Francisco J. Miranda

Comparison of the anticonstrictor action of dihydropyridines (nimodipine and nicardipine) and Mg2+ in isolated human cerebral arteries

The isometric tension recorded from ring segments of branches of human middle cerebral artery was the parameter used to study the inhibition of spasmogen-induced contractions as model for cerebral vasospasm. Concentration-response curves to 5-hydroxytryptamine (10(-9)-3 x 10(-5) M) and prostaglandin F2 alpha (10(-7)-3 x 10(-5) M) were inhibited in Ca(2+)-free medium and in Ca(2+)-free medium to which EGTA (1 mM) had been added, respectively. Nimodipine (10(-7), 10(-5) M), nicardipine (10(-7), 10(-5) M) and Mg2+ (magnesium sulfate 10(-4), 10(-2) M) inhibited the 5-HT-elicited contractions, and this inhibition was similar for the highest concentrations tested. In contrast, nimodipine and nicardipine were more effective than Mg2+ to inhibit the prostaglandin F2 alpha-elicited contractions. Nimodipine (10(-9)-10(-5) M), nicardipine (10(-9)-10(-5) M) and Mg2+ (10(-5)-3 x 10(-2) M) relaxed the arteries precontracted with PGF2 alpha (10(-5) M), but nicardipine was the most potent relaxant drug. Because 5-hydroxytryptamine and prostaglandin F2 alpha may be involved in the pathogenesis of cerebral vasospasm, nimodipine, nicardipine, and Mg2+ could be used in the pharmacological treatment of this disorder. However, dihydropyridines (particularly nicardipine) are more potent anticonstrictors than Mg2+.

Impairment of the modulatory role of nitric oxide on the endothelin-1-elicited contraction of cerebral arteries: a pathogenetic factor in cerebral vasospasm after subarachnoid hemorrhage?

OBJECTIVE Nitric oxide (NO) and endothelin-1 (ET-1) are two endothelium-derived factors probably involved in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH). Our aim was twofold, i.e., to ascertain whether endothelial and nonendothelial NO modulates the contractile response of cerebral arteries to ET-1 and to analyze whether this relationship might be impaired after experimental SAH. METHODS Rings of middle cerebral artery from goats in the control group and from goats with SAH were set up for isometric tension recordings. SAH was induced 3 days before the experiments by infusion of 10 ml of autologous arterial blood through a catheter previously inserted into the subarachnoid space (basal cistern). In goats in the control group, the response to ET-1 was obtained as follows: 1) in control arteries (unrubbed and nonincubated arteries); 2) in rubbed arteries (arteries in which the endothelium was mechanically removed); 3) during incubation with NG-nitro-L-arginine (L-NOArg) alone or plus L- or D-arginine; and 4) in rubbed arteries plus incubation with L-NOArg. In goats with SAH, that response was obtained in control arteries, rubbed arteries, and during incubation with L-NOArg. Specimens of middle cerebral artery were processed for transmission electron microscopy study. RESULTS In goats in the control group, ET-1 elicited concentration-dependent contraction of the middle cerebral artery that was significantly potentiated after endothelium denudation or during incubation with L-NOArg. The latter effect was reversed by L-arginine but not by D-arginine. Combined endothelium denudation and incubation with L-NOArg produced a contractile response to ET-1 significantly higher than that induced by each treatment separately. Hyperreactivity to ET-1 was observed in goats with SAH. Endothelium denudation did not alter the enhanced response to ET-1, but it was further significantly increased after incubation with L-NOArg. CONCLUSION These results demonstrate that an ET-1-NO interaction exists in control cerebral arteries in such a way that endothelial and nonendothelial NO partially counteract the contractile response to ET-1 and that although SAH did not modify the effect of nonendothelial NO, the absence of endothelial NO after SAH may contribute to the hyperreactivity of cerebral arteries to ET-1 and, thereby, to the development of cerebral vasospasm.

