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.