Altered endothelin receptor subtype expression in hepatic injury after ischemia/reperfusion.

This study was performed to determine whether ischemia/reperfusion (I/R) injury in rat liver results in alterations in endothelin receptor expression. Hepatic ischemia was produced in rats for 60 min followed by 6 or 24 h reperfusion. Portal inflow pressure was increased (7.38+/-0.60 mmHg) at 24 hours after reperfusion. Serum ALT increased significantly at both 6 and 24 h (6 h; 258.3+/-74.3, 24 h; 243.1+/-74.8 IU/L). Portal vascular response to an endothelin-B receptor agonist (IRL 1620) was significantly increased in the I/R livers compared to control and this was potentiated by L-NAME. IRL 1620 also caused LDH release from I/R livers but not controls. LDH release after IRL 1620 in I/R livers correlated with increased portal pressure response. To determine whether the altered response might be the result of altered endothelin receptor expression, livers were harvested after reperfusion and total endothelin binding sites were determined by competitive binding with ET-1. Proportion of endothelin receptor subtypes (ET(A)/ET(B)) was determined using the ET(A) antagonist BQ-610 (1 microM) and ET(B) agonist IRL-1620 (100 nM). There were no significant changes in Kd but Bmax for endothelin-1 was decreased in I/R group especially non-ischemic lobe at 24 h. ET(A) receptors were significantly decreased whereas ET(B) receptors were increased. These changes were more pronounced at 24 h after reperfusion than at 6 h. Interestingly, the changes in ET receptors was observed identically both in ischemic and non-ischemic lobes (ischemic lobe ET(A) 41.9%, ET(B) 51%; non-ischemic lobe ET(A) 38.8%, ET(B) 49.5%). These results indicate that the major functional endothelin receptor subtype upregulated in I/R is the ET(B) receptor and that this upregulation may contribute to microvascular dysregulation and hepatic injury.