Changes in the Cerebrovascular Effects of Endothelin-1 and Nicardipine after Experimental Subarachnoid Hemorrhage

The role of endothelium-related factors in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH) has gained interest since the discovery of endothelin-1 (ET-1). We have examined, before and after SAH, the responsiveness of the cerebrovascular bed of the goat to ET-1, the sources of Ca2+ in ET-1-induced responses, and the ability of the Ca2+ entry blocker nicardipine to counteract them. Before SAH, injection of ET-1 into the cerebral circulation increased cerebrovascular resistance, thereby producing dose-dependent reductions in cerebral blood flow (CBF), which were prevented by nicardipine. In isolated middle cerebral arteries, ET-1 induced concentration-dependent contractions, which were equally inhibited in Ca(2+)-free medium (without or with ethylene glycol tetraacetic acid) and by the Ca2+ entry blocker nicardipine. On the third day after SAH, CBF was reduced by 28% and cerebrovascular resistance increased by 39%. At the same time, both ET-1-induced reductions in CBF and the constricting effects of ET-1 in vitro were enhanced. The ability of nicardipine to increase CBF and to inhibit the effects of ET-1 was impaired as a result of reduced dependence of cerebral arteries on extracellular Ca2+. On the seventh day after SAH, CBF and cerebrovascular resistance returned to control values, and effects of ET-1 became normal. It is suggested that the hyperreactivity to ET-1 of the cerebrovascular bed induced by SAH could have a role in the development of vasospasm, which could reduce the vascular effects of Ca2+ entry blockers after SAH.

Experimental diabetes induces hyperreactivity of rabbit renal artery to 5-hydroxytryptamine.

The influence of diabetes on the response of isolated rabbit renal arteries to 5-hydroxytryptamine (5-HT) was examined. 5-HT induced a concentration-related contraction that was higher in arteries from diabetic rabbits than in arteries from control rabbits. Endothelium removal did not significantly modify 5-HT contractions in arteries from control rabbits but enhanced the response to 5-HT in arteries from diabetic rabbits. Incubation with N(G)-nitro-L-arginine (L-NA) enhanced contractions to 5-HT in arteries from control and diabetic rabbits. In arteries with endothelium, this L-NA enhancement was lower in diabetic rabbits than in control rabbits. In arteries without endothelium, incubation with L-NA enhanced the maximal contractions to 5-HT in control rabbits but did not in diabetic rabbits. Indomethacin inhibited 5-HT-induced contraction of arteries from control rabbits and enhanced the maximal contraction to 5-HT of arteries from diabetic rabbits. In summary, diabetes enhances contractile response of rabbit renal artery to 5-HT. In control animals, this response is regulated by both endothelial and non-endothelial (neuronal) nitric oxide (NO) and by a vasoconstrictor prostanoid. Diabetes impairs the release of non-endothelial NO and the vasoconstrictor prostanoid.

Effects of endothelin-1 on the cerebrovascular bed of the goat

The aim of the present study was to analyze the effects of endothelin-1 (ET-1) in the cerebrovascular bed of the goat, the importance of endothelial integrity and the contribution of extracellular Ca2+ to these responses. We measured isometric tension and 45Ca2+ uptake in isolated middle cerebral arteries, and cerebral blood flow (CBF) in unanesthetized animals. ET-1 elicited concentration-dependent contractions which were potentiated in arteries without endothelium. Ca2(+)-free medium and nicardipine inhibited, and Bay K 8644 potentiated the ET-1-induced contractions. ET-1 enhanced 45Ca2+ uptake in isolated arteries. Injections of ET-1 directly into the cerebral circulation decreased CBF and increased cerebrovascular resistance in a dose-dependent manner. Infusion of nicardipine inhibited the ET-1-induced reductions in CBF. These results suggest that ET-1 reduces CBF of goats because of contraction of cerebral arteries by a direct action on smooth muscle, which is modulated by the endothelium and depends partially on the activation of Ca2+ influx through dihydropyridine-sensitive channels.

