CELLULAR-LOCALIZATION OF ENDOTHELIN-1 AND INCREASED PRODUCTION IN LIVER-INJURY IN THE RAT - POTENTIAL FOR AUTOCRINE AND PARACRINE EFFECTS ON STELLATE CELLS

Endothelin (ET) peptides have been implicated in the pathogenesis of s everal biological processes within the liver. ET levels are elevated i n the circulation of patients with cirrhosis, and recent data suggest that ET may be overproduced in the liver itself in this condition, The aims of the current study were to elucidate the cellular source and e xpression of endothelin-1 (ET-1) in normal and injured liver, and to i nvestigate its biological effects on stellate cells, the primary targe t of ETs in the liver. In normal hepatic cells, preproET-1 messenger R NA (mRNA) was detected in only nonparenchymal cells, predominantly in sinusoidal endothelial cells, After biliary fibrosis and early cirrhos is induced by bile duct ligation, preproET-1 mRNA and immunoreactive E T levels increased, with progressiive injury in whole liver extracts, as well as in isolated stellate and endothelial cell fractions. Eight days after bile duct ligation, the relative increase in preproET-1 mRN A was 1.6- and 7.6-fold above normal in sinusoidal endothelial and ste llate cells, respectively. Additionally, immunoreactive ET peptide lev els increased by 60% +/- 27% over basal values in sinusoidal endotheli al cells and 98% +/- 40% in stellate cells. Cultured stellate cells re sponded dramatically to exogenous ET-1 by the spreading and up-regulat ion of smooth muscle alpha actin expression. Furthermore, in early cul ture before cellular activation, ET-1 (10 nmol/L) caused over a twofol d increase in [H-3]thymidine incorporation, while activated cells (i.e ., those cultured for >1 week) exposed to ET-1 exhibited up to a fivef old decrease in [H-3]thymidine incorporation. The data indicate that n ot only is ET-1 overproduced by both sinusoidal endothelial and stella te cells during liver injury, but that it also has potent effects on f eatures of stellate cell activation. We conclude that autocrine and pa racrine production of ET-1 is prominent and is likely to be important in the pathogenesis of hepatic diseases.