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Effects of Diet on Norepinephrine Turnover in Obese (ob/ob) Mice¹

School of Human Development, The University of Oklahoma, Norman, OK 73019 ^* Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48824-1224

Effects of energy restriction and of supplemental sucrose or fat on norepinephrine (NE) turnover in brown adipose tissue (BAT) and heart of female obese (ob/ob) and lean mice were examined. Rates of NE turnover in BAT of control female obese mice (8 weeks old) were 39% lower than in control lean mice; no differences were evident in hearts of these mice. Energy intake of 6-week-old ob/ob mice was restricted to the intake of lean mice for 2 weeks. This restriction decreased intake by 41% and reduced rates of NE turnover in heart (-15%), but not in BAT, of obese mice. Next, 7-week-old lean and obese mice were given access to stock diet and a 30% sucrose solution for 3–4 days. Intake of stock diet decreased by more than 50%. Total energy intake increased in lean mice (+18%), but decreased (-19%) in obese mice. When a 10% sucrose solution was offered intake of stock diet still decreased, but total energy intake was unchanged in lean and obese mice. Oxygen consumption increased in lean mice (+19 to +24%), but not in obese mice, when fed either 30 or 10% sucrose solutions, or a fat-supplemented diet where fat isocalorically replaced the sucrose consumed from 30% sucrose solution. Rates of NE turnover were not significantly increased in lean mice fed the 30% sucrose solution, but were increased in BAT (+34%) and heart (+25%) in lean mice fed the fat-supplemented diet. In obese mice rates of NE turnover were increased in BAT (+40%) and heart (+33 to +47%) when fed either the 30% sucrose solution or the fat-supplemented diet. Thus, obese mice failed to exhibit dietary-induced thermogenesis even though the dietary manipulation increased rates of NE turnover in their BAT. Possibly BAT of obese mice is refractory to NE in short-term feeding trials.

KEY WORDS: • norepinephrine turnover • brown adipose tissue • heart • oxygen consumption • diet • obese (ob/ob) mice

¹ Supported by the National Institute of Arthritis, Diabetes, Digestive and Kidney Diseases of the National Institutes of Health, grant no. AM 15847. Michigan State University Agricultural Experiment Station journal article no. 11192.

Manuscript received 26 March 1984.