Hormonal regulation of energy partitioning

A loop system exists between hypothalamic neuropeptide Y (NPY) and peripher al adipose tissue leptin to maintain normal body homeostasis. When hypothal amic NPY levels are increased by fasting or by intracerebroventricular (i.c .v.) infusion, food intake and body weight increase. NPY has genuine hormon e-metabolic effects. It increases insulin and corticosterone secretion rela tive to controls. These hormonal changes, acting singly or combined, favor adipose tissue lipogenic activity, while producing muscle insulin resistanc e. They also promote leptin release from adipose tissue. When infused i.c.v . to normal rats to mimick its central effects, leptin decreases NPY levels , thus food intake and body weight. Leptin i.c.v. has also genuine hormone- metabolic effects. It decreases insulinemia and adipose tissue storage abil ity, enhancing glucose disposal. Leptin increases the expression of uncoupl ing proteins (UCP-1, -2, -3) and thus energy dissipation. Leptin-induced ch anges favor oxidation at the expense of storage. Circadian fluctuations of NPY and leptin levels maintain normal body homeostasis. In animal obesity, defective hypothalamic leptin receptor activation prevent leptin from actin g, with resulting obesity, insulin and leptin resistance.