Effect of dietary macronutrients on food intake, body weight, and tail width in the marsupial S. crassicaudata

Effect of dexamethasone on hypothalamic expression of appetite-related genes in chickens under different diet and feeding conditions

BACKGROUND

Glucocorticoids (GCs) are involved in the control of appetite in birds and mammals. The effect of GCs on feed intake in birds depends on their dietary energy level. But the regulation mechanism of GCs on appetite is still unclear in chickens facing to different energy level. An experiment was conducted to investigate the effect of dexamethasone (DEX) on hypothalamic expression of appetite-related peptides in chickens fed high/low fat diet and under fasting/feeding condition.

RESULTS

An interaction between DEX injection and dietary energy level was found on hypothalamic corticotropin-releasing hormone (CRH) gene expression in fasted chickens (P < 0.05). The chickens, given a DEX injection and a low fat diet treatment, had the highest CRH mRNA levels than any of the fasted chickens given treatments (P < 0.05). Under fasting conditions, the DEX treatment significantly increased hypothalamic neuropeptide Y (NPY) and GC receptors mRNA levels (P < 0.05). Under re-feeding conditions, DEX treatment significantly decreased hypothalamic expression levels of NPY and agouti-related peptide (AgRP) but significantly increased the level of hypothalamic CRH expression (P < 0.05).

CONCLUSION

A regulatory network formed by NPY, AgRP and CRH is associated with the appetite-control by GCs. The result suggests that the regulation of GCs on orexigenic neuropeptides expression is dependent at least partially on dietary energy level and feeding state.

Mice with Low Metabolic Rates Are Not Susceptible to Weight Gain When Fed a High-Fat Diet

OBJECTIVE

Mice divergently selected for high or low food intake (FI) at constant body mass differ in their resting metabolic rates (RMRs). Low-intake individuals (ML) have significantly lower RMR (by 30%) compared with those from the high-intake line (MH). We hypothesized that MLs might, therefore, be more likely to increase their body and fat mass when exposed to a high-fat diet (HFD).

RESEARCH METHODS AND PROCEDURES

We exposed both lines to a diet with 44.9% calories from fat for 3 weeks while measuring FI, fecal production, and body mass and then returned the mice to standard chow.

RESULTS

When exposed to the HFD, both lines significantly decreased their FI (MH, 40% to 45%; ML, 31% to 35%). This decrease occurred simultaneously with a significant increase in apparent energy absorption efficiency (AEAE). When returned to chow, FI and AEAE returned to the levels observed prior to HFD exposure. Because of the adjustments in FI, the absorbed energy was maintained in the MLs and, thus, body mass remained constant. The MH individuals overcompensated for the elevated energy content and AEAE on the HFD and, therefore, absorbed lower energy than when feeding on chow. These mice also did not significantly change their body mass when on the HFD and must have made adjustments in their energy expenditures. Both lines and both sexes increased in fat content on the HFD, but these effects were not different between lines or sexes.

DISCUSSION

We found no support for the hypothesis that mice with low RMRs were more susceptible to weight gain when fed the HFD.

Rate of passage through the digestive tract of the kultarr (Antechinomys laniger)

The kultarr (Antechinomys laniger) is a small insectivorous marsupial that has undergone significant declines in geographical range. Limited studies have been undertaken on kultarr biology and therefore there is a lack of understanding of its basic biological and ecological requirements. Rate of passage in the kultarr, determined using mealworm cuticle as a marker in minced beef, was 1.6 ± 0.2 h and mean retention time was 3.9 ± 1.2 h. The rapid transit time was consistent for an animal of equivalent body mass, dietary preference and gastrointestinal tract morphology. Mean retention time was short, similar to that of other mammals with a small body mass. This study provides the first insight into gastrointestinal physiology of the little known kultarr.

