EFFECTS OF LANDIOLOL ON MECHANICAL AND METABOLIC CHANGES IN RAT REPERFUSED ISCHAEMIC HEARTS

SUMMARY 1 The aim of the present study was to clarify the effects of landiolol, a short‐acting selective β1‐adrenoceptor blocking agent, on mechanical and metabolic changes in postischaemic perfused hearts. 2 Rat isolated hearts (n = 30) were randomly separated into non‐ischaemic or ischaemic groups. The latter group was further divided into Krebs’–Henseleit solution (KHS)‐ and landiolol (30, 100 or 300 µmol/L)‐treated groups. Ischaemic hearts were subjected to 25 min global ischaemia and 20 min reperfusion under atrial pacing. Time‐course changes in left ventricular (LV) end‐diastolic pressure (LVEDP), LV developed pressure (LVDP), peak positive velocity of change of LV pressure (LVdP/dtmax) and coronary flow were observed along with tissue contents of adenosine triphosphate (ATP), creatine phosphate, inorganic phosphate (Pi), malondialdehyde (MDA) and lactate dehydrogenase (LDH) release in coronary effluent. The effects of landiolol on rat isolated aortic preparations under KCl contraction were also investigated. 3 Ischaemia–reperfusion significantly impaired cardiodynamics, such as LVEDP, LVDP and LVdP/dtmax, decreased myocardial ATP content and increased Pi and LDH release. In the 30 µmol/L landiolol‐treated group, cardiovascular parameters impaired by ischaemia–reperfusion and increased LDH release were further exacerbated and myocardial MDA content was significantly increased. In the 300 µmol/L landiolol‐treated group, cardiac contractile dysfunction was improved and myocardial MDA, ATP and Pi contents were preserved. All measurements in the 100 µmol/L landiolol‐treated group were similar to those in the ischaemic KHS group. Furthermore, significant relaxations of isolated aortic preparations were obtained with landiolol 30–1000 µmol/L, suggesting a possible calcium antagonism with landiolol. 4 In conclusion, landiolol, at low concentrations, aggravated myocardial ischaemia–reperfusion injuries, whereas at high concentrations it ameliorated them. The former effect may be mediated by the production of reactive oxygen species, whereas the latter may involve calcium antagonist activity.