Calorimetric measurements made on rats during repeated periods of weight gain and weight loss

Characterization of the 5-HT2C receptor agonist lorcaserin on efficacy and safety measures in a rat model of diet-induced obesity

The 5-HT2C receptor agonist lorcaserin (Belviq®) has been Food and Drug Administration (FDA) approved for the treatment of obesity. The present study is a back translational investigation into the effect of 28-day lorcaserin treatment in a diet-induced obesity (DIO) model using male, Sprague-Dawley rats. An assessment of drug effect on efficacy and multiple safety endpoints including cardiac function was undertaken. Lorcaserin (1-2 mg/kg SC b.i.d.) significantly reduced percentage body weight gain compared to vehicle-treated controls (VEH: 10.6 ± 0.4%; LOR 1: 7.6 ± 1.2%; LOR 2: 5.4 ± 0.6%). Measurement of body composition using quantitative magnetic resonance (QMR) imaging indicated this change was due to the selective reduction in body fat mass. Modest effects on food intake were recorded. At the completion of the treatment phase, echocardiography revealed no evidence for valvulopathy, that is, no aortic or mitral valve regurgitation. The pharmacokinetics of the present treatment regimen was determined over a 7-day treatment period; plasma C min and C max were in the range 13-160 ng/mL (1 mg/kg b.i.d.) and 34-264 ng/mL (2 mg/kg b.i.d.) with no evidence for drug accumulation. In sum, these studies show an effect of lorcaserin in the DIO model, that in the context of the primary endpoint measure of % body weight change was similar to that reported clinically (i.e., 3.0-5.2% vs. 3.2%). The present studies highlight the translational value of obesity models such as DIO, and suggest that assuming consideration is paid to nonspecific drug effects such as malaise, the DIO model has reasonable forward translational value to help predict clinical outcomes of a new chemical entity.

The cannabinoid CB1 receptor inverse agonist, rimonabant, modifies body weight and adiponectin function in diet-induced obese rats as a consequence of reduced food intake

The cannabinoid CB1 receptor inverse agonist rimonabant induces hypophagia and body weight loss. Reduced body weight may potentially be due to decreased food intake or to direct metabolic effects of drug administration on energy expenditure. This study uses a paired-feeding protocol to quantify the contributions of energy intake to rimonabant-induced body weight loss. Diet-induced obese (DIO) rats were dosed with rimonabant (3, 10 mg/kg PO once daily) and matched with pair-fed controls. Food intake and body weight were measured daily. Blood samples and adipose tissue were collected on day 15 for measurement of plasma adiponectin and adiponectin mRNA levels. DIO rats treated with rimonabant and pair-fed controls showed very similar changes in body weight. Although tolerance developed to the anorectic effect of rimonabant, total food intake was significantly decreased over the 14-day study period and fully accounted for the observed reductions in body weight. Adiponectin mRNA and plasma adiponectin were elevated in vehicle-treated chow-fed animals compared to obese controls, and did not differ between rimonabant-treated and pair-fed animals. The similarities between rimonabant-treated and pair-fed animals in body weight loss and the absence of differences in measures of adiponectin activity between drug-treated and pair-fed animals suggest that the outcomes of this experiment were solely mediated by the drug-induced reduction in food intake.

Effects of the biliopancreatic diversion on energy balance in the rat

OBJECTIVE

This study was carried out to determine the effects of the biliopancreatic diversion (BPD), a bariatric surgery applied to the treatment of morbidly obese humans, on energy balance in rats.

METHODS

BPD was performed on a group of male Wistar rats. Body weight and food intake were measured daily throughout the study. Feces were also collected to assess energy losses and the determination of digestible energy. Energy expenditure and body composition were also determined for the 50-day length of the protocol. On the day of killing, the brain, the entire intestinal tract and white and brown adipose tissues were collected and weighed. Expression of neuropeptide Y (NPY) and agouti-related protein (AgRP) in the ARC nucleus were assessed by in situ hybridization.

RESULTS

Marked changes in the regulation of energy balance were observed in the BPD-operated rats. A decrease in digestible energy and food intake coupled with an increase in the fecal energy density and protein fecal energy led to an important weight loss in the BPD-operated rats. This weight loss was observed in the loss of fat mass (specifically the white epididymal, inguinal, retroperitoneal and brown adipose tissues). The rats modified their food intake pattern to be able to potentially eat more during the entire day. An increase in the surfaces of all intestinal structures (muscular and mucosal layers) was observed in the BPD-operated rats. The NPY and AgRP expression in the brain were both shown to be greater in the BPD-operated rats than in the control animals. At the beginning of the study, the surgery led to an energy expenditure decrease, which, however, did not persist throughout the study despite the fact that BPD-operated rats exhibited persistent lower fat free masses.

