Characterization of the potent combined endothelin(A/B)-antagonist PD 142893 on cerebral vessels

Abstract

A disturbed balance between endothelin (ET)-1 and nitric oxide (NO) seems to play a key role in the development of delayed cerebral vasospasm following subarachnoidal hemorrhage. Therefore, the effect of PD 142893 one of the first potent ET(A)- and ET(B)-receptor antagonists was characterized on the contraction and relaxation induced by ET-1 and bigET-1 on rat basilar artery (BA). Concentration-effect curves (CECs) were constructed by cumulative application of ET-1 or big ET-1 on BA ring segments with (E+) and without (E–) functionally intact endothelium. The effect of PD 142893 was determined by the modified pK_b value and the shift between the CECs. PD 142893 inhibited the contraction by ET-1 and bigET-1. The pK_b-values were for ET-1: 5.17 (E+) and 5.15 (E–) and for big ET-1: 5.34 (E+) and 5.57 (E–), respectively. A significant relaxation of pre-contracted segments by ET-1 or big ET-1 was neither observed in the presence nor in the absence of the receptor antagonist. The present data suggest a competitive inhibition of the ET(A)-receptor mediated contraction of cerebral arteries by PD 142893. The ET(B)-dependent relaxation of the cerebrovasculature is inhibited by PD 142893 at least in a comparable amount of contraction.     

Lack of substantial effect of the H(3)-antagonist thioperamide and of the non-selective mixed H(3)-antagonist/H(1)-agonist betahistine on amygdaloid kindled seizures

We investigated whether some histamine H(3)-antagonists would attenuate amygdaloid kindled seizures in rats. Thioperamide, a standard H(3)-antagonist, did not significantly reduce either seizure ranks or afterdischarge duration (ADD). Betahistine which has both H(3)-antagonistic activity and H(1)-agonistic activity significantly reduced ADD, albeit mild at a toxic dose, though seizure ranks were not affected. In addition, L-histidine, the precursor of histamine, affected neither seizure ranks, nor ADD. It was shown that H(3)-antagonists have no significant inhibitory action against amygdaloid kindled seizures, probably because released histamine was unable to inhibit those seizures.     

Effects of endothelin on blood vessels of the brain and choroid plexus

Endothelin is a recently described vasoactive peptide produced by endothelial cells. Receptors for endothelin are found throughout the brain, and are particularly dense in the choroid plexus. Effects of endothelin on cerebral blood flow and blood flow to the choroid plexus are not known. In this study, we examined effects of endothelin (100 and 1000 ng/kg i.v.) on regional blood flow (microspheres) and cerebral microvascular pressure in anesthetized rabbits. Endothelin (1000 ng/kg) produced only a 4 +/- 2 mm Hg (mean +/- S.E.M.) increase in systemic blood pressure, and had no effect on cerebral blood flow or cerebral microvascular pressure. In contrast, endothelin produced a marked decrease in blood flow to the choroid plexus and dura mater. Blood flow to choroid and dura remained significantly decreased 1 h after administration of the peptide. Endothelin also reduced blood flow to the kidney and small intestine, but the decreases tended to be less than in choroid plexus or dura mater. Thus, circulating endothelin, at doses that have no effect on cerebral blood vessels, has marked effects on blood flow to the choroid plexus. These findings suggest that circulating or locally produced endothelin may contribute to regulation of brain fluid balance through effects on choroid plexus and production of cerebrospinal fluid.     

A selective endothelin ET(A) receptor antagonist, SB 234551, improves cerebral perfusion following permanent focal cerebral ischemia in rats

In recent experimental studies, a selective antagonist of endothelin ET(A) receptors, SB 234551, improved neurological and histological outcome in both head trauma and transient focal cerebral ischemia. The present study was conducted to ascertain the degree to which hemodynamic alterations are responsible for this therapeutic effect in a model of permanent middle cerebral artery occlusion (MCAo) in rats. Anesthetized Sprague-Dawley rats were subjected to permanent MCAo by insertion of an intraluminal nylon suture coated with poly-L-lysine. The agent (SB 234551, 30 microg/kg/min = 1.8 mg/kg/h) or vehicle (PBS; 0.6 ml/h) was administered by i.v. infusion beginning 15 min after onset of MCAo and lasting for 23.75 h. Autoradiographic measurement of local cerebral blood flow (lCBF) was performed at 24 h. Physiological data were similar among groups. SB 234551 augmented perfusion by 1.7- to 1.8-fold in both the ischemic hemisphere and in the contralateral (non-ischemic) hemisphere when compared to vehicle-treated ischemic animals. In the ischemic hemisphere, the brain regions significantly benefited were those lying outside the zone of most dense ischemia (i.e., paramedian cortex and thalamus), while in the non-ischemic hemisphere all regions measured showed significant lCBF augmentation. This study demonstrates that SB 234551 therapy results in significant improvement of local cerebral perfusion in the ischemic as well as in the non-ischemic hemispheres after permanent MCAo.     

