The Effect of Kappa Opioid Receptor Antagonism on Energy Expenditure in the Obese Zucker Rat

Food intake and, subsequently, body weight are influenced by endogenous opioids acting in the central nervous system. Agonists for the opioid receptor increase food intake, whereas antagonists reduce food intake. Body weight, however, is the result of food consumed and energy expended. Although much has been reported about the effect of opioid antagonism on food intake, less has been reported about its effect on energy expended. This study investigated the effect of selective antagonism of the kappa opioid receptor on food intake, body weight, and indicators of energy expenditure in male obese Zucker rats (n= 10). Energy expenditure was measured by indirect calorimetry, whereas general activity and body temperature were measured by implanted radio frequency telemetry. Central administration of 30 µg of the kappa opioid receptor (KOR) antagonist norbinaltorphamine resulted in a significant 34% reduction in food intake (p = .001), a small reduction in body weight, a reduction in resting energy expenditure (p = .06), a reduction in respiratory quotient (p = .06), a 14% reduction in general activity, and a reduction in core body temperature. Reduction in body weight as a result of KOR inhibition in this study was related to a decrease in food intake but not related to an increase in energy expended or activity.

Obesity in urban women: associations with sleep and sleepiness, fatigue and activity

BACKGROUND

African-American women (AAW) have the highest prevalence of obesity and therefore are at greater risk for obesity-related symptoms and diseases. Obese individuals frequently report poorer sleep quality, more daytime sleepiness, more severe fatigue, and higher physical inactivity than normal weight individuals. The relationships among these variables have not been well-characterized in obese, urban-dwelling, AAW.

METHODS

This descriptive, correlational study examined the relationships among sleep quality, daytime sleepiness, fatigue, level of physical activity, and body mass index (BMI) in AAW living in an urban setting. A convenience sample of 69 young adult women with a BMI of greater than 30 kg/m(2) completed measures of sleep quality, sleepiness, fatigue severity, sense of community, and physical activity. Further analysis was done to determine if any of the study variables predicted level of physical activity.

FINDINGS

There was a strong and significant correlation between BMI and overall fatigue severity and a significant, negative correlation between BMI and physical activity performance. BMI was significantly correlated with sleep latency but not global sleep quality. There were significant relationships between fatigue severity and poorer global sleep quality and daytime sleepiness. Multiple regression analysis showed BMI and age accounted for a significant amount of the variance in physical activity.

CONCLUSIONS

Higher BMI was associated with significant fatigue. Fatigue severity was associated with poorer global sleep quality, daytime sleepiness, and a sense of community. Higher BMI may be a barrier to having an active lifestyle.

Effects of gender on locomotor sensitivity to amphetamine, body weight, and fat mass in regulator of G protein signaling 9 (RGS9) knockout mice

Regulator of G-protein signaling (RGS) protein 9-2 is enriched in the striatum where it modulates dopamine and opioid receptor-mediated signaling. RGS9 knockout (KO) mice show increased psychostimulant-induced behavioral sensitization, as well as exhibit higher body weights and greater fat accumulation compared to wild-type (WT) littermates. In the present study, we found gender influences on each of these phenotypic characteristics. Female RGS9 KO mice exhibited greater locomotor sensitization to amphetamine (1.0mg/kg) treatment as compared to male RGS9 KO mice. Male RGS9 KO mice showed increased body weights as compared to male WT littermates, while no such differences were detected in female mice. Quantitative magnetic resonance showed that male RGS9 KO mice accumulated greater fat mass vs. WT littermates at 5months of age. Such observations could not be explained by increased caloric consumption since male and female RGS9 KO mice demonstrated equivalent daily food intake as compared to their respective WT littermates. Although indirect calorimetry methods found decreased oxygen consumption and carbon dioxide production during the 12-hour dark phase in male RGS9 KO vs. WT mice which are indicative of less energy expenditure, male RGS9 KO mice exhibited lower levels of locomotor activity during this period. Genotype had no effect on metabolic activities when KO and WT groups were compared under fasting vs. feeding treatments. In summary, these results highlight the importance of factoring gender into the experimental design since many studies conducted in RGS9 KO mice utilize locomotor activity as a measured outcome.

