Participation of high-density lipoprotein in vitellogenesis in Japanese eel hepatocytes

To investigate effect of estradiol-17β (E2) treatment in vivo on binding of eel hepatocytes to HDL, we developed hepatocytes binding assay. When hepatocytes were incubated with 200 times excess of eel HDL, the binding of hepatocytes to HDL precoated on wells was inhibited competitively. This indicates that eel hepatocytes bound specifically to HDL. E2 treatment in vivo induced vitellogenin (VTG) synthesis. Hepatocytes prepared from the same E2 treatment eel showed 3-fold higher ability of binding to HDL compared to hepatocytes prepared from ells without E2 treatment. We also examined effects of E2 and HDL on VTG induction in cultured hepatocytes. VTG, determined by enzyme-linked immunosorbent assay (ELISA), induction was about two-times higher in the presence of both 10−5 M of E2 and 400 μg of HDL than in the presence of 10−5 M E2 alone. At concentrations below 10−6 M E2, VTG was not induced in the presence or absence of HDL. By SDS-PAGE and immunoblotting, VTG was detected only in the presence of both 10−5 M of E2 and HDL. Our findings strongly support the idea that HDL correlates with vitellogenesis in eel liver.