Somatic, metabolic and endocrine correlates of set point recovery in food-restricted and ad lib-fed weanling rats with dorsomedial hypothalamic lesions

Abstract

Male Sprague-Dawley rats received either electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL rats) or sham-operations (CON), and were fed lab chow ad lib for 41 post-operative (POP) days. Subsequently one lesioned (DNML-AL) and one control group (CON-AL) continued to receive lab chow ad lib until the end of the experiment (POP day 78). A second lesioned (DMNL-RE) and control group (CON-RE) were given 80% of the amount of food eaten by their ad lib-fed counterparts for 28 days. At this time several rats from each group were killed. The remaining animals were then given lab chow ad lib for nine days and then also killed. Both DMNL-RE and CON-RE recovered their lowered body weight, food intake and feeding efficiency and showed the same pattern and relative magnitude as their ad lib-fed counterparts. Similarly, carcass lipid, epididymal fat pad lipid, incorporation of glucose-U-C14 into fat pad saponifiable lipid, total lipid, total glycogen (DPM/protein), liver protein, incorporation of glucose into liver CO2 and concentrations of plasma glucose, glycerol, triglycerides and free fatty acids normalized on refeeding to the same extent and in the same pattern in DMNL-RE as in CON-RE. In contrast to previous studies, plasma insulin was lower in DMNL-AL than in CON-AL but DMNL-RE and CON-RE had similar levels on refeeding. Also on refeeding, both DMNL-RE and CON-RE showed the same enhanced glucose incorporation into liver total lipid. The data show that DMNL rats, although smaller in size and hypophagic in absolute terms, recovered lost body weight--at least under our relative mild reduction of 80% of their ad lib-fed controls--with the same competence and in the same time interval as sham-operated controls. It is quite possible that a more severe restriction of body weight would have uncovered some deficits in DMNL rats, however. Under the constraints of the present experimental arrangement, the data strengthen previous evidence for the existence in DMNL rats of an "organismic" set point that makes for a "scaled-down" but homeostatically normal animal.