Pair-feeding of sham-operated controls to rats with dorsomedial hypothalamic lesions: new evidence for an 'organismic' set point.

Weanling male Sprague-Dawley rats received electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL rats) and sham operations, respectively, and were maintained on lab chow ad libitum for 23 days (Expt. 1) and 55 days (Expt. 2). Following this period, one group of sham-operated controls was pair-fed to the DMNL rats, which were hypophagic compared to a second sham-operated group that was fed ad libitum. This period lasted 27 days (Expt. 1) and 24 days (Expt. 2). Although pair-fed controls were heavier than DMNL rats, they showed normal food utilization (EFU) in Expt. 1 and reduced EFU in Expt. 2. Pair-fed controls also had decreased carcass fat, hypoglycemia, hypoinsulinemia, hypotriglyceridemia and enhanced in vitro epididymal fat pad glucose oxidation when compared to DMNL rats. These data suggest that pair-fed controls cannot cope as efficiently with the reduced influx of substrate as do DMNL rats. Evidently, the reduced amount of food that DMNL rats spontaneously eat is adequate for their reduced body size, whereas this is not the case in the pair-fed controls. This is taken as evidence for a harmonious readjustment by DMN lesions of both body size and food intake and the underlying homeostatic processes and supports our concept of an 'organismic' set point that has been released by the DMN lesions.