MONOPHOSPHORYL LIPID-A PRESERVES MYOCARDIAL CONTRACTILE FUNCTION FOLLOWING MULTIPLE, BRIEF PERIODS OF CORONARY-OCCLUSION IN DOGS

The effects of a 1- or 24-hour pretreatment regimen with monophosphory l lipid A (MLA, 35 mu g/kg i.v.) on myocardial stunning produced by re petitive coronary occlusions were studied in barbital-anesthetized dog s. Regional segment function (% SS) and myocardial blood flow were mea sured by sonomicrometry and the radioactive microsphere technique, res pectively. In controls, six 5-min periods of coronary occlusion interp ersed with IO-min periods of reperfusion and ultimately followed by 2 h of reperfusion produced regional segment dysfunction. Pretreatment w ith MLA for Ih prior to the first occlusion period had no effect on % SS, however, pretreatment with MLA 24 h prior to the first occlusion p eriod 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 sign ificantly less severe in animals receiving a 24-hour pretreatment with MLA as compared to the controls, These results are the first to demon strate that MLA, a lipid A derivative of endotoxin, preserves contract ile function of ischemic myocardium in an in vivo canine model and tha t its cardio-protection is time dependent.