Endocrine basis for weight gain after fasting or VMH lesion in rats

To study some hormonal and metabolic factors contributing to the regulation of body fat mass, food intake, and the circadian lipogenesis-lipolysis pattern, insulin and glucose responses to intravenous glucose loads were measured in both phases of the light-dark cycle in two groups of rats considered to be below their level of body fat mass regulation [rats with lesion of the ventromedial hypothalamus nuclei (VMH) in the "dynamic" phase of obesity and food-restricted rats during the refeeding phase] compared with the responses of two other groups at this level (VMH-lesioned rats in "static" phase and normal rats). Glucose tolerance and insulin release were greater during the dynamic phase and to a lesser degree during refeeding than during the static phase and normal feeding. The differences between night and day found in normal rats disappeared in dynamic and refed animals and reappeared at the level of static phase. Thus the normal circadian hormonal metabolic patterns responsible for increased lipogenesis and relative hyperphagia during the night and lipolysis with hypophagia during the day were lost in rats below their level of body fat mass regulation and were reinstated in animals on returning to this level.