Effects of protein and energy on dietary selection and protein utilization in rats with ventromedial hypothalamic lesions.

The effect of bilateral destruction of the ventromedial hypothalamus (VMH) on protein and energy intakes was examined in relation to protein utilization. In Experiment 1, rats with VMH lesions were allowed to select protein (either casein or wheat gluten) and energy from two diets containing 70% and 5% protein, respectively. In Experiment 2, they were restricted to 0, 100 and 200 mg N/day of protein and given free access to protein-free diet. In Experiment 3, they were restricted to 2 and 5 g/day of protein-free diet but given 92% protein diet ad libitum. Self-selecting rats with VMH lesions consumed about 100 kcal/day regardless of the protein source, in contrast to sham-operated controls which consumed 75 kcal/day. They showed increased non-protein energy intake with constant protein consumption resulting in normal protein retention with increased body fat. When protein intake was restricted to 200 mg N/day, energy intake was reduced in animals given diet containing wheat gluten more than in those given diet containing casein, resulting in lower protein utilization. Therefore, food intake depended upon the amount of dietary protein. Rats with VMH lesions showed an exaggerated response to the ratio of protein to energy in the diet and consumed more energy from balanced diet but showed more reduction in food intake than controls in response to diet with an inappropriate ratio of protein to energy. The present study confirmed that the VMH was related to regulation of energy intake but not protein intake. It is suggested that protein intake is regulated in relation to maintenance of body protein in rats with VMH lesions as well as in normal rats.