Fig. 4.

Impaired changes in substrate oxidation in melanocortin receptor knockout mice are associated with increased fat balance. Obese female Mc4r^−/− mice exhibit a delayed reduction in the RER following the transition from a low- to high-fat diet (A). (B) The balance of nutrient intake and oxidation is calculated using the mean RER over 3d for mice fed the high fat diet; the balance of carbohydrate intake and oxidation is comparable between all Mc4r^−/− and wild type mice, with an imbalance limited to fat metabolism. In A and B, obese female leptin deficient (Lep^ob/Lep^ob) mice were included in the study as an obese control. (C) Lean male Mc3r^−/− mice exhibit a comparable imbalance of fat intake and oxidation when fed a high fat diet. In an experiment using lean male Mc3r^−/− and wild type littermates at 3 months of age, fat balance was significantly higher in Mc3r^−/− mice compared to wild type, whereas the balance of carbohydrate intake and oxidation was similar between strains. (A and B) reproduced with permission from [2]. Significantly different intake (B), or between groups indicated by bars (C), *P < 0.05.