Amylin: a novel action in the brain to reduce body weight

Amylin is a 37-amino acid peptide hormone that is co-secreted with insulin by pancreatic B cells in response to a nutrient stimulus (e.g., during meals). To test the hypothesis that amylin acts within the brain to reduce long-term food intake and body weight, we examined the effects of acute and chronic 3rd-ventricular (i3vt) infusion of low doses of amylin on food intake and body weight in rats. In one experiment, separate groups of ad lib-fed male Long Evans rats were given one i3vt infusion (3 microl over 30 s) of synthetic cerebrospinal fluid vehicle or 1 to 100 pmol amylin, and food intake and body weight were monitored for 7 days. Amylin potently and dose-dependently reduced 1-h food intake, with all doses producing significant reductions. The largest dose (100 pmol) significantly reduced 24-h intake by over 30%. The effect was persistent in that both 7-day cumulative food intake and body weight change were significantly decreased over the 7 days following a single injection of 100 pmol of amylin. Other groups of rats received continuous i3vt infusion (0.5 microl/h volume) of saline or 2.0 pmol/h amylin via osmotic minipumps over 10 days. Food intake over the 10-day infusion was significantly suppressed in amylin-treated rats as compared to that of controls. Consequently, by the 4th day of infusion, amylin rats weighed significantly less than baseline relative to saline controls, and this difference persisted throughout the remainder of the infusion period. At sacrifice (Day 10), the percent of body weight from retroperitoneal fat depots was significantly lower in the amylin-treated rats, indicative of a reduction of total body adiposity. In summary, the results support the hypothesis that amylin acts as a signal to the brain contributing to the maintenance of long-term energy balance.