene expression of several proteins involved in energy homeostasis. Research Methods and Procedures: Lean and diet‐induced obese rats were treated with either S 23521 or vehicle. S 23521 was given either intraperitoneally (10 or 100 μg/kg) or subcutaneously (100 μg/kg) for 14 and 20 days, respectively. Because the low‐dose treatment did not affect food intake and body weight, the subcutaneous treatment at high dose was selected to test the effect on selected end‐points. Results: Treated obese rats significantly decreased their cumulative energy intake in relation to vehicle‐treated counterparts (3401 ± 65 vs. 3898 ± 72 kcal/kg per 20 days; p < 0.05). Moreover, their body weight gain was reduced by 110%, adiposity was reduced by 20%, and plasma triglyceride levels were reduced by 38%. The treatment also improved glucose tolerance and insulin sensitivity of obese rats. Regarding gene expression, no changes in uncoupling protein‐1, uncoupling protein‐3, leptin, resistin, and peroxisome proliferator‐activated receptor (PPAR)‐γ were observed. Discussion: S 23521 is an effective glucagon‐like peptide‐1‐(7‐36) amide analogue, which induced a decrease in energy intake, body weight, and adiposity in a rat model of diet‐induced obesity. In addition, the treatment also improved glucose tolerance and insulin sensitivity of obese rats. These results strongly support S 23521 as a putative molecule for the treatment of obesity.     

Utility of a C-Jun Microsatellite Marker in Determining Gene Dosage for fatty (fa)

The Zucker fatty (fa) mutation provides a genetic model for obesity and non-insulin dependent diabetes mellitus. The molecular pathogenesis of the metabolic phenotype of these animals is not known. Detailed molecular maps of the region surrounding the fa locus on rat chromosome 5 can be used for positional cloning experiments as well as to permit genotyping of animals from appropriate crosses before the confounding metabolic effects of obesity have occurred. We describe the development of a polymerase chain reaction (PCR) assay for a polymorphic simple sequence repeat (SSR) in the promoter region of the protooncogene c-Jun. This assay was used to position cJun 4.5cM proximal to the fa locus in 111 F2 progeny of a 13MBN fa/+ F1 intercross. Concurrent use of the cJun SSR with a previously described assay for a microsatellite in the glucose transporter, Glutl, permits rapid and accurate assessment of genotypes at the fa locus in animals of any age using minimal amounts of DNA. A strategy is described which minimizes the error rate in assigning genotype at the fatty locus for backcross and intercross progeny.     

Abnormal immune responses in fa/fa Zucker rats and effects of feeding conjugated linoleic acid

Objective: The objective of this study was to characterize immune function in the fa/fa Zucker rat, and to determine the effects of feeding conjugated linoleic acid (CLA) isomers on immune function. Methods and Procedures: Lean and fa/fa Zucker rats were fed for 8 weeks nutritionally complete diets with different CLA isomers (%wt/wt): control (0%), c9t11 (0.4%), t10c12 (0.4%), or MIX (0.4% c9t11 + 0.4% t10c12). Isolated splenocytes were used to determine phospholipid (PL) fatty acid composition and cell phenotypes, or stimulated with mitogen to determine their ability to produce cytokines, immunoglobulins (Ig), and nitric oxide (NO). Results: Splenocyte PL of fa/fa rats had a higher proportion of total monounsaturated fatty acids and n ?3 polyunsaturated fatty acids (PUFA), and lower n ?6 PUFA and n ?6‐to‐n ?3 PUFA ratio (P < 0.05). Feeding CLA increased the content of CLA isomers into PL, but there were lower proportions of each CLA isomer in fa/fa rats. Splenocytes of fa/fa rats produced more amounts of IgA, IgG, and IgM, NO, and interleukin‐1β (IL‐1β), IL‐6, and tumor necrosis factor‐α (TNF‐α) (P < 0.05). Obese rats fed the t10c12 diet produced less TNF‐α and IL‐1β (lippopolysaccharide (LPS), P < 0.05). Splenocytes of fa/fa rats produced less concanavalin A (ConA)‐stimulated IL‐2 (P < 0.0001) than lean rats, except fa/fa rats fed the c9t11 diet (P < 0.05). Discussion: The c9t11 and t10c12 CLA isomers were incorporated into the membrane PL of the fa/fa Zucker rat, but to a lesser extent than lean rats. Splenocytes of obese rats responded in a proinflammatory manner and had reduced T‐cell function and feeding the t10c12 and c9t11 CLA isomers may improve some of these abnormalities by distinct methods.     

