Comment

Leptin, a 167 amino acid protein transcribed from theob gene, was originally described as a hormone secreted specifically by adipocytes, that is involved in the central regulation of food intake and energy expenditure.1Circulating concentrations of leptin show a strong positive correlation with fat mass. Leptin acts on the hypothalamus of the brain to regulate body weight by decreasing food intake and increasing physical activity and energy expenditure.2 Theob/ob mouse has a recessive mutation of theob gene which results in absence of circulating leptin leading to hyperphagia, reduced energy expenditure and development of obesity. Subsequent work has shown that leptin, in addition to its role in metabolic control, has important roles in reproduction and neuroendocrine signalling. Both animals and humans with leptin deficiency have increased circulating corticosterone concentrations, reduced thyroxine concentrations, and infertility due to hypogonadotrophic hypogonadism.3 ,4 In theob/ob mouse these changes are reversed by administration of exogenous leptin.4

Contrary to initial reports, leptin is not produced exclusively by fat cells. Glucose and free fatty acids increase leptin expression and …