The different concentrations we chose RG7420 chemical structure to test were derived from previous publications on the subject. In in vitro studies, the average concentration of CsA leading to observable positive effects in cellular bath solution is 1 μM [15, 20, 30]. Higher concentrations (10 and 30 μM) were chosen from previous in vivo publications reporting blood concentrations of CsA between 1 and 5 μM in humans [8, 47], and up to 90 μM in rats [26].

In our data, CsA has shown to be deleterious on pressures and resistances, with a dose-dependent effect. Although daily administrations of CsA for three weeks seemed to prevent pulmonary hypertension induced by chronic hypoxia [24], several studies showed that CsA could be responsible for hypertension in humans after lung, heart, kidney, or liver transplantations [16, 29, 38, 49]. Two stages were described, the first,

which was acute hypertension during initiation of CsA treatment, BI 2536 order and second, a chronic hypertension after long-term administration. CsA binds to Cyclophilin-A (an immunophilins cytoplasmic receptor) in smooth vascular muscles and may directly affect blood pressure regulation by reducing the endothelial production of nitric oxide by NO synthase [37]. This mechanism could account for the increase in PAP, Pcap, and PVR we observed in our lungs treated with CsA, especially those receiving higher doses (10 and 30 μM). It has been studied that IRI induces a hypoxic mediator-induced active vasoconstriction, which results in a perivascular compression by edema, and an intravascular obstruction by thromboembolism or endothelial swelling [13]. The active reversible vasoconstriction accounts for approximately fifty percent of the hypoxic pulmonary hypertension. Endothelial cell exposure to CsA generates reactive oxygen and nitrogen species [35] that may

enhance this pulmonary vasoconstriction. These early hemodynamic effects may be synergic with intrinsic cellular properties Megestrol Acetate of CsA against IRI. However, beyond a certain level of CsA (over 10 μM in our experiment), vasoconstriction and blood flow redistribution may aggravate the injury by an over-perfusion of mildly injured zones. Increasing blood flow and PAP to lesser damaged and equally injured zones can allow for major fluid filtration through the capillary-alveolar membrane as described by the Starling equation [42]. Over-perfusion could have re-opened non-flowing leaky capillaries in zone 1, called “blind capillaries” (i.e., open at their arterial end and obstructed at their venous end) and shifted the obstruction point downstream under zone 2 conditions toward the venous ends of the capillaries and veinules. These microvascular mechanisms have been described in other models of isolated lung injury [2, 6], which were consistent with an increase of the post-capillary (i.e., veinular) part of the PVR observed in our experiments with high doses of CsA.