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 of: 1) 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 (L_p) in rat mesenteric venules. L _p 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; L_p represented as mean ± standard error of the mean; units 10-⁷cm/sec/cmH ₂O). Results: IR resulted in an increase in L_p (L _p = 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 (L_p = 1.08 ± 0.18) (p ≤ 0.001), 2) pretreatment with cAMP synthesis inhibitor attenuated fluid leak (L_p = 3.92 ± 0.20) (p ≤ 0.005), 3) treatment with ET-1 decreased fluid leak (L_p = 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 (L_p = 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.