Ventromedial hypothalamic knife-cut lesions in rats resistant to dietary obesity

The effects of ventromedial hypothalamic (VMH) knife-cut lesions on food intake and body weight of S 5B/Pl rats, which are normally resistant to obesity when eating a high-fat diet, were examined in two experiments. In the first experiment body weight increased only slightly after VMH knife-cut lesions when animals were fed pelleted laboratory chow or a 10% corn oil diet. When eating the 30% corn oil diet, however, body weight increased in the VMH knife-cut rats. In the second experiment VMH knife-cut lesions produced a small weight gain in rats fed the 10% fat diet; this manipulation also increased food intake and disrupted the normal diurnal feeding pattern. Changes in the weight of the liver, interscapular brown adipose tissue, and white adipose tissue paralleled the changes in body weight. Plasma insulin increased in the rats eating the 30% corn oil diet ad libitum but not in the VMH-lesioned animals pair fed to the sham-operated rats. Incorporation of 3H from 3H2O into lipid was significantly increased in white fat of animals with VMH knife cuts. Similar results were obtained from incubation of adipose tissue in vitro with insulin and radioactively labeled glucose. These studies show that hypothalamic knife-cut lesions can remove the resistance of the S 5B/Pl rats to obesity when they are fed a high-fat diet.