Abstract 3671: Dietary-induced Obesity in Mice results in Metabolic and Vascular Insulin-like Growth Factor 1 Resistance
Endothelial cell dysfunction, characterised by a reduction in the bioavailability of nitric oxide (NO), plays an important role in the initiation of atherosclerosis. IGF-1 may be involved in the regulation of NO production via the Phosphoinositide 3-kinase (PI3-K)/Akt/eNOS pathway. In this study we have investigated whether dietary-induced obesity leads to disturbances of this pathway. C57/Blk6 mice fed a high fat diet for 20weeks (n=12) showed a significant increase in body weight and fat pad size when compared to chow fed controls (n=12). Blood pressure measurement showed an age-related increase in systolic blood pressure in high fat fed (19.2% from baseline) versus chow fed mice (7.6% from baseline). Blood glucose levels increased from 13.5 to 20mmol/l at 120mins in high fat fed mice, versus 5.7 to 7.3mmol/l in the chow fed group (p=0.009) by tolerance testing. In response to insulin, blood glucose fell by 72% in the chow fed group versus 48% in the high fat fed group (p= 0.0002). The high fat fed mice were less sensitive to IGF-1 stimulation than the chow fat mice by IGF-1 tolerance testing (p=0.046 at 30mins). The basal protein level of phosphorylated eNOS in the aortae of the high fat fed mice was 24.2% less than that of the chow fed mice. Upon IGF-1 stimulation levels of phosphorylated eNOS increased by 45.1% in the chow fed mice compared to a slight decrease of 5% in the high fat fed mice after normalisation to eNOS protein levels. eNOS activity in the aortae of chow fed mice, measured by an ex-vivo L-citrulline assay, showed an increase of 1.6-fold in response to IGF-1 (100 nM; 10 minutes) when compared to the high fat fed mice (n=5; p<0.01). Pre-incubation of aortae with the NOS inhibitor, L-NAME (1 mmol/L; 30 minutes) prior to stimulation with IGF-1 completely inhibited eNOS enzyme activity (n=5; p<0.05). Ex-vivo constriction curves from aortic rings showed phenylephrine induced constriction was blunted by IGF-1 causing vasorelaxation in chow fed mice. This relaxation effect was blocked in high fat fed mice. These data suggest that dietary-induced obesity results in resistance to IGF-1 at both a metabolic and vascular level via an endothelial/PI3-K/NO dependent mechanism.