Insulin infusion during a nocturnal fast suppresses the subsequent day-time intake

Much recent evidence suggests a dual and opposite action of insulin on food intake and body weight. Peripherally administered, long acting insulin stimulates weight gain and food intake. On the contrary intracerebroventricularly infused insulin decreases food intake and body weight. It has been suggested that the shift from the nocturnal hyperinsulinism and hyperphagia to the day-time hypoinsulinism and hypophagia depended on the action of insulin on the brain during the night. It has also been hypothesized that the absence of nocturnal hyperinsulinism due to fasting was partly responsible for the hyperphagia observed during the subsequent day-time. In the present experiment, insulin was infused intravenously at various low doses (0.01, 0.025, 0.05 U/hr) during a nocturnal fast. Its effects on the following diurnal free food intake were investigated. It was shown that the experimentally elevated plasma insulin induced a dose-dependent reduction in the day-time feeding response. It was concluded that this reduction is due to the chronic action on the brain of the high plasma insulin level induced by the infusion during the nocturnal fast.