Hypothalamus and brown fat: white and brown adipose tissue lipolysis in weanling rats with dorsomedial hypothalamic lesions.

Weanling male Sprague-Dawley rats received bilateral electrolytic lesions in the dorsomedial hypothalamic nuclei (DMN); sham-operated animals served as controls. The animals were fed lab chow and given tap water ad libitum. Fourteen days after the hypothalamic operation they were weighed and measured to assess ponderal and linear growth gains and Lee Index and were sacrificed on the following day. Body weight, body weight gain over two weeks, nose-tail length and gain in nose-tail length, and food intake were all highly significantly reduced in DMNL rats in comparison with controls. Lee Index and efficiency of food utilization were normal, however. Epididymal fat pads weighed less in both absolute and relative (percentage body weight) terms than in controls. Basal lipolysis was increased and epinephrine-stimulated lipolysis was decreased in DMNL rats, as was the protein content of the epididymal fat pads. Lipid content was normal, however. Interscapular brown adipose tissue (BAT) was significantly lighter in DMNL rats than in controls in absolute terms, but all other parameters measured were normal, as were plasma glucose, glycerol, and free fatty acids. Comparison with results from rats that received ventromedial hypothalamic lesions shortly after weaning indicates a differential effect in most epididymal fat pad parameters but similarities to changes in BAT. These data add to previous demonstrations of normal responses to homeostatic challenges in the growth-retarded, hypophagic-hypodipsic rat with lesions in the dorsomedial hypothalamic nucleus.