Effects of κ-opioid agonist U50,488H postconditioning on early cardiac function in rats undergoing cardiac resuscitation

Objective To investigate the effects of κ-opioid agonist U50,488H postconditioning on early cardiac function and success rate of resuscitation in rats undergoing cardiac arrest. Methods The SD rats with cardiac arrest were subjected to three different interventional resuscitation: operation with saline treatment (group Con), with epinephrine treatment (group Epi), with combinatory treatment of epinephrine and U50,488H(group EU). Each group eventually had 20 survivors after 2 h recovery. Before cardiac resuscitation, both Con and Epi groups were administrated with 0.2 ml of normal saline and group EU was administrated with 0.2 ml of U50,488H (1 mg/kg) through femoral vein. During cardiac resuscitation, both Epi and EU groups were administrated with epinephrine. Hemodynamic and cardiac function parameters were obtained at 0 min, 10 min, 30 min, 1 h, 2 h after spontaneous circulation recovery. And the success rate of resuscitation among three groups were calculated. Results The survival rate at 30 min and 2 h after cardiac resuscitation did not differ between group Epi and group EU(P>0.05). Compared with group Con, the time of spontaneous circulation recovery (Tcpr) was significantly decreased in both group Epi and group EU (P<0.05). Compared with those in group Epi, there was no difference in all parameters of cardiac function, including HR, MAP, maximal rising rate of blood pressure in the ventricular chamber (dp/dtmax), maximal decline rate of blood pressure in the ventricular chamber(-dp/dtmax) and left ventricular end-diastolic pressure (LVEDP) in group EU at immediately, 10 min, 30 min and 1 h after resuscitation. At 2 h after resuscitation, MAP, dp/dtmax, -dp/dtmax, and LVEDP were significantly different in group EU, compared with those in group Epi(P<0.05). Conclusions These results demonstrate that a combination of epinephrine and κ-opioid agonist U50,488H(1 mg/kg) did not affect the success rate of early resuscitation in rats undergoing cardiac arrest, but improves left ventricular systolic and diastolic functions 2 h after resuscitation, compared with epinephrine treatment alone. Key words: Cardiac arrest; Ischemia-reperfusion injury; Resuscitation; κ-opioid receptor; Postconditioning