Role of Endothelin-1 and Cyclic Nucleotides in Ischemia/Reperfusion-Mediated Microvascular Leak

BACKGROUND:A consequence of ischemia/reperfusion (IR) is endothelial barrier dysfunction and intravascular volume loss. The purposes of our study are to explore the impact of1) cyclic guanosine monophosphate (cGMP) synthesis inhibition, 2) cyclic adenosine monophosphate (cAMP) synthesis inhibition, 3) treatment with endothelin-1, and 4) endothelin-1 (ET-1)-mediated cAMP changes on IR-induced fluid leak. We hypothesize that IR-mediated microvascular fluid leak results from increased cGMP activity and ET-1 decreases IR-induced fluid leak via cAMP. METHODS:A micro-cannulation technique was used to determine fluid leak or hydraulic permeability (Lp) in rat mesenteric venules. Lp was measured during IR and after treatment with 1) cGMP synthesis inhibitor (LY83583,10 μmol/L) 2) cAMP synthesis inhibitor (2′,5′dideoxyadenosine,10 μmol/L), 3) ET-1 (80 pM), and 4) cAMP synthesis inhibitor plus ET-1 (n = 6 in each group; Lp represented as mean ± standard error of the mean; units 10-cm/sec/cmH2O). RESULTS:IR resulted in an increase in Lp (Lp = 7.07 ± 0.20) sevenfold above baseline (1.05 ± 0.31) (p ≤ 0.001). Compared with IR alone, 1) pretreatment with cGMP synthesis inhibitor completely blocked IR-induced fluid leak (Lp = 1.08 ± 0.18) (p ≤ 0.001), 2) pretreatment with cAMP synthesis inhibitor attenuated fluid leak (Lp = 3.92 ± 0.20) (p ≤ 0.005), 3) treatment with ET-1 decreased fluid leak (Lp = 5.38 ± 0.28) (p ≤ 0.005), and 4) pretreatment with a cAMP inhibitor plus treatment with ET-1 reduced fluid leak nearly 50% compared with ET-1 alone (Lp = 2.95 ± 0.12) (p ≤ 0.005). CONCLUSION:cGMP inhibition completely blocks fluid leak, pointing toward a central role as a mediator of IR-induced postcapillary venular leak. ET-1 mildly decreased leak. Furthermore, ET-1 may not exert its effects on microvascular fluid leak during IR via cAMP.