[Thermogenesis induced by diet in the 2- and 7-day-old Zucker rat]

Gas exchanges were measured at the thermoneutral temperature of 35 degrees C on "fasted" (3 h 30 min) and then "refed" (75 min) fa/fa and Fa/fa rats aged 2 and 7 days. The CO2 production, O2 consumption and respiratory quotient increased significantly after refeeding in all pups. The percentage of increase in the gas exchanges was similar in both genotypes at 2 days. At 7 days, the percentage of increase was significantly higher in Fa/fa than in fa/fa pups. This demonstrated a defect in diet-induced thermogenesis in 7-day old pups. However, since this defect (unlike non-shivering thermogenesis) was absent in 2-day old pups, it is concluded that it is probably not a primary factor but rather a consequence of the obesity already present in fa/fa pups at 7 days of age.