Outstanding neuroprotective efficacy of dexrazoxane in mice subjected to sequential common carotid artery sectioning

Antivasoconstrictor effect of the neuroprotective agent dexrazoxane in rat aorta

Dexrazoxane is used clinically to reduce the cardiotoxicity of anthracycline cancer chemotherapeutic agents, acting by an iron-chelating antioxidant mechanism. In a study designed to explore the possible mechanism of the recently described neuroprotective effect of the drug in cerebral ischemia, its influence on vascular reactivity was determined in rat aortic rings. Dexrazoxane was found to be devoid of direct contractile or relaxant activity and to have no influence on responses to acetylcholine or histamine (relaxation), or to angiotensin or serotonin (contraction). In contrast, it decreased contractions to norepinephrine, as evidenced by rightward displacement of the concentration-response curves. The effect was prevented by the removal of the endothelium and by the alpha(2)-adrenoceptor antagonist yohimbine; it was partially antagonized by the endothelium-derived depolarizing factor inhibitor clotrimazole, but was not affected by L-NAME or indomethacin, inhibitors of endothelial nitric oxide and prostacyclin production. The anti-contractile effect did not occur in rings stimulated with the alpha(1)-adrenoceptor agonist phenylephrine. It was concluded that dexrazoxane opposes norepinephrine vascular contraction by enhancing endothelial alpha(2)-adrenoceptor-mediated release of relaxing factor(s). The drug could thus offset the deleterious vasoconstriction elicited by the increased circulating catecholamines present during cerebral ischemia, and by this mechanism produce neuroprotection.

Altered responsiveness of the guinea-pig isolated ileum to smooth muscle stimulants and to electrical stimulation after in situ ischemia

1. We evaluated changes in contractility of the guinea-pig isolated ileum, using intact segments and myenteric plexus-longitudinal muscle (MPLM) preparations, after several times (5-160 min) of ischemia in situ. 2. Intestinal ischemia was produced by clamping the superior mesenteric artery. Ischemic and nonischemic segments, obtained from the same guinea-pig, were mounted in organ baths containing Krebs-bicarbonate (K-B) solution, maintained at 37 degrees C and gassed with 95% O2/5% CO2. The preparations were allowed to equilibrate for 60 min under continuous superfusion of warm K-B solution and then electrically stimulated at 40 V (0.3 Hz, 3.0 ms). Thereafter, complete noncumulative concentration-response curves were constructed for acetylcholine (ACh), histamine (HIS), potassium chloride (KCl), and barium chloride (BaCl2). Mean Emax (maximal response) values were calculated for each drug. 3. Our study shows that alterations of chemically and electrically evoked contractions are dependent on ischemic periods. It also demonstrates that contractile responses of ischemic tissues to neurogenic stimulation decreases earlier and to a significantly greater extent than the non-nerve mediated responses of the intestinal smooth muscle. Contractile responses to smooth muscle stimulants were all similarly affected by ischemia. Electron microscopy images indicated necrotic neuronal death. The decrease in reactivity of ischemic tissues to electrical stimulation was ameliorated by dexrazoxane, an antioxidant agent. 4. We consider the guinea-pig isolated ileum as a useful model system to study the processes involved in neuronal ischemia, and we propose that the reduction in maximal responses to electrical stimulation is a useful parameter to study neuroprotection.

A simplified procedure for the quantitative measurement of neurological deficits after forebrain ischemia in mice

This study describes a comprehensive method to assess neurological deficits after brain ischemia produced by sequential common carotid artery sectioning (SCAS) in aged mice, and a scale to determine the degree of functional incapacity of ischemic animals. The method involves an initial phase of undisturbed observation and a later manipulative phase during which each animal is subjected to a sequence of very simple manipulations. Sham-operated animals demonstrated 96% survival throughout the study period (72 h), whereas the 24, 48 and 72 h survival rates of SCAS-mice were 48, 38 and 36%, respectively. In the surviving SCAS-mice, we detected a total of 23 neurological alterations throughout the observation period (72 h); the most frequent alterations were: motor incoordination, abnormal body position, hypomobility, decreased body tone and muscular strength, tremor, hunched back, passivity, forelimb flexion and ataxic gait. Based on these alterations, we used a global scale that comprises 10 progressive grades beyond 0 (normal), extending to status 10 (death due to SCAS), with higher scores indicating greater deficit. The median neurological scores for sham-operated animals were 1.36, 1.48 and 1.32 at 24, 48 and 72 h, respectively, whereas total neurological scores in SCAS-mice of 6.1, 6.8 and 7.4, at 24, 48 and 72 h, respectively, were substantially greater than those observed in sham-operated animals. The simplicity of the procedure, herein described, to measure the functional neurological condition of ischemic animals, and the remarkable level of functional impairment produced by SCAS offer the possiblity to test the efficacy of putative stroke therapies and to monitor progress of deficits over time in groups of animals.