Energy expenditure and adipose tissue development in 2- to 8-day-old Zucker rats.

We investigated a possible relationship between impaired energy expenditure and the development of obesity in Zucker fa/fa pups in the first week of life; 19 fa/fa and 16 Fa/fa pups from four litters were studied. Gas exchanges were measured at 30 degrees C, from 17.00 to 18.00 hours, at the ages of 2, 5 and 7 days. At days 3, 6 and 8, a partial biopsy of inguinal adipose tissue was performed in the morning and used for determination of cellularity and TG content. At all ages studied, the level of gas exchange was significantly higher in Fa/fa than in fa/fa pups. At 5 and 7 days, but not at 2 days, adipose cell volume and triglyceride content were significantly higher in fa/fa than in Fa/fa pups, and a significant negative correlation was found between the level of O2 consumption and the volume of adipocytes. These results confirm the importance of the energy expenditure defect, which is present in fa/fa pups before the overdevelopment of adipose tissue, in the onset and development of this genetic obesity.