Effects of Exendin‐4 Alone and With Peptide YY3–36 on Food Intake and Body Weight in Diet‐Induced Obese Rats

Significant weight loss following Roux‐en‐Y gastric bypass surgery (RYGB) in obese humans correlates with enhanced secretion of anorexigenic gut hormones glucagon‐like peptide‐1 (GLP‐1) and peptide YY_3–36 (PYY_3–36). Our aim here was to identify a dosing strategy for intraperitoneal (IP) infusion of GLP‐1 homologue exendin‐4 alone and with PYY_3–36 that produces a sustained reduction in daily food intake and body weight in diet‐induced obese (DIO) rats. We tested 12 exendin‐4 strategies over 10 weeks. Exendin‐4 infused during the first and last 3 h of the dark period at 15–20 pmol/h (0.15 nmol/kg/day) produced a sustained 24 ± 1% reduction in daily food intake for 17 days, and decreased body weight by 7%. In a separate group of DIO rats, none of seven dosing strategies combining exendin‐4 and PYY_3–36 produced a similar reduction in daily food intake for >10 days. The subsequent decline in efficacies of exendin‐4 alone and with PYY_3–36 on food intake and body weight in each experiment suggested possible receptor downregulation and tolerance to treatments. However, when treatments were discontinued for 1 day following losses in efficacies, daily food intake significantly increased. Together, these results demonstrate that (i) intermittent IP infusion of a low dose of exendin‐4 can produce a relatively prolonged reduction in daily food intake and body weight in DIO rats, (ii) co‐infusion of exendin‐4 and PYY_3–36 does not further prolong this response, and (iii) activation of an orexigenic mechanism gradually occurs to counteract the inhibitory effects of exendin‐4 alone and with PYY_3–36 on food intake and body weight.     

The Effects of Leptin Administration in Non‐obese Human Subjects

Objective: Body fatness is partly under hypothalamic control with effector limbs that include the endocrine system and the autonomic nervous system (ANS). In previous studies of both obese and never‐obese subjects, we have shown that weight increase leads to increased sympathetic and decreased parasympathetic activity, whereas weight decrease leads to decreased sympathetic and increased parasympathetic activity. We now report on the effect of leptin, independent of weight change, on the ANS. Research Methods and Procedures: Normal weight males (ages 20–40 years) were fed a solid food diet, measured carefully to maintain body weight, for 3 weeks, as inpatients at the Rockefeller University General Clinical Research Center. In a single‐blind, 22‐day, placebo/drug/placebo design, six subjects received leptin 0.3 mg/kilogram subcutaneously for 6 days. ANS measures of amount of parasympathetic control and sympathetic control of heart period (interbeat interval) were made by sequential pharmacological blockade with intravenous atropine and esmolol. Norepinephrine, dopamine, and epinephrine levels in 24‐hour urine collections were also measured as well as resting metabolic rate. Results: Sufficient food intake maintained constant body weight in all subjects. There was no evidence that leptin administration led to changes in energy metabolism sufficient to require additional food intake or to alter resting metabolic rate. Likewise, leptin administration did not alter autonomic activity. Parasympathetic control and sympathetic control, as well as the urinary catecholamines, were not significantly affected by leptin administration. Glucose and insulin levels were increased by food intake as expected, but leptin had no affect on these levels before or after food intake. Discussion: ANS responses to changes in energy metabolism found when food intake and body weight are altered were not found in these never‐obese subjects given leptin for 6 days. Although exogenous leptin administration has profound effects on food intake and energy metabolism in animals genetically deprived of leptin, we found it to have no demonstrable effect on energy metabolism in never‐obese humans. The effects of longer periods of administration to obese individuals and to those who have lost weight demand additional investigation.     