Toward a Middle-Range Theory of Weight Management

The authors of this paper present the middle-range theory of weight management that focuses on cultural, environmental, and psychosocial factors that influence behaviors needed for weight control. The theory of weight management was developed deductively from Orem's theory of self-care, a constituent theory within the broader self-care deficit nursing theory and from research literature. Linkages between the conceptual and middle-range theory concepts are illustrated using a substruction model. The development of the theory of weight management serves to build nursing science by integrating extant nursing theory and empirical knowledge. This theory may help predict weight management in populations at risk for obesity-related disorders.

The effect of α-cyclodextrin on postprandial lipid and glycemic responses to a fat-containing meal

OBJECTIVE

α-Cyclodextrin (α-CD), a soluble dietary fiber derived from corn, marketed under the trade name FBCx®, has the potential to help individuals manage their weight and improve their lipid profiles. Initial studies in healthy overweight and/or obese diabetic individuals found that, in those consuming a normal to high fat diet over a 4 or 12 week period, α-CD use was associated with weight loss or maintenance and a reduction in triglyceride (TG) and cholesterol levels in hyperlipidemic individuals. Furthermore, α-CD use was associated with the positive effects of increasing insulin and leptin sensitivities. To date, the immediate post-prandial glucose and lipid responses to a fat-containing meal have not been reported.

MATERIALS/METHOD

This double blinded placebo controlled cross-over trial examined the effect of 2 g of α-CD taken immediately following consumption of a commercially prepared high-fat breakfast meal on the acute postprandial responses in healthy adults.

RESULTS

The coincidental consumption of α-CD with a fat-containing meal was associated with a significant reduction in postprandial TG responses over time when compared to placebo. When incremental area under the curve was calculated, the area under the curve associated with α-CD consumption was significantly smaller than the Placebo area (0.30±1.07 mmol/L/3 h vs. 0.98±0.88 mmol/L/3 h, p<0.05). There were no significant changes in glucose or cholesterol levels.

CONCLUSION

α-Cyclodextrin was shown to significantly lower acute postprandial blood triglyceride levels.

Implications of the biology of weight regulation and obesity on the treatment of obesity

PURPOSE

The purposes of this article are to provide a brief review of the complex biology of weight regulation and obesity, to explain some of the effects of diet and exercise on the biology of weight regulation and obesity, and to propose a coherent way to assess and treat people related to weight and obesity.

DATA SOURCES

Scientific publications, clinical guidelines, and government sources.

CONCLUSIONS

Obesity is a complex problem requiring an understanding of how interventions interact with the biology of weight regulation in people who are obese. Promoting health in obese people requires a focus on improving insulin sensitivity.

IMPLICATIONS FOR PRACTICE

Helping individuals maintain normal weight throughout life is important in order to keep the long- and short-term weight signals in balance and reflective of true energy requirements. Exercise is associated with loss of total and abdominal adipose tissue and improved insulin sensitivity. Diets inducing gradual weight loss are less likely to stimulate appetite. Diets should include antioxidants to neutralize the increase in free radical production associated with obesity and exercise. Other interventions in the treatment of obesity may include treating sleep deficits and the dysregulated endocannabinoid system.

Effects of abuse pattern of gestational toluene exposure on metabolism, feeding and body composition

AIMS

Inhalant abuse during pregnancy lowers birth weight and impedes early development. These studies explored the effects of brief, repeated, prenatal toluene exposures in pregnant female rats on body weight, metabolic rate, body composition, and food intake in their offspring.

METHOD

Rats were exposed to 0, 8000, 12,000, or 16,000 ppm of toluene twice daily for 15 min from gestational days 8 to 20. The effects of such exposures on post-weaning litter weights, oxygen consumption, carbon dioxide output, and body fat content were determined in 2 cohorts (n=23, n=24) of offspring. Food intakes and weight changes in response to 3 different diets (regular chow, purified diet, purified high fat diet) were examined in another cohort (n=24) from postnatal days 72 to 116.

