Effect of diet on the response to leptin in the marsupial Sminthopsis crassicaudata.
The aim of this study was to determine in the marsupial Sminthopsis crassicaudata 1) the effect of leptin on food intake, body fat stores, and metabolism and 2) whether leptin can prevent a diet-induced increase in adiposity. In response to 21 days of feeding with mealworms (2.99 kcal/g, 30% fat), body weight (P < 0. 0001) and tail width (P < 0.0001) increased, compared with control animals fed with laboratory diet (1.01 kcal/g, 20% fat). Subsequently, S. crassicaudata were randomly allocated to receive either laboratory diet or a choice between laboratory diet and mealworms. For 13 days, one-half of the animals in each dietary group received intraperitoneal human leptin (2.5 mg/kg twice daily), while the other one-half received phosphate-buffered saline. In animals receiving laboratory diet alone, leptin induced a decrease in body weight (P < 0.0001), tail width (P < 0.0001), and energy intake (P < 0.01). In animals receiving both laboratory diet and mealworms, leptin had no effect on body weight or tail width, although the proportion of laboratory diet eaten was reduced (P = 0. 0001), and there was a nonsignificant fall in overall energy intake (P = 0.07). We conclude that in S. crassicaudata, 1) a high-calorie, higher-fat diet induces an increase in adiposity and 2) leptin induces weight loss, but 3) an increase in dietary calories and fat content is associated with resistance to the actions of leptin.