Marta Ortí

Reduction of infarct size by the NO donors sodium nitroprusside and spermine/NO after transient focal cerebral ischemia in rats

Nitric oxide (NO) plays a dual role (neuroprotection and neurotoxicity) in cerebral ischemia. NO promoting strategies may be beneficial shortly after ischemia. Therefore, we have studied the hemodynamic and possible neuroprotective effects of two NO donors, the classical nitrovasodilator sodium nitroprusside (SNP) and the NONOate spermine/NO, after transient focal cerebral ischemia in rats. Parietal cortical perfusion was measured by laser-Doppler flowmetry. The effects of increasing intravenous doses (10-300 microgram) of sodium nitroprusside and spermine/NO on cortical perfusion and arterial blood pressure were assessed. Transient (2 h) focal cerebral ischemia was carried out by the intraluminal thread method. The effects of intraischemic intravenous infusion of SNP (0.11, 1.1 mg/kg) and spermine/NO (0.36, 3.6 mg/kg) on hemodynamic parameters and infarct size developed after 1 week reperfusion were assessed. In control conditions, SNP and, to a lesser extent, spermine/NO induced dose-dependent hypotension and concomitant reduction in cortical perfusion. In focal cerebral ischemia, infusion of SNP (0.11 mg/kg) and spermine/NO (0.36, 3.6 mg/kg) reduced the infarct size. In the case of spermine/NO, cortical perfusion was maintained above the control levels during the ischemic insult. No significant hypotension was elicited by NO donors at the dose-ratios infused. In conclusion, brain damage induced by transient focal ischemia is reduced by intravenous NO donors. Neuroprotective effects of spermine/NO are due at least in part to improvement of brain perfusion, while sodium nitroprusside must provide direct cytoprotection. These results give further support to the protective effect of NO in the early stages of cerebral ischemia and point to the therapeutic potential of NONOates in the management of brain ischemic damage.

Relaxant Effects of Sodium Nitroprusside and NONOates in Rabbit Basilar Artery

NONOates are a new class of NO donors that have proven useful for studying the effects of spontaneous and chemically predictable NO release in biologic systems. In order to assess their potential as vasodilatatory drugs in the cerebrovascular bed we have compared the relaxant effects of the classical nitrovasodilator sodium nitroprusside (SNP) and three NONOates, diethylamine/NO complex (DEA/NO), spermine/NO complex (SPER/NO), and diethylenetriamine/NO complex (DETA/NO) in isolated rabbit basilar arteries precontracted with UTP. The 4 NO donors induced full relaxation of the UTP-induced tone, with the following order of potency: SNP > DEA/NO > SPER/NO > DETA/NO. Relaxations induced by SNP and DETA/NO were not modified in rubbed (endothelium denuded) arteries in which acetylcholine-relaxations were almost abolished. On the other hand, relaxations to SNP and SPER/NO were more potent and effective in histamine-precontracted arteries than in KCl-precontracted arteries. Methylene blue significantly inhibited SPER/NO-induced relaxations in both KCl- and histamine-precontracted arteries while SNP-induced relaxations were only slightly inhibited by methylene blue in KCl-precontracted arteries. This study shows that the NO donors SNP, DEA/NO, SPER/NO and DETA/NO have quantitatively different relaxant effects in rabbit basilar arteries according to their rate of NO release. Relaxations are not mediated by endothelial factors, and are inhibited by arterial depolarization. Finally, cGMP formation is involved in relaxation induced by NONOates and much less in SNP-induced relaxation.

Comparative Analysis of the Vascular Actions of Diterpenes Isolated from Euphorbia canariensis

We have analysed the effects of 2,3‐diepiingol 7,12‐diacetate‐8‐isobutyrate (compound 1), ingenol‐3‐angelate‐17‐benzoate (compound 2), ingenol‐3‐angelate‐17‐benzoate‐20‐acetate (compound 3) and 3,5,7,8,9,15‐hexahydroxyjatropha‐6(17),11‐dien‐14‐one‐5,8‐bis(2‐methylbutyrate)‐7‐(2‐methylpropionate) (compound 4), four diterpenes isolated from E. canariensis, on the isometric tension developed by isolated rabbit basilar and carotid arteries.

