The adipose tissue secretes different hormones called adipocytokines. Their secretion seems to vary in relation to the amount of adipose tissue accumulated, although the exact mechanism is not known. During profound weight loss, as in anorexia nervosa, there is a marked decrease in the adipose tissue mass with the typical changes in adipocytokines secretion that occur in these circumstances. One of the most studied adipocytokine changes is decreased leptin secretion. Increased fat mass stores are accompanied by an increased leptin secretion; decreased fat mass stores decrease leptin secretion. Low serum levels of leptin reaching the hypothalamus increase the activity of the 'hunger center,' in part by increasing the local activity of neuropeptide Y. Individuals with anorexia nervosa have very low levels of leptin in blood and cerebrospinal fluid, in relation to their decreased adipose tissue. This should cause an increase in hypothalamic neuropep-tide Y content and hunger, but this compensatory mechanism to maintain a normal body weight does not seem to be effective in anorexic patients. Another important effect of the serum levels of leptin on the hypothalamus is the modulation of the gonadal axis. Low levels of leptin are associated with decreased activity of the gonadal axis, and this explains the relationship between starvation and hypogonadism. After nutritional rescue and weight regain, the levels of leptin in the serum become normal.
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