To investigate whether the administration of transdermal estradiol is capable of modifying circulating levels of leptin.
Forty postmenopausal women randomly received in a double-blind fashion, a transdermal patch containing either placebo or estradiol (50 μg/day). After 2 months of treatment, they were switched to the alternate treatment for another 2 months. Leptin levels were measured at the end of the placebo and estradiol administration. In a subset of 28 women an evaluation of body composition via bioelectrical impedance and an oral glucose tolerance test (OGTT; 75 g) were also performed at the end of the placebo and estradiol administration. Glucose, insulin, and leptin levels were measured in all OGTT samples.
Leptin levels were related directly to body mass index (BMI), fat mass, and insulin, and inversely related to lean mass. In comparison to placebo, transdermal estradiol increased estradiol (from 77.8 ± 8.4 pmol/l to 183.1 ± 20.9 pmol/l;p < 0.0001) but did not significantly modify leptin (19.1 ± 2.4 μg/l vs. 18.6 ± 2 μg/l) or BMI. Estradiol did not modify fat mass or lean mass, significantly increased intracellular water (31.1 ± 0.7% vs. 37.2 ± 2.3%, p < 0.05), and decreased extracellular water (40.5 ± 0.7% vs. 36.3 ± 1.7%;p < 0.04). Leptin did not increase during OGTT, but a significant decrease, linearly related to BMI (r = 0.519;p = 0.0189), was observed at the end of the test.
Low doses of transdermal estradiol exert no influence on fasting leptin levels or BMI. The possibility that different doses of estradiol exert a more pronounced effect on circulating leptin needs to be addressed in comparative studies.