Thermogenesis in the marsupial Sminthopsis crassicaudata:: effect of catecholamines and diet

The fat-tailed dunnart (Sminthopsis crassicaudata) is a small carnivorous marsupial with detectable brown adipose tissue. In order to determine whether catecholamines and food intake increase thermogenesis in this species, we measured the response of oxygen consumption ((V) over dot O-2) to (i) intraperitoneal noradrenaline (0.25-4.0 mg kg(-1)), and (ii) food intake. The effect of nutritional status and macronutrient composition of the diet on the (V) over dot O-2 response to food intake was determined by feeding both non-deprived and 24-h-food-deprived animals with either laboratory diet (1.01 Kcal g(-1) (4.2 KJ g(-1)), 20% fat) or live mealworms (Tenebrio molitor larvae) (2.99 Kcal g(-1) (12.5 KJ g(-1)), 30% fat). Intraperitoneal injection of noradrenaline at doses of 0.25 and 0.5 mg kg(-1) increased (V) over dot O-2 by 14% and 31% respectively at 30 min (P less than or equal to 0.05), whereas noradrenaline at 2 and 4 mg kg(-1) decreased (V) over dot O-2 by 10% and 31% respectively (P less than or equal to 0.05). Following food intake, (V) over dot O-2 increased in both non-deprived (P i 0.05) and 24-h-food-deprived (P < 0.05) animals. While the magnitude of the increase in (V) over dot O-2 was similar in animals fed with either laboratory diet or mealworms, both diets increased (V) over dot O-2 more in non-deprived than in 24-h-food-deprived animals (P < 0.05). These results suggest that in S. crassicaudata (i) catecholamines increase thermogenesis and (ii) the magnitude of diet-induced thermogenesis is dependent on both the nutritional status of the animal and the macronutrient composition of the diet.