Diabetes-induced changes in endothelial mechanisms implicated in rabbit carotid arterial response to 5-hydroxytryptamine

The influence of diabetes on endothelial mechanisms implicated in the response of isolated rabbit carotid arteries to 5-hydroxytryptamine (5-HT) was studied. 5-HT induced a concentration-dependent contraction that was potentiated in arteries from diabetic rabbits with respect to that in arteries from control rabbits. Endothelium removal potentiated 5-HT contractions in arteries from both control and diabetic rabbits but increased the maximum effect only in arteries from diabetic rabbits. Incubation of arterial segments with N(G)-nitro-L-arginine (L-NA) enhanced the contractile response to 5-HT. This L-NA enhancement was greater in arteries from diabetic rabbits than in arteries from control rabbits. Aminoguanidine did not modify the 5-HT contraction in arteries from control and diabetic rabbits. Indomethacin inhibited the 5-HT-induced response, and this inhibition was higher in arteries from control rabbits than in arteries from diabetic rabbits. In summary, diabetes enhances the sensitivity of the rabbit carotid artery to 5-HT. In control animals, the endothelium modulated the arterial response to 5-HT by the release of both nitric oxide (NO) and a vasoconstrictor prostanoid. Diabetes enhances endothelial constitutive NO activity and impairs the production of the endothelial vasoconstrictor.

Different Effects of Mg2+ on Endothelin-1− and 5-hydroxytryptamine-elicited Responses in Goat Cerebrovascular Bed

Mg2+ influences the response of cerebral arteries to several agonists, but until now its effects on endothelin-1 (ET-1) had not been studied. We recorded and compared the responses of goat cerebrovascular bed to ET-1 and 5-hydroxytryptamine (5-HT) during various Mg2+ treatments. We performed experiments in vitro by recording isometric tension in isolated goat middle cerebral arteries and in vivo by recording cerebral blood flow (CBF) and other physiologic parameters in conscious goats. Cumulative addition of ET-1 (10(-11)-3 x 10(-8) M) and 5-HT (10(-9) -10(-5) M) contracted cerebral arteries concentration dependently in bath media containing 0 (Mg(2+)-free medium), 1 (control), and 10 mM Mg2+, but the influence of Mg2+ was different: Mg2+ deprivation increased sensitivity (EC50) and Mg2+ overload reduced contractility (Emax) of cerebral arteries to 5-HT, whereas the ET-1 response did not change in these conditions. Cumulative addition of Mg2+ (10(-4)-3 x 10(-2) M) at the active tone induced by ET-1 (10(-9) M) and 5-HT (10(-5) M) elicited concentration-dependent relaxations of cerebral arteries, but the relaxant response was lower at the ET-1 precontraction. Infusions of ET-1 (0.1 nmol/min) and 5-HT (10 micrograms/min) directly into the cerebroarterial supply of the unanesthetized goats elicited a sustained decrease in CBF and an increase in cerebral vascular resistance. Magnesium sulfate, administered as increasing doses (10-300 mg) in the same way increased CBF and decreased cerebral vascular resistance, although this effect was less on ET-1-induced than on 5-HT-induced cerebral vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetes potentiates acetylcholine-induced relaxation in rabbit renal arteries

The response of rabbit renal arteries to acetylcholine and its endothelial modulation in diabetes were investigated. Acetylcholine induced concentration-related endothelium-dependent relaxation of renal arteries that was significantly more potent in diabetic rabbits than in control rabbits. Pretreatment with N(G)-nitro-L-arginine (L-NOArg), indomethacin, or L-NOArg plus indomethacin induced partial inhibition of acetylcholine-induced relaxation. Inhibition induced by L-NOArg plus indomethacin was significantly higher in arteries from diabetic rabbits than in arteries from control rabbits. In renal arteries depolarised with KCl 30 mM and incubated with L-NOArg plus indomethacin, acetylcholine-induced relaxation was almost abolished in both groups of rabbits and this response was not different from that obtained in arteries without endothelium. Sodium nitroprusside induced concentration-dependent relaxation of renal arteries from control and diabetic rabbits without significant differences between the two groups of animals. These results suggest that diabetes potentiates the acetylcholine-induced relaxation in rabbit renal arteries. Increased release of nitric oxide and prostacyclin could be responsible for the enhanced relaxant potency of acetylcholine in diabetes.

