Body fat mass, leptin and puberty

Leptin, the ob gene product, provides a molecular basis for the lipostatic theory of the regulation of energy balance, Leptin circulates as a monomeri c 16 kDa protein in rodent and human plasma and is also bound to leptin bin ding proteins that may form large high molecular weight complexes. Initial models of leptin action included leptin-deficient ob/ob mice and leptin-ins ensitive db/db mice. Peripheral or central administration of leptin reduced body weight, adiposity, and food intake in ob/ob mice but not in db/db mic e, In ob/ob mice leptin treatment restored fertility. Leptin interacts with many messenger molecules in the brain. For example, leptin suppresses neur opeptide Y (NPY) expression in the arcuate nucleus. Increased NPY activity has an inhibitory effect on the gonadotropin axis and represents a direct m echanism for inhibiting sexual maturation and reproductive function in cond itions of food restriction and/or energy expenditure. By modulating the hyp othalamo-pituitary-gonadal axis both directly and indirectly, leptin may th us serve as the signal from fat to the brain about the adequacy of fat stor es for pubertal development and reproduction, Normal leptin secretion is ne cessary for normal reproductive function to proceed and leptin may be a sig nal allowing for the point of initiation of and progression toward puberty.