Endocrine Abstracts

The consumption of a high energy (HE) diet causes a range of weight gain responses in the human population with some individuals resistant to diet induced obesity (DIO). The SD rat provides a model for DIO and this study examines the effects of HE diet on bodyweight, food intake and hypothalamic neuropeptide gene expression. 28 male out-bred SD rats (280.7±2.19g) were fed chow ad-libitum (AL) for 4 days then divided into 2 weight-matched groups: 20 rats were fed HE diet AL for 15wks then chow for 5wks, remaining 8 rats were fed chow (C) AL for 20wks. Rats exhibited a range of weight gains (HE: 224-401g; C: 187-361g). The top and bottom 40% of weight gainers on HE were designated as susceptible (DIO-S) and resistant (DR) to DIO, respectively. Caloric intake in wks 1-2 was higher in HE than C (105.6±2.96v90.4±1.6; P<0.05), but similar in wks 14-15. However on transfer of HE rats back to chow, intake decreased and was lower than C rats (71.8±0.77v87.0±1.04; P<0.05), yet HE rats maintained their bodyweight. Plasma leptin concentrations were similar in all groups. Hypothalamic sections were subjected to in situ hybridisation to assess NPY, AgRp, POMC, CART, ObRb, Mc3R and Mc4R gene expression using 35S-labelled riboprobes. AgRp mRNA in the arcuate nucleus was 50% higher in DIO-S than DR and C (P=0.053) and Mc4R mRNA in the paraventricular nuclues was 30% lower in DIO-S and DR than C (P<0.05). Gene expression was similar for all groups for all other neuropeptides/receptors measured. The results indicate HE rats will defend their bodyweight on transfer to chow through reduced energy expenditure and in DIO-S rats this could be mediated by the melanocortin system.