Estrogen increases the levels of a protein called apolipoprotein M in the body by acting through a specific receptor. This was shown by studying the effects of estrogen on liver cells and female rats. When estrogen was given to the rats, their levels of apolipoprotein M and other lipids in the blood increased. This effect was blocked when an estrogen receptor antagonist was used. The findings suggest that estrogen can boost the production of apolipoprotein M through its receptor, which may have implications for lipid metabolism in the body.