Intracarotid glucose induced norepinephrine response and the development of diet induced obesity

Intracarotid glucose infusions cause increased plasma norepinephrine (NE) levels in some rats. This is used as an index of sympathetic activation. Similar increases in plasma NE levels are produced by intravenous glucose injections and these levels correlate positively with the amount of weight gained by adult rats when they are subsequently fed a diet enriched in calories, sucrose and fat (condensed milk (CM) diet) for three months. Thus, rats prone to develop diet induced obesity (DIO) on the CM diet have greater intravenous glucose induced NE responses than those which are diet resistant (DR). To test the hypothesis that this relationship is mediated by the brain, 17 chow fed, adult male Sprague-Dawley rats were infused for 60 min with intracarotid glucose at 4 mg/kg/min and blood samples were obtained for plasma catecholamines, insulin and glucose. They were then placed on the CM diet for three months. After three months on the CM diet, there was a wide variability in body weight gain and the weights of retroperitoneal fat pads, an indirect measure of carcass adiposity. For all 17 rats, there was a significant correlation between both body weight gain (r = 0.685, P = 0.002) and retroperitoneal fat pad weights (r = 0.590, P = 0.013) with the levels of plasma NE reached 45-60 min into the preceding intracarotid glucose infusions. For the six lowest and six highest glucose induced NE responders, the correlation between NE response and body weight gain on CM diet was r = 0.944 (P = 0.0001). Plasma epinephrine, insulin and glucose levels were unchanged during such infusions.(ABSTRACT TRUNCATED AT 250 WORDS)