Meal patterns and body weight changes during insulin hyperphagia and postinsulin hypophagia

Abstract

Changes in food intake, body weight, and meal patterns brought about by repeated injections of insulin were investigated. Male Sprague—Dawley albino rats were subcutaneously injected with slow-acting insulin twice daily for 3 days, 4 IU/injection on Day 1 and 6 IU/injection thereafter. Food intake and body weight were increased by the injections. Hyperphagia was most marked during the bright phase of the lighting cycle. Meal frequency increased during both lighting phases and nocturnal meal duration decreased, resulting in disappearance of the normal circadian rhythmicity of feeding. Postinsulin, food intake and body weight decreased. Body weight returned to control levels within 48 hr after insulin treatment, although the net hypophagia during this time failed to match the degree of the preceding hyperphagia. Postinsulin hypophagia, manifested primarily as a reduction in meal duration, was evident in both lighting phases. The data suggest that both behavioral and metabolic adaptations contribute to the renormalization of body weight following insulin treatments and that different controls of food intake operate during insulin hyperphagia and postinsulin hypophagia.