Effects of epinephrine on underperfusion-reperfusion injuries in diabetic and non-diabetic rat hearts

The sympathetic nervous systems may bear relevance to the increased incidence of heart failure in diabetes (DM). In our isolated rat hearts perfused at constant low flow rate, norepinephrine dose-dependently enhanced diabetic myocardial damage, particularly during underperfusion. The purpose of this investigation is to examine the effects of epinephrine on the ischemic injury and on the reperfusion injury in DM and non-DM rat hearts, and to clarify whether the cardiac states during underperfusion at constant low pressure are similar to those at constant low flow rate. Isolated streptozotocin-induced 6-week DM and non-DM rat hearts with a balloon in the left ventricle (LV) were paced and normal perfused at 75 cm H2O with normoxic Krebs-Henseleit solution. Then the hearts were underperfused at 35 cm H2O, a constant low pressure with below one-third of the pre-ischemic coronary perfusion flow (CPF) level. Four min after the start of underperfusion, the perfusate was changed to that containing epinephrine 10(-6) M. After 45 min underperfusion with or without epinephrine, all of the hearts were reperfused without epinephrine at 75 cm H2O for 45 min. To detect changes in LV stiffness, the isometric tension along the longitudinal direction of the whole heart and the LV isovolumic pressure were monitored simultaneously. In DM hearts, the underperfusion alone caused a slight increase in LV stiffness, and all the changes recovered to the pre-ischemic levels during reperfusion. Epinephrine during underperfusion accelerated the start of increase in LV stiffness and the decrease in CPF. During reperfusion the changes recovered partly to the control levels. In non-DM hearts, epinephrine during underperfusion caused only a slight increase in LV stiffness though a similar low CPF to DM hearts. However, the reperfusion caused a marked increase in LV stiffness and a lower recovery of CPF. Epinephrine at constant low pressure, as well as norepinephrine at constant low flow rate, enhanced the ischemic injury, particularly in DM hearts, while aggravated the reperfusion injury in non-DM hearts.