RESULTS

Litter weights showed a significant linear decrease as a function of toluene dose. Offspring exposed to the 16,000 ppm toluene dose displayed statistically lower energy expenditures than control rats. Male rats exposed to 8000 or 16,000 ppm toluene had significantly greater percentage of body fat as well as total body fat than the other groups. Toluene also significantly suppressed weight gain over the time chow was consumed compared to the 0 ppm control group. Finally there were trends for a main effect of toluene dose on food intake during chow and during high fat diet consumption, with rats in the 12,000 ppm group consuming more than the 0 ppm group on both diets.

DISCUSSION

These data suggest that, in addition to other previously documented abnormalities in neurological development and behavior, the physiological regulation of metabolism and body composition in males as well as food intake and weight gain in both sexes may be altered by prenatal exposure to toluene.

Disordered eating and food cravings among urban obese African American women

OBJECTIVE

The prevalence of night eating syndrome (NES), binge eating disorder (BED), and bulimia nervosa (BN) and the general experience of food cravings were examined in 88 obese urban African American women.

METHOD

Participants were administered The Questionnaire on Eating and Weight Patterns-R, the Night Eating Syndrome Questionnaire, and the State and Trait Food Cravings Questionnaire, Trait version (FCQ-T).

RESULTS

Twenty-eight percent reported symptoms of eating disorders (18.9% NES, 6.4% recurrent binge eating, 2.2% both NES and recurrent binge eating). Those reporting disordered eating had significantly higher total FCQ-T scores than those not reporting disordered eating. Persons endorsing recurrent binge eating had the highest mean score, followed by those reporting NES. Those who identified themselves as binge eaters and night eaters were not significantly different from each other, but both groups were significantly different than the no eating disorder symptoms group on various subscales of the FCQ-T.

DISCUSSION

Obese African American women report significant levels of NES and binge eating which may contribute to the development and/ or maintenance of obesity.

Conditioned place preferences (CPPs) to high-caloric "snack foods" in rat strains genetically prone vs. resistant to diet-induced obesity: resistance to naltrexone blockade

A previous study in our laboratory using Sprague-Dawley (SD) male rats showed that conditioned place preferences (CPPs) can be learned to two different high-caloric "snack foods"--one high in sugar (Froot Loops cereal: FL) vs. one high in fat (Cheetos: C), and that both preferences were mediated by endogenous opioids. Using the same CPP apparatus and procedures, two genetic sub-strains of SD rats, one selectively bred for diet-induced obesity (DIO) vs. another bred for diet resistance to obesity (DR), were used in this investigation. The experiment determined if (a) CPPs can be created in both strains using the same high-caloric "snack foods" and, (b) if CPPs existed, were they opioid dependent. Four non-deprived groups of eight male rats, half being of each strain, were given 20 min sessions to eat either FL or C in one side of a three-chamber CPP apparatus vs. chow on the opposite side over alternating days of a 20 day period. Each predetermined side had distinctly different environmental cues. Following conditioning, rats were tested during 10 min sessions to see if CPPs existed to the "snack food" trained sides. During conditioning and testing, bodyweights, intakes of foods, and activity were measured. Both FL and C generated strong CPPs that were equivalent in both strains. In contrast to our previous study in the parent strain, doses of 0, 0.50, 1.0, 2.5, and 5.0 mg/kg of the opioid antagonist, naltrexone, had no effect on blocking these CPPs. These results show that (a) DIO and DR rats can learn CPPs (i.e., "exhibit food cravings") as well as their parent strain after periodic access to high-caloric palatable foods, but imply that (b) some physiological system other than the endogenous opioid system mediates such learning.

