lipid-a and Arterial-Occlusive-Diseases

Bacterial endotoxin reduces the severity of ventricular arrhythmias which occur when a coronary artery is occluded several hours later. We have now examined in anaesthetised dogs the effects on ischaemia and reperfusion-induced arrhythmias, of a non-toxic derivative component of the endotoxin molecule of the lipid-A (monophosphoryl lipid-A). This was given intravenously, in doses of 10 and 100 microg kg(-1), 24 h prior to coronary artery occlusion. Arrhythmia severity was markedly reduced by monophosphoryl lipid-A. During ischaemia, ventricular premature beats were reduced from 315+/-84 in the vehicle controls to 89+/-60 (with the lower dose of monophosphoryl lipid-A) and 53+/-23 (P<0.05) with the higher dose. The incidence of ventricular tachycardia was reduced from 75% to 25% (P<0.05) and 31% (P<0.05), and the number of episodes of ventricular tachycardia from 13.4+/-4.9 per dog to 1.1+/-1.1 (P<0.05) and 1. 2+/-0.9 (P<0.05) after doses of 10 and 100 microg kg(-1), respectively. The incidence of ventricular fibrillation during occlusion and reperfusion in the control group was 96% (15/16), i.e., only 6% (1/16) dogs survived the combined ischaemia-reperfusion insult. Monophosphoryl lipid-A (100 microg kg(-1)) significantly reduced the incidence of occlusion-induced ventricular fibrillation (from 50% to 7%; P<0.05), and increased survival following reperfusion to 54% (P<0.05). Monophosphoryl lipid-A also significantly reduced ischaemia severity as assessed from ST-segment elevation recorded from epicardial electrodes as well as the degree of inhomogeneity of electrical activation within the ischaemia area. There were no haemodynamic differences prior to coronary occlusion between vehicle controls and monophosphoryl lipid-A-treated dogs. These results demonstrate that monophosphoryl lipid-A reduces arrhythmia severity 24 h after administration. Although the precise mechanisms are still unclear, there is some evidence that nitric oxide and prostanoids (most likely prostacyclin) may be involved because the dual inhibition of nitric oxide synthase and cyclooxygenase enzymes by administration of aminoguanidine and meclofenamate abolished the marked antiarrhythmic protection resulted from monophosphoryl lipid-A treatment 24 h previously.

Topics: Animals; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; Arterial Occlusive Diseases; Coronary Vessels; Disease Models, Animal; Dogs; Enzyme Inhibitors; Female; Guanidines; Heart Ventricles; Hemodynamics; Lipid A; Male; Meclofenamic Acid; Myocardial Ischemia; Myocardial Reperfusion Injury; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Prostaglandin-Endoperoxide Synthases; Severity of Illness Index; Tachycardia, Ventricular; Time Factors; Ventricular Fibrillation

The effects of a 1- or 24-hour pretreatment regimen with monophosphoryl lipid A (MLA, 35 micrograms/kg i.v.) on myocardial stunning produced by repetitive coronary occlusions were studied in barbital-anesthetized dogs. Regional segment function (%SS) and myocardial blood flow were measured by sonomicrometry and the radioactive microsphere technique, respectively. In controls, six 5-min periods of coronary occlusion interpersed with 10-min periods of reperfusion and ultimately followed by 2 h of reperfusion produced regional segment dysfunction. Pretreatment with MLA for 1 h prior to the first occlusion period had no effect on %SS, however, pretreatment with MLA 24 h prior to the first occlusion period resulted in a significant (p < 0.05) improvement in the recovery of %SS at all reperfusion periods as compared to the control group. In addition, segment dysfunction during each occlusion period was significantly less severe in animals receiving a 24-hour pretreatment with MLA as compared to the controls. These results are the first to demonstrate that MLA, a lipid A derivative of endotoxin, preserves contractile function of ischemic myocardium in an in vivo canine model and that its cardio-protection is time dependent.

Topics: Animals; Arterial Occlusive Diseases; Blood Gas Analysis; Body Weight; Coronary Circulation; Coronary Disease; Dogs; Female; Hemodynamics; Hydrogen-Ion Concentration; Hypertrophy, Left Ventricular; Lipid A; Male; Microspheres; Myocardial Contraction; Myocardial Reperfusion Injury; Organ Size