Abnormalities of leptin and ghrelin regulation in obesity-prone juvenile rats

Rats selectively bred to develop diet-induced obesity (DIO) spontaneously gain more body weight between 5 and 7 wk of age than do those bred to be diet resistant (DR). Here, chow-fed DIO rats ate 9% more and gained 19% more body weight from 5 to 6 wk of age than did DR rats but had comparable leptin and insulin levels. However, 6-wk-old DIO rats had 29% lower plasma ghrelin levels at dark onset but equivalent levels 6 h later compared with DR rats. When subsequently fed a high-energy (HE; 31% fat) diet for 10 days, DIO rats ate 70% more, gained more body and adipose depot weight, had higher leptin and insulin levels, and had 22% lower feed efficiency than DR rats fed HE diet. In DIO rats on HE diet, leptin levels increased significantly at 3 days followed by increased insulin levels at 7 days. These altered DIO leptin and ghrelin responses were associated with 10% lower leptin receptor mRNA expression in the arcuate (ARC), dorsomedial (DMN), and ventromedial hypothalamic nuclei and 13 and 15% lower ghrelin receptor (GHS-R) mRNA expression in the ARC and DMN than in the DR rats. These data suggest that increased ghrelin signaling is not a proximate cause of DIO, whereas reduced leptin sensitivity might play a causal role.