Subdiaphragmatic vagal deafferentation affects body weight gain and glucose metabolism in obese male Zucker (fa/fa) rats

We investigated the effect of subdiaphragmatic vagal deafferentation (SDA) on food intake, body weight gain, and metabolism in obese (fa/fa) and lean (Fa/?) Zucker rats. Before and after recovery from surgery, food intake and body weight gain were recorded, and plasma glucose and insulin were measured in tail-prick blood samples. After implantation of a jugular vein catheter, an intravenous glucose tolerance test (IVGTT) was performed, followed by minimal modeling to estimate the insulin sensitivity index. Food intake relative to metabolic body weight (g/kg(0.75)) and daily body weight gain after surgery were lower (P < 0.05) in SDA than in sham obese but not lean rats. Before surgery, plasma glucose and insulin concentrations were lower (P < 0.05) in lean than in obese rats but did not differ between surgical groups within both genotypes. Four weeks after surgery, plasma glucose and insulin were still similar in SDA and sham lean rats but lower (P < 0.05) in SDA than in sham obese rats. IVGTT revealed a downward shift of the plasma insulin profile by SDA in obese but not lean rats, whereas the plasma glucose profile was unaffected. SDA decreased (P < 0.05) area under the curve for insulin but not glucose in obese rats. The insulin sensitivity index was higher in lean than in obese rats but was not affected by SDA in both genotypes. These results suggest that elimination of vagal afferent signals from the upper gut reduces food intake and body weight gain without affecting the insulin sensitivity index measured by minimal modeling in obese Zucker rats.     

Nutrient Specific Feeding and Endocrine Effects of Jejunal Infusions

Intestinal nutrient infusions result in variable decreases in food intake and body weight based on the nutrient type and the specific intestinal infusion site. Only intrajejunal infusions of fatty acids decrease food intake beyond the calories infused. To test whether this extra‐compensatory decrease in food intake is specific to fatty acids, small volume intrajejunal infusions of glucose (Glu) and casein hydrolysate (Cas), as well as linoleic acid (LA) were administered to male Sprague–Dawley rats. Equal kilocalorie (kcal) loads of these nutrients (11.4) or vehicle were infused into the jejunum over 7 h/day for five consecutive days. Food intake was continuously monitored and body weight was measured daily. After the infusion on the final day, rats were killed and plasma collected. Intrajejunal infusions of LA and Glu, but not Cas, suppressed food intake beyond the caloric load of the infusate with no compensatory increase in food intake after the infusion period. Rats receiving LA and Glu infusions also lost significant body weight across the infusion days. Plasma glucagon‐like peptide‐1 (GLP‐1) was increased in both the LA and Glu rats compared with control animals, with no significant change in the Cas‐infused animals. Peptide YY (PYY) levels increased in response to LA and Cas infusions. These results suggest that intrajejunal infusions of LA and Glu may decrease food intake and body weight via alterations in GLP‐1 signaling. Thus, particular nutrients are more effective at producing decreases in food intake, body weight, and inducing changes in peptide levels and could lead to a novel therapy for obesity.     

Effect of cerebrocrast on body and organ weights,food and water intake,and urine output of normal rats

