| Cardioprotection induced by ischemic preconditioning is a biphasic event. The acute or early phase occurs immediately after the ischemic preconditioning stimulus and lasts for 1 to 3 hours while the delayed or late phase is seen 12 to 24 hours after the initial stimulus and lasts up to 72 hours. Opioids have been shown to confer both the early and late phase of cardioprotection similar to ischemic preconditioning. As one of the most widely used opioids for the treatment of pain, morphine has been shown to induce the early phase cardioprotection. In contrast, no work has been conducted concerning the delayed cardioprotection induced by morphine.There is mounting evidence suggesting that iNOS is an essential trigger and/or mediator of the late phase of myocardial preconditioning induced by ischemia preconditioning or by a number of pharmacological agents. eNOS may contribute to the early, as well as the late cardioprotection. However, nothing is known about the effects of NOS in morphine - induced cardioprotection. Although no work has been performed concerning the role of morphine on NO activities in myocardium, it has been demonstrated that morphine facilitates NO release in human monocytes, neutrophils, and endothelial cells and stimulates iNOS expression in macrophages.The present study sought to examine the possibility of morphine - induced delayed cardioprotection in a murine model of coronary artery occlusion and reperfusion injury and to determine the potential involvement of iNOS in this protection using a pharmacological inhibitor and gene - knockout mice.Materials and MethodsAnimals: Adult male iNOS gene - knockout ( -/- ) B6, 129 mice were purchased from the Jackson Laboratory (Bar Harbor, ME). Wild type (WT) mice ( Jackson Laboratory) with a genetic background as close as possible to the iNOS gene - knockout mice ( B6129PF2/J) were used as controls.Surgical Procedures: Animals were anesthetized with pentobarbital sodium. A tracheotomy was performed and the animals were mechanically ventilated u-sing a rodent ventilator. The right carotid artery was cannulated with Polyethylene -10 tubing to monitor hemodynamics. Core temperature was measured and maintained at 36.5 - 37. 51C. Iigation of the left anterior descending coronary artery was performed using a 7 - 0 silk suture with a small piece of polyethylene tubing to secure the ligature without damaging the artery. Ischemia was confirmed by visual inspection of blanching in the myocardium distal to the site of occlusion. After a period of coronary occlusion of 45 minutes, the 7-0 silk ligature was removed. Reperfusion was confirmed visually by the return of a red color in the region that was previously pale.Experimental Protocols: Mice were pretreated with morphine or saline 24 hours before a 45 - minute period of coronary occlusion followed by 120 minutes of reperfusion. Seven groups were enrolled. WT mice were randomly divided into the following five groups. (1) Saline: pretreated with saline (0. lml, IP) ; (2) MO. 1: pretreated with morphine (0.1mg/kg, IP) ; (3) M0.3: pretreated with morphine (0.3mg/kg, IP) ; (4) Saline +SMT: pretreated with saline (0. lml, IP) and SMT (3mg/kg, IP) which was administered 30 minutes before coronary occlusion; (5) M0. 3 +SMT: pretreated with morphine (0. 3mg/kg, IP) and SMT (3mg/kg, IP) which was administered 30 minutes before coronary occlusion. iNOS gene - knockout mice were assigned randomly to another two groups. (6) iNOS - KO + saline: pretreated with saline (0. lml, IP) ; (7) iNOS - KO + M0.3: pretreated with morphine (0.3mg/kg, IP).Determination of Risk and Infarct Sizes: At the end of the 120 - minute reperfusion period, the left anterior descending coronary artery was occluded a-gain and Evans blue was infused into the carotid artery catheter in a retrograde manner. The heart was cut into five transverse slices and was incubated in 1% TTC for 5 minutes at 37C. After fixation, each slice was weighed and photographed. The left ventricular area, AAR ( absence of blue dye) , and area o...
|
PDF Full Text Request