MK-954 (losartan potassium) exerts endothelial protective effects against reperfusion injury: evidence of an e-NOS mRNA overexpression after global ischemia.

Background: the cardiac Renin-Angiotensin system (RAS) plays an important role in the regulation of coronary flow and cardiac function and structure in normal and pathological conditions such as ischemia-reperfusion (I/R) injury. The aim of this study was to investigate the effects of the Angiotensin II type 1 (AT-1) receptor antagonist MK-954 (losartan potassium) on postischemic endothelial dysfunction and NOS mRNA expression (inducible nitric oxide synthase, iNOS; endothelial nitric oxide synthase, eNOS) in isolated working rat hearts.

Methods: isolated working rat hearts were subjected to 15 min global ischemia and 180 min reperfusion. MK-954 was added to perfusion buffer (a modified Krebs-Henseleit solution) at 1 microM concentration. We assessed functional parameters, creatin kinase (CK) release, heart weight changes, microvascular postischemic hyperpermeability (FITC-albumin extravasation) and morphological ultrastructural alterations. eNOS and iNOS mRNA levels were also detected by the means of multiplex RT-PCR technique using glyceraldehyde-3-phosphate dehydrogenase (G3PDH) gene as internal control; results were expressed as densitometric ratio.

Results: in Losartan-treated hearts we observed a significant reduction of postischemic contractile dysfunction, CK release and myocardial ultrastructural damage; postischemic FITC-albumin extravasation was significantly reduced respect to controls. Moreover, 1 microM Losartan produced a significant reduction of eNOS/G3PDH respect to untreated hearts submitted to I/R. Regarding iNOS/G3PDH ratio, no significant changes were detected in Losartan-treated hearts compared with controls.

Conclusions: our study revealed that Losartan treatment before ischemia, and during reperfusion, is able to reduce the reperfusion injury of the rat heart by reducing mechanical and microcirculatory dysfunction and necrotic cell death, ameliorating cardiac ultrastructure and endothelial protection, probably inducing eNOS over-expression and reducing post-ischemic hyperpermeability of coronary microcirculation.