Leanness of Lou/C rats does not require higher thermogenic capacity of brown adipose tissue.

Lou/C rats, an inbred strain of Wistar origin, remain lean throughout life and therefore represent a remarkable model of obesity resistance. To date, the exact mechanisms responsible for the leanness of Lou/C rats remain unknown. The aim of the present study was to investigate whether the leanness of Lou/C rats relies on increased thermogenic capacities in brown adipose tissue (BAT). Results showed that although daily energy expenditure was higher in Lou/C than in Wistar rats, BAT thermogenic capacity was not enhanced in Lou/C rats kept at thermoneutrality as demonstrated by reduced thermogenic response to norepinephrine in vivo, similar oxidative activity of BAT isolated mitochondria in vitro, similar levels of UCP1 mRNA and lower abundance of UCP1 protein in interscapular BAT depots. Relative abundance of ß3-adrenergic receptor mRNA was lower in Lou/C BAT while that of GLUT4, FABP or CPT1 was not altered. Activity-related energy expenditure was however considerably increased at thermoneutrality as Lou/C rats demonstrated an impressively high spontaneous running activity in voluntary running wheels. Prolonged cold-exposure (4 °C) depressed the spontaneous running activity of Lou/C rats while BAT thermogenic capacity was increased as reflected by rises in BAT mass, oxidative activity and UCP1 expression. It is concluded that the leanness of Lou/C rats cannot be ascribed to higher thermogenic capacity of brown fat but rather to, at least in part, increased locomotor activity. BAT is not deficient in this rat strain as it can be stimulated by cold exposure when locomotor activity is reduced suggesting some substitution between these thermogenic processes.

Metabolic characteristics and body composition in a model of anti-obese rats (Lou/C).

OBJECTIVE: The aims of this study were to investigate some features of the metabolic profile and the body composition of male Lou/C rats and to examine whether these characteristics are strictly related to the food-intake reduction. RESEARCH METHODS AND PROCEDURES: Fourteen-week-old male Lou/C rats were compared with age-matched male Wistar rats fed ad libitum (WAL) and another group of male Wistar rats whose food was chronically restricted (WFR) to the same amount as the Lou/C rats from weeks 3 to 14. RESULTS: Food intake and body weight were significantly (p < 0.01) reduced in Lou/C compared with WAL rats, whereas these reductions were perfectly reproduced in WFR rats. Lou/C rats demonstrated lower relative weights of retroperitoneal (0.97 +/- 0.07 vs. 1.67 +/- 0.16 and 1.88 +/- 0.15 g/100 g body) and epididymal (1.01 +/- 0.02 vs. 1.62 +/- 0.12 and 1.80 +/- 0.11 g/100g body) fat depots than did the two other groups and no decrease in the percentage of carcass proteins, which was observed in the WFR rats. In addition, compared with the WFR group, the Lou/C rats showed lower plasma glucose levels (3.65 +/- 0.14 vs. 4.72 +/- 0.15 and 4.7 +/- 0.19 mM); a tendency (p < 0.1) for lower liver glycogen concentrations; and similar levels of glycerol, free fatty acids, and beta-hydroxybutyrate concentrations. Epinephrine and the relative weight of the adrenal glands were significantly (p < 0.01) lower in the Lou/C rats than in the WAL rats and the two other groups, respectively. DISCUSSION: The ability of the Lou/C rats to accumulate less body fat than their equally food-restricted Wistar counterparts (WFR) suggests a difference in basal metabolism in this strain of rats that resembles obesity-resistant rats.