mtt-formazan and Myocardial-Ischemia

The effect of Bis(2-chloroethoxy)methane (CEM) on myocardial response to ischemia was tested in rats. CEM was dermally applied for 3 days to F344/N male rats, at 0, 100, 400, or 600 mg/kg/d. Subsequently, left ventricular sections were prepared from each rat heart. Part of the sections from each heart were exposed to 90 minutes of simulated ischemia, followed by 90 minutes of reoxygenation. The rest of the sections were continuously oxygenated. Mitochondrial activity was assessed in the sections by the MTT colorimetric assay, reflecting dehydrogenases redox activity. Myocardial toxicity occurred in response to 400 and 600 mg/kg, characterized by myofiber vacuoles, necrosis, and mononuclear infiltrates. The latter dose was lethal. In sections from rats treated with 400 mg/kg CEM, redox activity was decreased by 21% (p<0.01) in oxygenated conditions and by 45% (p<0.01) in ischemia-reoxygenation, compared to controls. Hearts of rats treated with 100 mg/kg/d CEM showed normal histology. Their mitochondrial activity did not differ from that of untreated rat hearts in oxygenated conditions. However, in ischemia-reoxygenation, their redox activity was significantly lower (by 46%, p<0.01) than that of untreated rat hearts. These results demonstrate that subtoxic dosage of a cardiotoxic agent may cause occult cardiotoxicity, reflected by impaired response to ischemia.

Topics: Administration, Topical; Animals; Dose-Response Relationship, Drug; Drug Administration Schedule; Ethyl Ethers; Female; Formazans; Mitochondria, Heart; Myocardial Ischemia; Myocardium; Oxidation-Reduction; Rats; Rats, Inbred F344; Tetrazolium Salts

We sought to investigate the effect of alpha1-adrenoceptor activity on the ischemic and reoxygenated human myocardium.. Right atrial appendages (n = 6 per group) obtained during elective cardiac operations were sliced and stabilized in normoxic normothermic buffer solution for 30 minutes and then subjected to 90 minutes of simulated ischemia, followed by 120 minutes of reoxygenation. In study 1 the dose responses to the alpha1-adrenoceptor agonist phenylephrine (0.01, 0.1, 1, 10, and 100 micromol/L) and to the alpha1-adrenoceptor antagonist prazosin (0.1, 1, 10, and 100 micromol/L) when administered for 10 minutes before ischemia, during ischemia, and during reoxygenation were examined. The influence of the time of administration (ie, before ischemia, during ischemia, or during reoxygenation) of phenylephrine (0.1 micromol/L) and prazosin (10 micromol/L) was then investigated in study 2. In study 3 the effect of the combined administration of phenylephrine given before ischemia and prazosin given during ischemia was investigated. In study 4 the protective effect of phenylephrine given before ischemia (for 10 minutes or for 5 minutes with a 5-minute washout period) was compared with that of ischemic preconditioning (5 minutes of ischemia and 5 minutes of reoxygenation). At the end of each protocol, the leakage of creatine kinase (in units per gram of wet weight) and the reduction of 3-[4,5 dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide to insoluble formazan dye (in millimoles per gram of wet weight) were measured.. Phenylephrine is maximally beneficial at 0.1 and 1 micromol/L (creatinine kinase, 0.97 +/- 0.06 and 0.95 +/- 0.03 U/g, respectively; 3-[4,5 dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide, 153.0 +/- 7.8 and 156.2 +/- 6.7 mmol/g, respectively) compared with ischemic control (creatine kinase, 1.87 +/- 0.03 U/g; 3-[4,5 dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide, 108.5 +/- 6.8 mmol/g; P <.05) but prazosin is detrimental at concentrations above 10 micromol/L (creatine kinase, 5.22 +/- 0.29 U/g; 3-[4,5 dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide, 69.8 +/- 2.9 mmol/g; P <.05 vs ischemic control). In addition, phenylephrine (0.1 micromol/L) is protective when given before ischemia (creatine kinase, 2.06 +/- 0.21 U/g; 3-[4,5 dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide, 148.5 +/- 4.5 mmol/g; P <.05 vs ischemic control) but is detrimental when given during ischemia alone (creatine kinase, 4.49 +/- 0.98 U/g; 3-[4,5 dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide, 70.5 +/- 6.1 mmol/g; P <.05 vs ischemic control) and has no significant effect during reoxygenation. In contrast, prazosin (10 micromol/L) is beneficial when given during ischemia alone (creatine kinase, 1.34 +/- 0.10 U/g; 3-[4,5 dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide, 148.5 +/- 4.5 mmol/g; P <.05 vs ischemic control), is detrimental when given during reoxygenation alone (creatine kinase, 1.5 +/- 0.16 U/g; 3-[4,5 dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide, 85.0 +/- 4.7 mmol/g; P <.05 vs ischemic control), and has no effect when given before ischemia. The use of phenylephrine before ischemia alone is as protective as prazosin given during ischemia alone, but the combination of the two drugs does not cause additional benefit. Interestingly, the protection afforded by phenylephrine when given before ischemia is similar to that obtained with ischemic preconditioning.. In the human myocardium activation of alpha1-adrenoceptors before ischemia is protective but is detrimental during ischemia, whereas blockade of alpha1-adrenoceptors is beneficial during ischemia but detrimental during reoxygenation. The degree of protection achieved by activation of the alpha1-adrenoceptors before ischemia is similar to that obtained with blockade of alpha1-adrenoceptors during ischemia and that of ischemic preconditioning.

Topics: Adrenergic alpha-Antagonists; Creatine Kinase; Formazans; Humans; In Vitro Techniques; Ischemic Preconditioning, Myocardial; Myocardial Ischemia; Myocardium; Phenylephrine; Prazosin; Receptors, Adrenergic, alpha-1; Tetrazolium Salts