We measured bound and free
leptin levels in preeclamptic and matched normal pregnant and never-pregnant women to determine whether the free component of
leptin is increased during pregnancy and further increased in
preeclampsia. Two milliliters of serum was obtained from 18 normal and 18 preeclamptic patients matched by pre-pregnancy body mass index (BMI), and from 18 never-pregnant women matched by BMI with the pregnant groups. The sample was subjected to gel filtration using
Sephadex G-100. Radioimmunoassay (RIA) was performed on all fractions, and the proportions of bound and free
leptin were determined by analyzing the areas under the curve of the chromatographic profile. The total maternal serum
leptin concentration was significantly higher in normal pregnancy compared with the nonpregnant state and was further increased in
preeclampsia (33.8 +/- 4.1 v 15.2 +/- 1.8 ng/mL, P = .002, and 48.1 +/- 5.6 ng/mL, P = .02, respectively). Free
leptin was increased in normal pregnant compared with never-pregnant women (25.9 +/- 4.1 v 11.0 +/- 2.0 ng/mL, respectively, P = .01), while the increase of total
leptin in
preeclampsia was exclusively in the free fraction that was significantly higher versus the normal pregnant group (41.8 +/- 5.6 v25.9 +/- 4.1 ng/mL, respectively, P = .01). The bound
leptin fraction, by contrast, was significantly increased in the normal pregnant group compared with the preeclamptic group and the never-pregnant group (7.9 +/- 0.56 v 6.2 +/- 0.36 and 4.1 +/- 0.36 ng/mL, respectively, P = .009 and P = <.0001). In conclusion, the free
leptin concentration increases in normal pregnancy and is further increased in
preeclampsia. This supports the hypothesis that biologically active
leptin is elevated in normal pregnancy and is increased more in women with
preeclampsia.