Cardiac tissue iron: Effects on post-ischemic function and free radical production, and its possible role during preconditioning

We determined whether prior treatment of rats (study 1) with subthreshold d oses of iron (no evidence of cardiac tissue overload), or in vitro ischemic pre-conditioning (IP: 5 min. Ischemia (I)/5 min. Reperfusion (R)x 2 cycles ) of hearts from untreated rats (study 2), can modulate redox-active cardia c tissue iron levels or distribution, leading to alterations in post-ischem ic lipid peroxidation-derived free radical (FR) production and severity of reperfusion injury. In study 1, rats received biweekly i.p. injections of 0 (saline=S), 3, 6, or 12 mg FeCl3/ml for 3-wks prior to imposing 30 min. I / 15 min. R in vitro. The highest dose caused no elevations in plasma or he art tissue Fe levels, but did further reduce post-ischemic recoveries of le ft ventricular developed pressure (17% lower), cardiac work (57%) and outpu t (54%), and increased effluent lipid hydroperoxides (2.1-fold) compared to the S-group. Postischemic FR production was assessed in toluene-extracted effluent by ESR spectroscopy and alpha -phenyl-N-tert butylnitrone (PBN=2.5 mM perfusate) spin trapping. PBN/alkoxyl (alpha (H)=1.90 G, alpha (N)=13.6 3 G) was the dominant signal detected in all groups; however, Fe-treated gr oups displayed significant dose-dependent increases in total alkoxyl conten t (3, 6, 12 mg/ml:1.8-, 2.3-, 2.7-fold higher) compared to the S-group. The se data suggest that even mild, non-overloading doses of iron can be functi onally and oxidatively detrimental to hearts when an YR stress is imposed. In study 2, isolated hearts from untreated rats were exposed to two - IP cy cles: during IF, total effluent iron content (atomic absorption) increased 11.4-fold compared to control and analysis of cardiovascular tissue iron di stribution (X-ray microanalysis) suggested that iron loss from capillary en dothelium was far greater than from tissue myocytes, Moreover, iron-catalyz ed production of alkoxyl radicals following severe I/R stress (40 min. I/15 min. R) was substantially lower (73%) in IP hearts compared to the non-IF counterparts. These preliminary findings suggest that cardioprotection resu lting from IP may, in part, be related to IF-induced release of cardiovascu lar endothelial iron (redox-active) prior to imposing severe I/R stress.