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 r ole in the regulation of coronary flow and cardiac function and structure i n normal and pathological conditions such as ischemia-reperfusion (I/R) inj ury. The aim of this study was to investigate the effects of the Angiotensi n II type 1 (AT-1) receptor antagonist MK-954 (losartan potassium) on posti schemic endothelial dysfunction and NOS mRNA expression (inducible nitric o xide synthase, iNOS; endothelial nitric oxide synthase, eNOS) in isolated w orking rat hearts. Methods: isolated working rat hearts were subjected to 1 5 min global ischemia and 180 min reperfusion. MK-954 was added to perfusio n buffer (a modified Krebs-Henseleit solution) at 1 muM concentration. We a ssessed functional parameters, creatin kinase (CK) release, heart weight ch anges, microvascular postischemic hyperpermeability (FITC-albumin extravasa tion) and morphological ultrastructural alterations. eNOS and iNOS mRNA lev els were also detected by the means of multiplex RT-PCR technique using gly ceraldehyde-3-phosphate dehydrogenase (G3PDH) gene as internal control; res ults were expressed as densitometric ratio. Results: in Losartan-treated he arts we observed a significant reduction of postischemic contractile dysfun ction, CK release and myocardial ultrastructural damage; postischemic FITC- albumin extravasation was significantly reduced respect to controls. Moreov er, 1 muM Losartan produced a significant reduction of eNOS/G3PDH respect t o untreated hearts submitted to I/R. Regarding iNOS/G3PDH ratio, no signifi cant changes were detected in Losartan-treated hearts compared with control s. Conclusions: our study revealed that Losartan treatment before ischemia, and during reperfusion, is able to reduce the reperfusion injury of the ra t heart by reducing mechanical and microcirculatory dysfunction and necroti c cell death, ameliorating cardiac ultrastructure and endothelial protectio n, probably inducing eNOS over-expression and reducing post-ischemic hyperp ermeability of coronary microcirculation. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.