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.

[Development of energy expenditure in Zucker rats during the first week of life. Effect of time of measurement]. / Evolution des dépenses énergétiques chez le rat Zucker au cours de la première semaine de la vie. Effet de l'heure des mesures.

Gas exchanges were measured in 2, 5 and 7-day old fa/fa and Fa/fa rats for two hours (10.30-12.30 h) at five different temperatures: 35, 33, 30, 28 and 26 degrees C. In 2-day old pups, no significant difference between genotypes was found at either temperatures. At the age of 5 and 7 days, gas exchanges were significantly lower in fa/fa than in Fa/fa pups, but only at temperatures below 33 degrees C. These results differ from those of a previous study where gas exchanges were measured in the afternoon (16.30-18.30 h) (Planche and Joliff, 1985). Thus, our findings show that very early in life there are diurnal variations in the level of gas exchanges according to genotypes. Consequently, estimation of the deficit of energy expenditure in fa/fa rats observed in the present study during the first week of life should be modulated and emphasis laid on the effect of the hour of measurement, even from the early days of life, on the result of metabolic studies.

[Thermogenesis induced by diet in the 2- and 7-day-old Zucker rat]. / La thermogenèse induite par l'alimentation chez le rat Zucker âgé de 2 et 7 jours.

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.

[Development of energy expenditure in the Zucker rat during the first week of life]. / Evolution des dépenses énergétiques du rat Zucker au cours de la première semaine de la vie.

The respiratory CO2 production and O2 consumption of Zucker fa/fa and Fa/fa rats 2, 5 and 7 days old were measured for two hours from 16.30 to 18.30 h. Metabolic studies were performed at five different temperatures: 26, 28, 30, 33 and 35 degrees C. At all the ages studied, maximal energy expenditure was observed at an ambient temperature of 30 degrees C. From the age of 2 days and for all the temperatures studied, except 35 degrees C (thermoneutral temperature), the level of gaseous exchange was statistically lower in fa/fa than in Fa/fa pups. The difference between the two genotypes increased with age. On the other hand, there was no difference in the level of the respiratory quotient between the two genotypes, whatever the age or the temperature. In conclusion, the deficit in energy expenditure of the obese pups, that seemed to be related to a defective thermoregulatory thermogenesis, began very early and was probably a primary manifestation of their genetic defect. It was more than enough to account for their excess fat storage.

Genotype identification of 10-day old Zucker rats by lipid content of inguinal fat pad.

Surgical biopsies of the inguinal fat pad were performed on 35 fa/fa and 40 Fa/fa pups, aged 10 days, from eight litters. The lipid content of the pad, expressed as a percentage of the mean in each litter, allowed a 100 percent reliable prediction of the genotype. In three of the eight litters, we compared this method with that based on the frequency distribution of adipocyte size.

Evidence of a defect in energy expenditure in 7-day-old Zucker rat (fa/fa).

The aim of the investigation was to see whether a defect in energy expenditure could be found in the Zucker rat at the onset of obesity. Obese (fa/fa) and lean (Fa/fa) 7-day-old pups were studied at three ambient temperatures. At 33 degrees C fa/fa pups showed a reduction in oxygen consumption, respiratory CO2 production, in vivo oxidation of injected [1-14C]palmitic acid, as well as in core temperature. When the pups were kept at 28 degrees C, the difference between genotypes was considerably accentuated, thus indicating a subnormal thermogenic response of the fa/fa pups to a mildly cold environment. At 20 degrees C, however, the metabolic rates dropped to the same low level, and the core temperature equilibrated with ambient temperature in both genotypes. The results demonstrate that the 1-wk-old fa/fa pup has a defect in thermoregulatory thermogenesis. The magnitude of the deficit in energy expenditure was more than adequate to account for the 50% greater fat content of 7-day-old fa/fa pups.

[Lipid metabolism in the newborn genetically obese (fa/fa) rat]. / Métabolisme lipidique chez le rat nouveau-né génétiquement obèse (fa/fa).

Compared to its lean litter mate (Fa/--) the Zucker rat (fa/fa) develops obesity without hyperphagia in the first week of lite. It is characterized by adipocyte hypertrophy and higher lipid content in adipose tissue. In vitro utilization as well as in vitro oxidation by diaphragm of palmitic acid was decreased in 1 week old Zucker rat.

Effects of severe diet restriction on the oxygen consumption of obese women during exercise.

Eleven moderately obese, but otherwise healthy, young women were studied for three days while being fed their normal, unrestricted diet and then again for a two week period while being fed an energy-restricted, high-protein diet--220 kcal (0.92 MJ)/day as casein. Oxygen consumption (VO2) was measured 32 times for each subject, both at rest and during bicycle exercises. For each subject oxygen consumption was significantly lower, at rest and during moderate exercise, when the subjects were being fed the restricted diet. There was no significant difference among the diet treatments at the highest activity levels. The explanation proposed (though without experimental proof) is that, during the restricted diet, the increased reverse triiodothyronine (rT3) would result in a decrease of the aerobic glycolysis and no change in the anaerobic glycolysis.