Type 2 diabetes is associated with obesity, insulin resistance, hyperglycemia, hyperphagia, polyuria, body weight gain, excessive secretion of glucocorticoids (GCs), thymus involution, adrenal gland hypertrophy, diabetic nephropathy, etc. We examined the effect of cerebrocrast, a new antidiabetic agent (synthesized in the Latvian Institute of Organic Synthesis), on body weight, food and water intake, urine output, and on changes of organ weight: that is, kidney, thymus, adrenal gland of normal rats. Cerebrocrast was administered at doses of 0.05 and 0.5 mg kg⁻¹ per os (p.o.) once a day for three consecutive days, and its effects were observed from 3 to 27 days after the last administration. Cerebrocrast, during the experimental period, decreased body weight by an average of approximately 32.3%, food intake by about 10–15% at the beginning of the experiments and by 22.6% at the end of the experiments, especially at a dose of 0.5 mg kg⁻¹. Water intake and urine output in comparison with controls were decreased. The daily food intake decreased about 1.0 and 2.1 g by administering single cerebrocrast doses of 0.05 and 0.5 mg kg⁻¹ body weight (b.w.), respectively, but by administering for three consecutive days, food intake decreased by about 2.2 and 3.4 g, respectively. The weekly body weight gain decreased by administering a single dose of cerebrocrast by 2.61 and 2.51 g, respectively, and by triple administration it decreased by 4.36 and 3.07 g, respectively. Cerebrocrast has long‐lasting effects on these parameters and on thymus and adrenal gland weight. As cerebrocrast decreased glucose levels in normal and streptozotocin (STZ)‐induced diabetic rats, it also promoted glucose uptake by the brain, intensified insulin action and formation de novo of insulin receptors. We can conclude that cerebrocrast may regulate food intake and body weight through glucose sensing by proopiomelanocortin (POMC) neurons, that are involved in control of glucose homeostasis, stimulation of α‐melanocyte‐stimulating hormone (α‐MSH) secretion, activation of MC4‐Rs and inhibition of neuropeptide Y (NPY) in the ARC of the hypothalamus, affecting the kidney, and causing decreased urine output and water intake. Moreover, it could stimulate secretion of vasopressin. By administration of cerebrocrast thymus mass was increased, thereby preventing the action of GCs. As cerebrocrast inhibited L‐ and T‐type calcium channels, it can prevent vasoconstriction of kidney arterioles and aldosterone secretion that have significant roles in the development of hypertension and diabetic nephropathy. These properties of cerebrocrast are important for treatment of Type 2 diabetes and its consequent development of hypertension and diabetic nephropathy. Copyright © 2008 John Wiley & Sons, Ltd.     

Genetic map of rat Chromosome 5 including the fatty (fa) locus

Thirteen loci, including the obesity gene fatty (fa), were incorporated into a linkage map of rat Chromosome (Chr) 5. These loci were mapped in obese (fa/fa) progeny of a cross between BN×13M-fa/+ F₁ animals. Obese rats were scored for BN and 13M alleles at four loci (Ifna, D1S85h, C8b, and Lck1) by restriction fragment length polymorphisms and at eight additional loci (Glut1, Sv4j2, R251, R735, R980, R252, R371, and R1138) by simple sequence length polymorphisms (SSLP). The resulting map spans 67.3 cM of Chr 5, presenting nine previously unmapped loci and one locus (Lck1) previously assigned to Chr 5 by use of somatic cell hybrid lines. Seven of the eight SSLP loci are newly identified; the SSLP linkage group alone spans 56.8 cM. The order of the loci is Sv4j2-R251-R735-R980-R1138-Ifna-fa-D1S85h-C8b-(Glut1-R252-R371)-Lck1. One locus, D1S85h, was found to lie only 0.4 cM from fa, close enough to serve as a reliable marker for the prediction of phenotype from genotype, and will be useful also for studies on the development of obesity in the fatty rat.     

Bingeing,Self‐restriction,and Increased Body Weight in Rats With Limited Access to a Sweet‐fat Diet

Objective: Prior research has shown that fasting alternated with a diet of standard rodent chow and a 10% sucrose solution produces bingeing on the sucrose, but animals remain at normal body weight. The present study investigated whether restricted access to a highly palatable combination of sugar and fat, without food deprivation, would instigate binge eating and also increase body weight. Methods and Procedures: Male rats were maintained for 25 days on one of four diets: (i) sweet‐fat chow for 2 h/day followed by ad libitum standard chow, (ii) 2‐h sweet‐fat chow only 3 days/week and access to standard chow the rest of the time, (iii) ad libitum sweet‐fat chow, or (iv) ad libitum standard chow. Results: Both groups with 2‐h access to the sweet‐fat chow exhibited bingeing behavior, as defined by excessively large meals. The body weight of these animals increased due to large meals and then decreased between binges as a result of self‐restricted intake of standard chow following binges. However, despite these fluctuations in body weight, the group with 2‐h access to sweet‐fat chow every day gained significantly more weight than the control group with standard chow available ad libitum. Discussion: These findings may have implications for the body weight fluctuations associated with binge‐eating disorder, as well as the relationship between binge eating and the obesity epidemic.