Impaired hypophagia induced by fecal anorexigenic substance in Zucker obese rats

Influence of fecal anorexigenic substance (FS-T) on feeding by Zucker obese rats was compared to that by their lean littermates and Wistar King A rats. FS-T, which has been found to suppress food intake mainly by activation of glucoreceptor neurons in the ventromedial hypothalamus, was injected intraperitoneally in a dose of 7 U/kg at 1930 hr, immediately before the dark period. Potency of FS-T in feeding suppression was much less in the obese rats than in their lean littermates or the Wistar King A rats. Meal size of the obese rats was decreased after the injection, but meal duration was unaffected. The suppressive effect on the lean rats and the Wistar King A rats included decrease of both size and duration of the meal. These results suggest that chemosensitivity in the ventromedial hypothalamus of Zucker obese rats may be impaired, which may be one explanation of the obesity in Zucker obese rats.