Effects of cocaine on human and goat isolated cerebral arteries

Cocaine abuse has been increasingly associated with cerebrovascular disease. We have studied the vasoactive properties of cocaine in branches of human middle cerebral artery and in goat middle cerebral artery isolated in an organ bath for isometric tension recording. Cocaine (10(-5) - 3 x 10(-4) M) induced small contractions, while higher concentrations (10(-3) - 3 x 10(-3) M) induced relaxation of human arteries at resting tension. In human arteries precontracted with KCl (50 mM), prostaglandin F- (10(-5) M) or endothelin-1(10(-9) M), cocaine (10(-6) - 3 x 10(-3) M) induced concentration-dependent relaxations which differed in terms of EC50 or maximum effect (Emax). With regard to goat arteries, cocaine (10(-6) - 3 x 10(-3) M) induced almost negligible changes in resting tension, and induced concentration-dependent relaxations of the arterial tone induced with KCl (50 mM). By contrast, goat arteries precontracted with prostaglandin F2 alpha (10(-5) M) or endothelin-1 (10(-9) M) showed biphasic concentration-response curves with concentration-dependent contractions to cocaine (10(-5) - 10(-3) M) and relaxation to the highest concentration (3 x 10(-3) M). Preincubation with cocaine (10(-4) - 10(-3) M) inhibited the contractile responses to CaCl2 (10(-6) - 10(-2) M) in depolarizing, Ca(2+)-free medium, and this inhibition was reversed by preincubation with the Ca2+ entry activator Bay K8644 (10(-10) - 10(-8) M). Therefore, cocaine induces tension changes in cerebral arteries which depend on the species, the arterial tone and the contractile agent inducing it. The relaxant effects could be attributed to the interference of cocaine with the role of Ca2+ in the maintenance of arterial tone, at least in part by blocking Ca2+ entry through membrane channels.

Comparative Relaxant Effects of the NO Donors Sodium Nitroprusside, DEA/NO and SPER/NO in Rabbit Carotid Arteries

1. Sodium nitroprusside (SNP, 10(-9)-3x10(-4) M), diethylamine/NO complex (DEA/NO, 10(-9)-10(-4) M) and spermine/NO complex (SPER/NO, 10(-8)-3x10(-4) M) induced concentration-dependent relaxation of isolated rabbit carotid arteries precontracted with KCl (50 mM) or with histamine (3x10(-6) M). 2. In KCl-precontracted arteries the order of potency was SNP=DEA/NO>SPER/NO, and in histamine-precontracted arteries the order of potency was SNP>DEA/NO>SPER/NO. Relaxations to the three NO donors were significantly higher in histamine-precontracted arteries than in KCl-precontracted arteries. 3. The guanylyl cyclase inhibitor methylene blue (10(-5) M) significantly inhibited relaxations to the three NO donors in histamine-precontracted arteries and, to a lesser extent, in KCl-precontracted arteries. 4. In conclusion, the NO donors SNP, DEA/NO and SPER/NO induce quantitatively different relaxation of rabbit carotid artery. Both, lower relaxant effects in depolarized arteries and inhibition of relaxation by methylene blue indicate the mediation of cGMP formation in the relaxant effects of the three NO donors.

Vasoconstriction to Endothelin-1 in the Goat Middle Cerebral Artery After Transient Global Cerebral Ischemia

We have examined the effects of global ischemia and subsequent reperfusion on the reactivity of goat middle cerebral artery to endothelin-1. The participation of extracellular Ca 2+ in endothelin-1-induced contractions and the ability of the Ca 2+ entry blocker, nicardipine, to counteract them after ischemia were also assessed. Concentration-response curves to endothelin-1 (10 −12 –3×10 −8 mol/L) obtained in arteries from goats subjected to either 5 or 10 minutes of ischemia and 7-day reperfusion did not significantly differ from curves obtained in arteries from sham-operated goats. Concentration-response curves to endothelin-1 in arteries from goats subjected to 20 minutes of ischemia and 7-day reperfusion, however, showed significantly higher pEC 50 (negative logarithm to base 10 of the concentration of endothelin-1 producing 50 of the maximal effects) value ( P max ) values of the concentration-response curves to endothelin-1 were significantly reduced ( P max value was again significantly reduced ( P 2+ -free medium or nicardipine (10 −10 and 10 −8 mol/L), the concentration-response curve to endothelin-1 was significantly inhibited ( P 50 and of E max . In conclusion, there was an increase in the endothelin-1 potency 1 week after 20 minutes of ischemia. At this time, the involvement of dihydropyridine-sensitive L-type Ca 2+ channels in Ca 2+ entry induced by endothelin-1 to develop contraction is reduced when compared with normal arteries. We suggest that the increased reactivity to endothelin-1 could have pathophysiological relevance, and the reduced effect of nicardipine could have therapeutical relevance in cerebral ischemia.

Analysis of rabbit vascular responses to DBI, an ingol derivative isolated from Euphorbia canariensis.

We have analysed the effects of 7,12‐O‐diacetyl‐8‐O‐benzoil‐2,3‐diepiingol (DBI), an ingol derivative isolated from E. canariensis, on isometric tension developed by isolated rabbit basilar and carotid arteries.