Submitted on November 13, 2007
Accepted on March 6, 2008
Differential Mechanisms of Hepatic Vascular Dysregulation with Mild vs Moderate Ischemia / Reperfusion
Sang Ho Lee1, Cathy Culberson1, Katarzyna Korneszczuk1, and Mark G Clemens1*
1 Biology, UNC Charlotte, Charlotte, North Carolina, United States
* To whom correspondence should be addressed. E-mail: mgclemen{at}uncc.edu.
Endotoxemia produces hepatic vascular dysregulation resulting from inhibition of endothelin (ET)-stimulated NO production. Mechanisms include overexpression of caveolin-1 (Cav-1) and altered phosphorylation of eNOS in sinusoidal endothelial cells. Since ischemia / reperfusion (I/R) also causes vascular dysregulation, we tested whether the mechanisms are the same. Rats were exposed to either mild (30 min) or moderate (60 min) hepatic ischemia in vivo followed by reperfusion (6 h). Livers were harvested and prepared into precision cut liver slices (PCLS) for in vitro analysis of NOS activity and regulation. Both I/R injuries significantly abrogated both the ET-1 (1µM) and the ETB receptor agonist (IRL-1620, 0.5µM)-mediated stimulation of NOS activity. 30 min I/R resulted in over-expression of Cav-1 and loss of ET-stimulated phosphorylation of Ser1177 on eNOS, consistent with an inflammatory response. 60 min I/R also resulted in loss of ET-stimulated Ser1177 phosphorylation, but Cav1 expression was not altered. Moreover, expression of ETB receptors was significantly decreased. This suggests that the failure of ET to activate eNOS following 60 min I/R is associated with decreased protein expression consistent with ischemic injury. Thus, hepatic vascular dysregulation following I/R is mediated by inflammatory mechanisms with mild I/R while ischemic mechanisms dominate following more severe I/R stress.
