Leptin concentrations in serum from a randomly recruited sample of 50- to 80-year-old men and women: positive association with plasma insulin-like growth factors (IGFs) and IGF-binding protein-3 in lean, but not in obese, individuals

Objective: The GH/IGF axis is thought to play an important role in the regulation of body composition throughout life. Changes in body fat stores also affect the activity of the GHI/IGF axis, but the mechanisms whereby body fat status is signaled to the GH/IGF axis are poorly understood. The newly discovered protein leptin is exclusively produced by adipocytes, and circulating concentrations of leptin closely reflect body fat stores. Design: We here examined whether leptin might be associated with the activity of the GH/IGF axis in a population-based sample, Patients and methods: Circulating concentrations of leptin, IGF-I, IGF-II, and insulin-like growth factor-binding protein-3 (IGFBP-3) were measured in a population-based sample of 50-to 80-year-old men (n = 217) and women (n = 198) by specific RIA. Results: All three IGF components were significantly positively correlated with leptin in lean women (body mass index (BMI) <25 IGF-II). IGF-II was also positively correlated with leptin in lean men, and positive correlation of leptin with IGF-I in lean men was of borderline statistical significance, In contrast, no correlation was observed in moderately overweight (BMI 25-30kg/m(2)) and obese individuals (BMI > 30kg/m(2)). Conclusion: Our study shows that serum leptin concentrations are significantly associated with circulating IGF components in lean elderly subjects. The precise mechanism of this interaction between leptin and the GH/IGF system remains to be determined.