Dorsomedial hypothalamic hypophagia: Self-selection of diets and macronutrients, efficiency of food utilization, “stress eating”, response to high-protein diet and circulating substrate concentrations

Abstract

Compared to sham-operated controls, male weanling rats with bilateral dorsomedial hypothalamic lesions (DMNL rats) showed hypophagia, reduced ponderal and linear growth, normal body composition and decreased efficiency of food utilization (EFU) two weeks after the hypothalamic operation. Subsequently, all animals were given a choice between three equicaloric diets with different macronutrient content for a period of 31 days. DMNL rats selected significantly less high-fat (HFD) and high-protein (HPD) diet than controls, but in percent of total intake, they selected only less from the HPD. DMNL rats consumed less of all three macronutrients than the controls, but in percent of total calories consumed, their intake was comparable to that of the controls; the EFU during this period was normal. Tail pinch (TP) stress did not result in hyperphagia, nor in a macronutrient choice different from the non-TP rats. However, TP caused reduced EFU and linear growth irrespective of hypothalamic damage, suggesting a stress response. During the 25-day availability of a HPD (43.2%), both DMNL rats and controls ate amounts of macronutrients comparable to the self-selection experiment. Although the DMNL rats were hypophagic in comparison with the controls, they ate more protein than in the self-selection experiment because of the higher protein content of the diet. Thus, DMNL rats will eat more protein when other macronutrients are limited. In both fed and 48h-fasted rats, there was no significant alteration in plasma glucose, glycerol, and total protein that could be related to the DMN lesions. It is concluded that the DMNL rat, despite its dramatically reduced size and energy intake, has not lost the capacity to select macronutrients for normal growth and health within the framework of its reduced somatic-metabolic potential.