The in vitro secretion of human leptin is gender-dependent but independentof the body mass index of the donors

Objective: Leptin is an adipocyte-secreted hormone acting as a signal to th e central nervous system, where it regulates energy homeostasis and neuroen docrine processes. Leptin plasma levels are mainly regulated by the percent age of body fat, but are also controlled by several metabolic and nutrition al variables. Data regarding leptin secretion suggest that it is gender reg ulated, and higher levels are present in women than men; however the biolog ical basis for this sex-related difference is unknown. To clarify those poi nts, a systematic study with tissue cultures from human omental adipose tis sue was performed. Design and methods: Surgically obtained samples from 137 patients (68 women , 69 men) were evaluated. The assay was standardized in periods of 24 h end ing at 96 h. Each adipose tissue sample from a single donor was incubated i n triplicate and leptin results expressed as the mean of the integrated sec retion into the medium (nanograms of leptin/g tissue per time). Results: Tissue adipose cultures showed a steady leptin secretion throughou t the 96 h studied, with the peak of secretory activity reached at 48 h: af terwards, the in vitro secretion reached a plateau state. Spontaneous lepti n secretion in the 24 h and 48 h period, as well as the area under the curv e analyzed in the 0-48 h period, showed a gender-based difference that was significantly (P < 0.05) higher in women than in men. When data of spontane ous leptin secretion were correlated with tho body mass index (BMI) of the donors, no correlation was found. This suggests that in vivo leptin levels are dependent on the total amount of fat of the individual, but independent of the leptin secretory rate by the adipose tissue of the donor. Conclusions: Leptin secretion from omental adipose tissue in vitro is: (i) significantly higher in samples from women than in samples from men: and (i i) not correlated with the BR II, showing that in vitro leptin secretion is not related to the adiposity of the donor.