Endocrine Abstracts

Diet induced obesity is associated with an increased relative risk of developing type 2 diabetes, hypertension, dyslipidemia and cardiovascular complications. In addition to these co-morbidity factors there is increasing evidence to suggest that obese insulin resistant individuals show impaired negative feedback control of the HPA axis in response to stress. Here we investigate HPA axis response to an acute stress following high fat feeding in rats.

Male Wistar rats (150–175 g; n=8/group) were randomly assigned to receive either standard rat chow (SC; RM1) or a high fat diet (HF; 45% kcal lard) for 12 weeks. Animals were housed in cages of two and food and water were provided ad libitum. Weight was monitored weekly and blood samples taken every 3 weeks to monitor glucose and insulin. On the test day one animal from each cage was exposed to an elevated plus maze for 15 min and their cage-mate killed immediately. The proportion of entries and time spent in open and closed arms were recorded as a measure of anxiety. Animals were killed by cervical dislocation. Tissues and trunk blood collected for analysis.

HF animals gained significantly more weight and had higher circulating plasma glucose compared to controls. Adrenal mass was greater in HF animals whilst thymus weight was reduced. Basal plasma corticosterone levels were higher in non-stressed HF animals compared to their non-stressed SC counterparts. On exposure to the elevated plus maze plasma corticosterone was higher in both SC and HF groups compared with unstressed animals and higher than SC rats. HF animals made more total arm entries and spent more time in the open arms.

These findings suggest that high fat feeding raises basal corticosterone levels, which may be associated with increased activity and decreased anxiety related behaviour in the elevated plus maze.