Carbohydrate-to-fat ratio affects food intake and body weight in Wistar rats

The aim of the study was to evaluate the impact of carbohydrate-to-fat ratio on body weight and appetite regulation in Wistar rats. Twenty-four Wistar rats were randomized to three dietary groups (n = 8): normal carbohydrate diet (NC), low-carbohydrate diet (LC) and high-carbohydrate diet (HC) for 12 weeks. Body weight and food intake were recorded. Circulating leptin and insulin levels were measured by radioimmunoassay method. The expression levels of leptin receptor, insulin receptor, orexin, neuropeptide Y (NPY), agouti-related protein (AgRP) and melanocortin-4 receptor (MC-4R) in the hypothalamus were also measured by realtime polymerase chain reaction (PCR). In the LC group, food intake reduced while body weight increased significantly compared with the NC and HC groups. Plasma leptin levels increased in the LC (18.5 +/- 8.2 ng/mL) group compared with the NC (8.6 +/- 3.8 ng/mL, P < 0.001) and HC (6.6 +/- 1.9 ng/mL, P < 0.001) groups. Realtime reverse transcription-PCR revealed a decrease in the hypothalamic expression level of only leptin receptor in the LC (0.764, 0.471-4.648 copy/mL) and HC (0.357, 0.129-0.781 copy/mL) groups compared with the NC (1.323, 0.616-2.392 copy/mL; P = 0.01) group, and that there was no significant change in those of insulin receptor, AgRP, Orexin, NPY and MC-4R. Low-carbohydrate, high-fat diet raised body weight, which led to a rising of circulating leptin levels and a reduced expression of leptin receptor in the hypothalamus.

The effects of high fat on central appetite genes in Wistar rats: a microarray analysis

BACKGROUND

To evaluate the effects of high fat on central appetite regulatory genes in Wistar rats by microarray.

METHODS

Sixteen male Wistar rats were randomly assigned to control (15% energy from fat) and high-fat (60% energy from fat) diets for 12 weeks. Body weight and food intake were recorded. Plasma leptin, ghrelin and insulin were measured by radioimmunoassay method. The expression of 111 appetite regulatory genes in the hypothalamus was evaluated by microarray and six genes, including leptin receptor, insulin receptor, orexin, NPY, AgRP, MC-4R, were further evaluated by real-time RT-PCR.

RESULTS

Body weight increased significantly in HF group compared with control group, whereas energy intake was similar in the two groups. HF had a time dependent effect on plasma leptin, but insulin and ghrelin level remained stable throughout the study. A positive relation was also found between body weight and plasma leptin (r=0.88, P<0.01). The expression of 27 appetite genes in the hypothalamus was significantly affected by HF diet. However, only the expression of leptin receptor was confirmed lower in HF group than that in control by real-time PCR, which suggested that lower expression of leptin receptor might be another reason for leptin resistance.

CONCLUSIONS

HF diet fed rats demonstrated leptin resistance, which could be targeted for obesity treatment.

Effect of high-fat diet on body mass and energy balance in the bank vole

We tested the hypothesis that animals that reduce their body mass in response to decreased photoperiod do not develop diet-induced obesity (DIO) when fed a high-fat diet (HFD). Bank voles (Clethrionomys glareolus) fed a diet with fat content of 13.5% by mass and 28.2% by energy, for 5 weeks, did not develop hyperphagia and were resistant to DIO, consistent with predictions. There was no significant difference between food (g/day) or energy intake (kJ/day) between the experimental or control group (fed a standard diet with fat content of 5.4% by mass and 12.3% by energy) over the duration of the experiment. However, as a result of a higher apparent energy assimilation efficiency (AEAE), voles fed the HFD assimilated significantly more energy over the 5-week period. Furthermore, they consumed twice as much fat per day as controls. There were no significant differences in resting metabolic rate (RMR) over time or between groups over the 5-week period. In conclusion, bank voles achieved resistance to DIO despite assimilating more energy than control animals fed the standard diet and taking in twice as much fat. Resistance did not occur by modification of RMR, implicating differences in activity levels.