beta-Adrenoceptor blocking activities of nipradilol and its optical isomers in pig coronary artery

Effects of landiolol on mechanical and metabolic changes in rat reperfused ischaemic hearts

1. The aim of the present study was to clarify the effects of landiolol, a short-acting selective beta(1)-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 micromol/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/dt(max)) 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/dt(max), decreased myocardial ATP content and increased Pi and LDH release. In the 30 micromol/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 micromol/L landiolol-treated group, cardiac contractile dysfunction was improved and myocardial MDA, ATP and Pi contents were preserved. All measurements in the 100 micromol/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 micromol/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.

Vasoconstriction of porcine left anterior descending coronary artery by ecstasy and cathinone is not an indirect sympathomimetic effect

3,4-methylenedioxymethamphetamine ('Ecstasy', MDMA) and cathinone, the active constituent of khat leaves, were examined on pig isolated left anterior descending coronary arteries to determine whether they cause vasoconstriction and whether this was an indirect sympathomimetic action. Coronary artery rings were set up in Krebs solution (37 degrees C) gassed with 5% CO2 in O2. Endothelium remained intact as indicated by relaxation by bradykinin. Isometric tension was recorded and cumulative concentration-response curves (CRCs) for noradrenaline, ecstasy or cathinone plotted as a percent of the constriction to KCl (60 mM). Noradrenaline-induced contractions of the coronary artery were enhanced by propranolol (1 microM) indicating beta-adrenoceptor-mediated opposing vasodilatation. Cocaine (10 microM) further potentiated, while prazosin (1 microM) virtually abolished the contractions to noradrenaline. Cathinone and ecstasy constricted the coronary artery rings, the peak contractions being 56.5+/-4.2% (n=4) and 37.3+/-2.4% (n=4), respectively. Higher concentrations relaxed. The vasoconstriction was not affected by cocaine (10 microM), prazosin (1 microM, in the presence of cocaine) or removal of the endothelium. There was no tachyphylaxis or desensitisation on repeated administration of single doses. Ecstasy- and cathinone-induced coronary vasoconstriction is therefore via mechanisms other than indirect sympathomimetic activity or alpha1 -adrenoceptors. This activity could explain the cardiac adverse effects following their excessive use.