The benefits of acute d-propranolol (d-Pro, non–β-adrenergic receptor blocker) pretreatment against enhanced ischemia/reperfusion (I/R) injury of hearts from moderate iron-overloaded rats were examined. Perfused hearts from iron-dextran-treated rats (450 mg/kg/week for 3 weeks, intraperitoneal administration) exhibited normal control function, despite iron treatment that elevated plasma iron and conjugated diene levels by 8.1-and 2.5-fold, respectively. However, these hearts were more susceptible to 25 mins of global I/R stress compared with nonloaded hearts; the coronary flow rate, aortic output, cardiac work, left ventricular systolic pressure, positive differential left ventricular pressure (dP/dt), and left ventricular developed pressure displayed 38%, 60%, 55%, 13%, 41%, and 15% lower recoveries, respectively, and a 6.5-fold increase in left ventricular end-diastolic pressure. Postischemic hearts from iron-loaded rats also exhibited 5.6-, 3.48-, 2.43-, and 3.45-fold increases in total effluent iron content, conjugated diene levels, lactate dehydrogenase (LDH) activity, and lysosomal N-acetyl-β-glucosaminidase (NAGA) activity, respectively, compared with similarly stressed nonloaded hearts. A comparison of detection time profiles during reperfusion suggests that most of the oxidative injury (conjugated diene) in hearts from iron-loaded rats occurred at later times of reperfusion (8.5-15 mins), and this corresponded with heightened tissue iron and NAGA release, d-Pro (2 μM infused for 30 mins) pretreatment before ischemia protected all parameters compared with the untreated iron-loaded group; pressure indices improved 1.2- to 1.6-fold, flow parameters improved 1.70- to 2.96-fold, cardiac work improved 2.87-fold, and end-diastolic pressure was reduced 56%. d-Pro lowered total release of tissue iron, conjugated diene content, LDH activity, and NAGA activity 4.59-, 2.55-, 3.04-, and 4.14-fold, respectively, in the effluent of l/R hearts from the iron-loaded group. These findings suggest that the enhanced postischemic dysfunction and tissue injury of hearts from iron-loaded rats was caused by excessive iron-catalyzed free radical stress, and that the membrane antioxidant properties of d-Pro and its stabilization of sequestered lysosomal iron by d-Pro may contribute to the cardioprotective actions of d-Pro.

Indices of reperfusion (R) injury in global ischemic (I) hearts from iron-dextran (Fe-D) overloaded rats were examined with or without acute d-propranolol (d-Pro, non-beta adrenergic receptor blocker) pretreatment. Prior to I, isolated working hearts from Fe-D treated rats (450 mg/kg/wk × 3 wks, i.p.) were perfused (control) 45 min with physiologic Krebs-Henseleit buffer (95% O2:5% CO2;1.25 mM CaCl2;10.0 mM glucose); baseline cardiac work (CW) and biochemical (effluent Fe, conjugated diene [CD] content, lactate dehydrogenase [LDH] and lysosomal N-acetyl-beta-glucosaminidase [NAGA] activities) measurements were taken. In parallel studies, 2 μM d-Pro was infused (0.5 ml/min) during the last 30 min of control perfusion. All hearts received 25 min I/30 min R, and measurements were repeated. Fe-D-loaded hearts were more susceptible to I/R vs non-loaded: cardiac work recovery was 55% lower, and they exhibited several fold increases in total effluent Fe (5.6×), CD (3.48×), LDH (2.43×), and NAGA (3.45×) vs non-loaded. Detection time-courses showed early disruption of plasmalemmal integrity (LDH maximum at 3 min R), but much of the oxidative injury in Fe-D hearts occurred later in R (8.5–15 min), and corresponded with heightened Fe and NAGA release. Linear regression analyses of time-course values for Fe-D hearts demonstrated positive temporal correlations for: CD vs NAGA (r = 0.85); Fe vs CD (r = 0.76); Fe vs NAGA (r = 0.79); but not Fe vs LDH. D-Pro protected all measured parameters: CW improved 2.87-fold; tissue release of Fe (4.59×), CD (2.55×), LDH (3.04×) and NAGA (4.14×) were decreased; and temporal correlations were abolished, except for CD vs NAGA, which remained linear (r = 0.84) even at attenuated levels. These findings suggest that enhanced I/R oxidative tissue injury of Fe-D hearts was temporally-associated with excessive lysosomal Fe-release and related free radical stress, and d-Pro's membrane antioxidant properties and stabilization of sequestered lysosomal Fe contributed to its cardioprotective actions.

Cardioprotection by Mg Sulfate (MgSO4) during ischemia/reperfusion (I/R) is attributed largely to the Mg2+ cation. However, Mg-gluconate (MgGl2) may provide added benefit, possibly through its anion's antioxidant properties. Protective effects of both Mg-salts and their anions during 30 min global I and 50 min R were assessed in Langendorff-perfused (Krebs-Henseleit buffer) rat hearts. Recovery of function was compared between untreated hearts and those receiving supplement (2.4 mM MgGl2, MgSO4, or Na2SO4, or 4.8 mM NaGl) for 5 min prior to I and during the initial 30 min R. The final 20 min R was conducted without supplement. End diastolic pressure (EDP, mmHg) of the 50 min reperfused MgGl2 group (2.6) was lower than MgSO4 (16.2) and untreated (35.6) groups, and the NaGl group (25.2) was considerably lower than Na2SO4 (38.8). Recovery of developed pressure (% preischemic DP) at the onset of R for MgGl2 (74.9) was greater than MgSO4 (37.9) and untreated (33.2). After 50 min, MgGl2 (77.9) and MgSO4 (66.9) provided protection compared to untreated (51.8). In separate studies, ESR spin trapping with α-phenyl-N-tert-butylnitrone (3 mM PBN) showed that I/R alkoxyl radical production was reduced with MgGl2 (0.0 vs. 2.4 vs. 3.6 mM: 184 vs. 97 vs. 54.8 nM/g tissue × min) to a greater extent than seen with MgSO4 (3.6 mM: 108). Additional studies suggest that Gl1−, unlike SO42−, may scavenge hydroxyl radicals, accounting for the added protection. MgGl2 treated hearts exhibited less postischemic dysfunction and oxidative injury compared to MgSO4, suggesting the contribution of Gl1− to cardioprotection.