Modulatory role of endothelial and nonendothelial nitric oxide in 5-hydroxytryptamine-induced contraction in cerebral arteries after subarachnoid hemorrhage.

OBJECTIVE Endothelial dysfunction is claimed to play a role in the pathogenesis of delayed cerebral vasospasm after subarachnoid hemorrhage (SAH). We have examined the effect of experimental SAH on the modulatory action of endothelial and nonendothelial nitric oxide (NO) in the contractile response of goat middle cerebral artery to 5-hydroxytryptamine (5-HT). METHODS We compared the 5-HT-induced contractile responses of cerebral arteries from control goats and from goats with SAH that had been experimentally induced 3 days earlier by delivery of autologous arterial blood into the subarachnoid space. Contractile responses were examined by recording the isometric tension in isolated cerebral arteries. To assess the influence of endothelium, this cell layer was mechanically removed in some of the arteria, segments (rubbed arteries) from both control goats and goats with SAH. RESULTS In arteries from control goats, contractile responses to 5-HT were significantly higher in rubbed arteries than in arteries with intact endothelium; 5-HT-induced contractions were significantly enhanced by a competitive inhibitor of NO synthesis, NG-nitro-l-arginine, in arteries both with and without endothelium. In arteries from goats with SAH, 5-HT contracted cerebral arteries without showing significant differences between segments with endothelium and those that had been rubbed; in both cases, 5-HT-induced contractions were significantly higher than those obtained in arteries from control goats. NG-Nitro-l-arginine significantly enhanced the contractile response to 5-HT of cerebral arteries from goats with SAH. CONCLUSION These results suggest that cerebral arteries after SAH exhibit hyperreactivity to 5-HT via a mechanism that involves the absence of the modulatory role of endothelial NO, that SAH does not modify the modulatory role of nonendothelial NO, and that impairment of the modulatory action of endothelial NO on vascular responses to 5-HT could contribute to the pathogenesis of cerebral vasospasm after SAH.

Soy-derived phytoestrogens as preventive and acute neuroprotectors in experimental ischemic stroke: Influence of rat strain

The ability of a soy-based high-phytoestrogen diet (nutritional intervention) or genistein (pharmacological intervention), to limit ischemic brain damage in Wistar, Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats, has been assessed. As to the nutritional intervention, two groups from each strain received either a phytoestrogen-free (PE-0) or a high-phytoestrogen (PE-600) diet from weaning to adulthood. As to the pharmacological intervention, all animals were fed the standard soy-free AIN-93G diet and subsequently separated into two groups from each strain to receive either pure genistein (aglycone form, 1mg/kg/day intraperitoneal) or vehicle at 30 min reperfusion. After an episode of 90 min ischemia (intraluminal thread procedure) followed by 3 days reperfusion, cerebral infarct volume was measured. Arterial blood pressure (ABP) was significantly higher at the basal stage (just before ischemia) in SHR (140 ± 7 mmHg, n=17, p<0.05) than in Wistar (113 ± 4mmHg, n=23) and WKY (111 ± 6mmHg, n=14) rats. No significant differences were shown among the three stages (basal, ischemia, reperfusion) within each rat strain for both PE-0 and PE-600 diets. Wistar, but not WKY or SHR, rats fed the PE-600 diet showed significantly lower infarct volumes than their counterparts fed the PE-0 diet (30 ± 3% vs. 17 ± 3%, p<0.01). Genistein-treated Wistar, but not WKY or SHR, rats showed significantly lower infarct volumes than their vehicle-treated controls (27 ± 2% vs. 15 ± 2%, p<0.01). Our results demonstrate that: (1) the neuroprotective action of either chronic or acute exposure to soy isoflavones is strain-dependent, since it was shown in Wistar but not WKY or SHR rats; and (2) the soy-based diet does not prevent development of hypertension in SHR rats.