Figure 2. Reduced thermogenesis and heart rate (HR) in Pet-1^−/− (KO) neonates during ambient cooling.

A, raw traces showing the changes in the fractional concentration of O₂ leaving the mask (mask O₂) and body temperature (T_B) in Pet-1^−/− animals (n = 5, grey lines) and littermates (WT) (n = 5, black lines) as ambient temperature (T_A) is cooled from 34°C to 29°C over 25 min (shaded region). B, at 34°C, metabolic rate is not significantly different in Pet-1^−/− animals compared to WT. The disparity between genotypes becomes apparent as T_A is reduced to 29°C (shaded region). C, at 34°C, T_B is slightly but significantly lower in Pet-1^−/− animals compared to WT. As is the case with , the disparity becomes greater with cooling to 29°C. D, there were no differences in tail temperature (T_T) between Pet-1^−/− and WT animals at either T_A. Note: T_T is less than 29°C because of a T_A gradient within the chamber (T_A was 1.5°C lower at the tail end compared to the middle). E, there is a significantly greater reduction in HR with cooling in Pet-1^−/− animals compared to WT. All data in B–E are means ± SE. *Significant genotype effect, P < 0.05; †genotype ×T_A interaction, P < 0.05.