CONCLUSION

BPD led to a noticeable reduction in weight and fat gains in rats, which was in large part owing to a decrease in digestible energy intake led to by the gastrectomy, the intestinal malabsorption inherent to the surgery and to potentially a thermogenesis stimulation that occurred in the second end of the study. The reduction in energy gain occurs despite adaptations to thwart the intestinal malabsorption and the hunger signals from the central nervous system.

Effect of photoperiod on body mass, food intake and body composition in the field vole, Microtus agrestis

Many small mammals respond to seasonal changes in photoperiod by altering body mass and adiposity. These animals may provide valuable models for understanding the regulation of energy balance. Here, we present data on the field vole (Microtus agrestis) - a previously uncharacterised example of photoperiod-induced changes in body mass. We examined the effect of increased day length on body mass, food intake, apparent digestive efficiency, body composition, de novo lipogenesis and fatty acid composition of adipose tissue in cold-acclimated (8 degrees C) male field voles by transferring them from a short (SD, 8 h:16 h L:D) to long day photoperiod (LD, 16 h:8 h L:D). During the first 4 weeks of exposure to LD, voles underwent a substantial increase in body mass, after which the average difference between body masses of LD and SD voles stabilized at 7.5 g. This 24.8% increase in body mass reflected significant increases in absolute amounts of all body components, including dry fat mass, dry lean mass and body water mass. After correcting body composition and organ morphology data for the differences in body mass, only gonads (testes and seminal vesicles) were enlarged due to photoperiod treatment. To meet energetic demands of deposition and maintenance of extra tissue, voles adjusted their food intake to an increasing body mass and improved their apparent digestive efficiency. Consequently, although mass-corrected food intake did not differ between the photoperiod groups, the LD voles undergoing body mass increase assimilated on average 8.4 kJ day(-1) more than animals maintained in SD. The majority (73-77%) of the fat accumulated as adipose tissue had dietary origin. The rate of de novo lipogenesis and fatty acid composition of adipose tissue were not affected by photoperiod. The most important characteristics of the photoperiodic regulation of energy balance in the field vole are the clear delineation between phases where animals regulate body mass at two different levels and the rate at which animals are able to switch between different levels of energy homeostasis. Our data indicate that the field vole may provide an attractive novel animal model for investigation of the regulation of body mass and energy homeostasis at both organism and molecular levels.

Response of broilers susceptible to ascites when grown in high and low oxygen environments

1. Broilers selected on the basis of food conversion efficiency or growth rate were grown under normal (21%) or varied (19%, 23%) oxygen environments. 2. Broilers selected for food conversion efficiency had greater growth rates and superior food conversion efficiencies than broilers selected for growth rate. No interactions between broiler strain and oxygen level were observed. 3. Increasing environmental oxygen level decreased N efficiency in both broiler strains. Nitrogen turnover was non-significantly decreased. 4. Ascites may only occur when broilers are able to cope with small environmental adversities while maintaining optimal growth rates.

Energy and nitrogen metabolism and oxygen use by broilers susceptible to ascites and grown at three environmental temperatures

1. An experiment using respiration calorimetry was performed to examine the energy and nitrogen metabolism of 2 strains of male broilers grown at 3 environmental temperatures; the results were then related to the susceptibility of the strains to the ascites syndrome. 2. Broilers selected for food conversion efficiency were less responsive to environmental temperature than were broilers selected principally for increased weight gain. 3. The susceptibility to ascites of broilers selected for food conversion efficiency may be the result not of a genetic incapacity to use oxygen but of the ability of the bird to maintain growth rate in adverse thermal environments.

Early-life food restriction of broiler chickens. I. Methods of application, amino acid supplementation and the age at which restrictions should commence

1. Three experiments were performed to examine practical methods of early-life food restrictions and to examine the influence of increased dietary lysine or methionine on bodyweight recovery during re-alimentation in broiler chickens. 2. Food intake of broiler chicks was restricted quantitatively or by dietary dilution at 3 ages and the birds slaughtered at 49 d of age. The success of each food restriction was measured in terms of bodyweight recovery and body fat content. 3. Discontinuous food restriction and restriction by dietary dilution produced similar effects to a previously established food restriction regime. Bodyweight recovery was complete and fat contents depressed. FCR was inconsistently affected. 4. Supplementation of the finisher diet with lysine and/or methionine produced no conclusive results when this diet was fed to broilers previously subjected to early-life food restriction.