Figure 4.

Responses to quantitative changes in leptin level. Different biological responses to leptin are observed at different plasma concentrations. The complete absence of leptin leads to a markedly abnormal phenotype. Slightly subnormal levels ameliorate many of the features of leptin-deficient animals but is associated with cold intolerance and moderate obesity. Finally, physiologic increases in leptin levels decrease body fat. The molecular basis for the different physiologic responses elicited at various leptin concentration is not known.