TABLE 1.
Lipid content and lipid loss of BAT during 16.5 min NA-induced thermogenesis
| Acclimation Temperature | Genotype | n | Lipid Content of iBAT before NA (mg)a | Lipid Content of iBAT 16.5 min after NA (mg)a | Lipid Loss of iBAT (mg/16.5 min) | Estimated Lipid Loss of Total BAT (mg/16.5 min)b |
| 30°C | WT | 8 | 97.19 ± 13.0 | 82.04 ± 11.8 | 11.37 ± 2.5 | 28.42 ± 6.3 |
| UCP1-KO | 8 | 93.41 ± 9.6 | 88.92 ± 8.7 | 8.28 ± 2.3 | 20.69 ± 5.8 | |
| 18°C | WT | 7 | 37.18 ± 8.3 | 25.46 ± 6.0 | 11.72 ± 3.1 | 29.29 ± 7.8 |
| UCP1-KO | 10 | 38.02 ± 3.8 | 32.28 ± 2.4 | 5.74 ± 1.9 | 14.35 ± 4.7 | |
| 5°C | WT | 8 | 32.89 ± 4.6 | 23.63 ± 3.4 | 9.26 ± 1.6 | 23.15 ± 4.1 |
| UCP1-KO | 10 | 31.37 ± 2.8 | 26.02 ± 2.2 | 5.35 ± 1.8* | 13.38 ± 4.37* |
Calculations are based on proton spectroscopy of the iBAT depot. UCP1-KO and WT mice were sequentially acclimated to ambient temperatures of 30°C, 18°C, and 5°C. Values are means ± SEM. Statistically significant differences between the genotypes at each acclimation temperature (P ≤ 0.05) are indicated with *.
Calculation of lipid content from proton spectroscopy: lipid (mg) = I × V × A/B. I, integral of (CH2)n peak from lipid spectrum; V, iBAT volume regarding MRI; A = 0.000286, conversion factor calculated from oil phantoms with lipid spectroscopy; B = 0.0031 ml, volume of interest in single voxel proton-spectroscopy.
Lipid consumption of total BAT = (lipid content of iBAT before NA − lipid content of iBAT after NA) × 100/40. We estimated that the iBAT accounts for 40% of total BAT. According to Heldmaier (7) iBAT of albino mice makes up 50% of total BAT (without the perirenal depot). According to Thurlby and Trayhurn (21) iBAT of “Aston” mice makes up 34% of total BAT (without periaortic sites). According to own observations iBAT of C57/Bl6 mice represents 52% of total BAT (without perirenal and subventral depots).