Modulation of the satiating effect of amylin by central ghrelin, leptin and insulin

Amylin is a pancreatic hormone that is considered to be a satiating signal acting on neurons of the area postrema (AP) in the hindbrain. The adiposity signals leptin and insulin act in the hypothalamus to influence feeding. They also enhance the hindbrain's responsivity to satiating signals, e.g. cholecystokinin (CCK). The orexigenic hormone ghrelin is thought to use the same hypothalamic pathways as leptin and insulin, with opposite actions on feeding behaviour. In fact, CCK and ghrelin also seem to interact in the control of feeding. Because CCK's anorectic effect depends on endogenous amylin, the aim of this study was therefore to evaluate a possible functional interaction between amylin and these hormones on short-term food intake in rats. The experiments were performed with male Wistar rats. Intracerebroventricular injection (i3vt) of an orexigenic dose of ghrelin (5 ng/5 microl) reduced but did not completely reverse the intraperitoneal amylin (5 microg/kg)-induced inhibition of food intake. In comparison, administration of a sub-threshold dose of ghrelin (3 ng/5 microl) did not affect the anorexigenic action of peripheral amylin. Leptin administered into the third ventricle (i3vt; 3.5 microg/5 microl) and intraperitoneal amylin (5 microg/kg) synergistically reduced food intake in chow-fed rats. I3vt insulin, administered at a sub-threshold dose (0.5 mU/5 microl), significantly enhanced the response to peripheral amylin. These results indicate that the lipostatic signals leptin and insulin may synergize with amylin to reduce food intake. In contrast, under the conditions tested, the orexigenic hormone ghrelin does not seem to influence the feeding response to peripheral amylin.