Pre-beta-HDL stimulates placental lactogen release from human trophoblast cells

To examine whether pre-beta-high-density lipoprotein (HDL) may be involved in regulation of human placental lactogen (hPL) release, pre-beta-HDL was i solated from term pregnancy serum, and the effect of purified pre-beta-HDL on hPL release from trophoblast cells was examined after 1 h of exposure. P re-beta-HDL stimulated a dose-dependent increase in hPL release with half-m aximal stimulation at a dose of 300-400 mu g/ml, which is within the normal physiological range during pregnancy. Analysis of pre-beta-HDL and alpha-H DL in serum from pregnant women at different stages of gestation (determine d by Western blot analysis) indicated that the pre-beta-HDL-to-alpha HDL ra tio increased linearly after the 10th week of gestation (r = 0.88, P < 0.00 1), reaching a maximum sixfold greater than that of nonpregnant women. The increase in serum pre-beta-HDL during pregnancy paralleled that of plasma h PL concentrations (r = 0.93, P < 0.001). Two-dimensional electrophoresis in dicated that the increase in pre-beta-HDL was due primarily to an increase in pre-beta(1)-HDL and pre-beta(2)-HDL, two of the three forms of pre-beta- HDL present in blood. These results suggest a role for pre-beta-HDL in the regulation of hPL expression during pregnancy.