Glucose-induced norepinephrine levels and obesity resistance.

The value of glucose-stimulated sympathetic activation in differentiating rats that would subsequently resist or develop diet-induced obesity (DIO) when chronically fed a high-calorie diet (CM) enriched in fat and sucrose was tested in 3-mo-old male Sprague-Dawley rats. While the rats were on chow the areas under the curve for plasma glucose, insulin, and norepinephrine (NE) levels were measured for 60 min after an intravenous glucose load (1 g/kg). Half of the rats then switched to the CM diet for 14 wk developed DIO with 54% more weight gain and 205% heavier retroperitoneal fat pads; half [diet resistant (DR)] had weight gain and pad weights comparable to chow-fed controls. Caloric intake was comparable in all animals. NE areas after intravenous glucose loads were 54% lower in DR than DIO rats, and there was a positive correlation (r = 0.63) between these NE areas and subsequent weight gain on the CM diet. Areas under the insulin curve correlated with subsequent weight gain on chow (r = 0.71) but not the CM diet. These results suggest that rats predisposed to become DR on the CM diet have dampened sympathetic activation after a glucose load, possibly because of heightened end-organ responsiveness to NE.