Rats maintained on high-fat diets exhibit reduced satiety in response to CCK and bombesin

Rats maintained on high-fat diets often exhibit increased food intake and weight gain. We hypothesized that high-fat diets might result in reduced sensitivity to hormonal signals responsible for terminating food intake--satiety signals. The intestinal hormone cholecystokinin (CCK) and the gastrointestinal neuropeptide, bombesin (BBS) both have been proposed as satiety signals. To determine whether maintenance on high-fat diets alters sensitivity to satiating effects of CCK and bombesin (BBS), rats were maintained on a low fat diet (LF), a high-fat diet that was isocaloric with the low-fat diet (HF), or one of two hypercaloric high-fat diets (HF-1, HF-2) that differed from HF and LF in fat, fiber, and total caloric content. CCK and bombesin reduced food intake significantly less in rats maintained on high-fat diets, compared to those on the low fat diet. Neither high caloric intake, which was associated with increased body weight gain on the two hypercaloric diets, nor fiber content of the diet accounted for the reduced response of HF rats to CCK. Rather, reduced sensitivity to CCK was related only to the high proportion of calories taken as fat. We also determined whether reduced CCK sensitivity was due to the maintenance on a particular diet or to the diet eaten during a CCK test. After CCK, rats maintained on LF reduced food intake more (49%) than rats maintained on HF (22%), regardless of whether they ate HF or LF during the CCK test itself. These findings indicate that maintenance of rats on high-fat diets reduces sensitivity to some peptide satiety signals. Reduced sensitivity to satiety signals might contribute to overeating and obesity often observed when rats are maintained on high-fat diets.