Effect of opioid antagonism on conditioned place preferences to snack foods

Previous research has shown that food-deprived rats acquire conditioned place preferences (CPPs) to sweet liquids that are largely attenuated by the opioid antagonist naltrexone (NAL). This study determined if ad libitum Chow-fed rats can learn CPPs when given relatively brief exposures to different solid snack foods (SFs) -- one high in sugar (Froot Loops cereal: FL) vs. one high in fat (Cheetos: C). Two groups of 16 male rats were trained during 20-min sessions to eat either FL or C in one side of a three-chambered CPP apparatus vs. Chow in the opposite side on alternating days for 20 days. Rats ate considerably more SFs of both types than Chow during the conditioning sessions (SFs: about 23 kcal versus Chow: about 7 kcal). Ten-minute tests for CPPs in the absence of SFs showed that the time spent on SF-conditioned sides increased significantly compared to pre-conditioning tests. Analyses of variance for re-tested CCPs after 0.1, 1.0, 2.5, and 5.0mg/kg NAL showed dose-dependent suppressions of CPPs to both SFs. These data show that consuming sweet or fatty SFs can become reliably associated with environmental cues in the non-deprived state. The endogenous opioid system, which mediates hedonic aspects of palatable food intake, appears to mediate these learned associations.

The effect of opioid antagonism on food intake behavior and body weight in a biobehavioral model of obese binge eating

The obese Zucker rat (OZR) exhibits a hyperphagic eating pattern similar to the obese binge eater. Dynorphin, an endogenous agonist of the kappa receptor, is associated with regulation offood intake. Lessened sensitivity to opioid antagonists and/or increased central dynorphin levels may contribute to the hyperphagic eating pattern observed in the OZR. This study examined the temporal effect of a single intracerebroventricular (ICV) dose of nor-binaltorphimine (NBNI), a specific and long-lasting kappa opioid antagonist, on food intake, body weight, and satiety measures (meal size and the shape of the cumulative food intake curve [CFIC]) in adult male OZRs. Analysis of individual subjects revealed a differential response to opioid antagonism with respect to weight loss, reduction in food intake, and change in the slope of the CFIC, with some responding and others responding poorly. Repeated-measures analysis of variance showed a significant decrease in body weight (P = 0.001) and food intake (P = 0.03) in responders compared to poor responders and controls. Satiation was influenced to a greater extent in responders, who showed a significant reduction in meal size and a greater change in the CFICfor the largest meal of the day toward a pattern of satiation. These data suggest that a differential response to chronic opioid antagonism may exist in the OZR.

Effect of genetic obesity on thermoregulatory activity responses to inversion of the light/dark cycle

In this pilot work, the authors compared the circadian rhythm responses of 3-month-old female fatty Zucker rats with those of lean Zucker rats and Sprague-Dawley rats to reversal of the light/dark (LD) cycle. Core temperature and spontaneous cage activity were continuously monitored by implanted microtelemetry devices prior to and for 5 days following complete LD cycle reversal. By the 5th day after LD reversal, temperature rhythm nadir had phase-advanced 10.5 hours in the lean Zucker rats, 10.8 hours in the Sprague-Dawley rats, and only 3.8 hours in the fatty Zucker rats. Similarly, total activity increased in lean Zucker rats and Sprague-Dawley rats after LD reversal but declined in the fatty Zucker rat during the same time. Results of this study show that obese Zucker rats displayed an impaired ability to reentrain circadian rhythms for temperature and activity when compared to lean Zucker rats and Sprague-Dawley rats. These findings suggest that dysfunction in the circadian pacemaker previously shown to manifest itself by 43 weeks of age in fatty Zucker rats may already be present at 3 months of age and suggest that altered thermoregulation may play a role in the development of obesity in this animal model of genetic obesity.

The effect of a high-fat diet and exercise on the expression of genetic obesity

In the United States, there are 300,000 obesity-related premature deaths each year. Furthermore, no current obesity treatment program results in consistent weight reductions. Obesity is thought to be caused by complex genetic-environmental interactions. We studied the effect of two environmental factors, high-fat diet and non-weight-bearing exercise, on obesity expression. Young adult, female, genetically obese (fa/fa) rats (n = 52) and their lean (Fa/fa) littermates (n = 24) were studied using an experimental 2 x 2 x 2 factorial design (diet type, genetics, and exercise). Repeated measures ANOVA and secondarily stepwise regressions were used to analyze the data. The authors discovered that the effect of appetite on obesity expression is more limited than expected, and there may be critical stages when obesity expression is amenable to environmental modification.