Inability of the Heat-shocked Heart to Adjust its Pre-ischemic and Post-ischemic Performance to Variable Loading Conditions

The aim of the present study was to investigate whether the pre-ischemic and post-ischemic hemodynamic function of the heat-shocked rat heart is affected by changes in afterload and extracellular calcium concentrations ( [Ca2 +]e). Experiments were performed on isolated, ejecting Lewis rat hearts 24 h afterin vivoheat shock (LewHS) or anesthesia alone (LewC).In vitrohearts were subjected to 60 min normoxic perfusion, 45 min global ischemia, and 60 min of reperfusion. Pre-ischemic and post-ischemic left ventricular performance was evaluated at [Ca2 +]eranging between 0.65 and 3.0 m at afterloads of 8.0 kPa and 16.0 kPa. At 8.0 kPa, pre-ischemic function was comparable in LewHSand LewCat [Ca2 +]eequal to or above 2.25 m . At lower [Ca2 +]e, i.e., 0.65 and 1.25 m , cardiac output (CO) was significantly lower in LewHSthan in LewChearts. At 16.0 kPa, significantly lower CO values were found in LewHSthan LewChearts at all [Ca2 +]elevels. During post-ischemic reperfusion under basal conditions (8.0 kPa; [Ca2 +]e=2.25 m ) a significantly better recovery was observed in LewHSthan LewChearts, persisting at [Ca2 +]eequal to 1.25 m . However, either by lowering [Ca2 +]eto 0.65 m or increasing afterload to 16.0 kPa (at all [Ca2 +]e), heat shock-associated improvement of post-ischemic performance disappeared. In conclusion, pre-ischemic left ventricular performance of the isolated heat-shocked heart is depressed when it performs at low [Ca2 +]eor against a relatively high afterload. The heat shock-mediated improvement of post-ischemic function is only present at relatively low afterload levels in combination with normal extracellular calcium concentrations.