Estrogen upregulates nitric oxide synthase expression in cultured rat hepatic sinusoidal endothelial cells

Background/Aims: Estrogen receptor (ER) is present in vascular endothelial cells and estrogen promotes nitric oxide (NO) synthesis, which relaxes smoo th muscle cells. It is also speculated that NO is synthesized by estrogen i n hepatic sinusoidal endothelial cells (SECs). Here we investigated the loc alization of ER and endothelial cell nitric oxide synthase (ecNOS), and det ermined 17 beta -estradiol (E2)-induced ecNOS expression in normal rat SECs . Methods: Cultured SECs were used. Fluorescence intensities of ecNOS were me asured by immunofluorescence using a confocal laser-scanning microscope. E2 was added (100 pg/ml) to the culture medium, and the expressions of ecNOS mRNA and protein were analyzed by reverse-transcription polymerase chain re action and Western blotting. NO production in cultured SECs was examined us ing diaminofluorescein-2 diacetate as a fluorescent indicator for NO. Results: Immunolocalization of ER and ecNOS in normal liver was demonstrate d in endothelial cells lining the hepatic sinusoids, ER and ecNOS were loca lized in the nuclei and cytoplasm of cultured SECs, respectively. The mRNA expression of ecNOS in cultured SECs was increased after 6 h, and the prote in expression of ecNOS was increased 24 h after E2 stimulation. The fluores cence intensity of NO in cultured SECs was increased by E2 stimulation comp ared with untreated control cells. Conclusions: These results suggested that ER is present in SECs, and estrog en upregulates NO production in SECs, E2 mag he involved in the regulation of the hepatic sinusoidal microcirculation. (C) 2001 European Association f or the Study of the Liver. Published by Elsevier Science B.V. All rights re served.