A histochemical study on the innervation of cerebral blood vessels in the bullfrog

Specific histochemical techniques for the demonstration of catecholamine and acetylcholinesterase have been used to study the distribution of adrenergic and cholinergic nerves on the cerebral blood vessels of bullfrog, Rana catesbeiana. The adrenergic nerve meshworks on the cerebral arteries of bullfrog were less dense, had a more elongate appearance along the arterial axis as compared with those of mammals and were rather similar to those of snakes. The nerve plex-uses on the cerebral carotid artery and its main branches were somewhat denser than those on the basilar artery. The most characteristic feature of innervation in the bullfrog cerebral vessels was that no acetylcholinesterase-positive fibres were observed on the extraparenchymal arteries, whereas, in all higher vertebrates investigated so far, the cerebral arteries have been found to be dually innervated although differences in the density of innervation of the two nerves may exist. This suggests that the peripheral adrenergic innervation on the cerebral blood vessels appeared earlier than the cholinergic one in the evolution of vertebrates. On the other hand, both adrenergic and acetylcholinesterase-positive fibres were observed in close contact with parenchymal arterioles and capillaries suggesting the possible existence of a dual central innervation. This feature, however, was by no means common. Thus, the central neurons have a significant influence on the cerebral circulation in the bullfrog is somewhat equivocal. Most of the pial and the parenchymal small vessels and the parenchymal capillaries exhibited a heavy acetylcholinesterase activity on the vascular walls. Although the significance of the enzyme is obscure as yet, this has to be considered in relation to the regulatory mechanism of the cerebral circulation.     

A histochemical study of cerebral cortical vessels and ganglionic vessels of the caudatoputamen in aging normotensive rats

The goal was to describe the metabolic profile of ganglionic and cortical arteries and arterioles in aging normotensive male rats. Five enzymes indicative of key metabolic pathways in the vessel walls were semiquantitatively evaluated using bright-field histochemical microscopy. Lactate dehydrogenase showed significant reactivity which increased with vessel diameter in cortical and ganglionic vessels in all age groups tested. Succinate dehydrogenase and cytochrome oxidase showed little reactivity in both cortical and ganglionic vessels, suggesting a reduced role for aerobic metabolic pathways. Myosin ATPase reactivity was high in cortical and ganglionic vessels. Only this enzyme showed an increased reactivity that was correlated with the age and diameter of the vessel. Glucose-6-phosphate dehydrogenase reactivity was more pronounced in cortical than ganglionic vessels, suggesting that the hexose-monophosphate-shunt may be more active in the cortical vessels. There were no regional differences in enzyme reactivity throughout the caudatoputamen. In conclusion, both the cortical and ganglionic vessels are metabolically active, with significant anaerobic glycolysis, and reduced, but observable capacity for aerobic metabolism. The decreased myosin ATPase reactivity and the low level of glucose-6-phosphate dehydrogenase reactivity in the ganglionic arterioles of senescent rats may contribute to the susceptibility of these vessels to cerebrovascular accidents.     

Caffeinated clues and the promise of adenosine A(2A) antagonists in PD

Large prospective epidemiologic studies have linked the consumption of coffee and other caffeinated beverages to a reduced risk of subsequently developing PD. Caffeine as well as more specific antagonists of the adenosine A(2A) receptor have also now been found to attenuate neurotoxicity in a mouse model of PD. The convergence of these epidemiologic and laboratory data supports the possibility that caffeine may reduce the risk of developing PD. However, a neuroprotective effect of caffeine in PD remains unproven; current evidence does not provide a rational basis for recommending caffeine consumption to modify the risk or progression of PD. In addition to possessing neuroprotective potential, caffeine and other A(2A) antagonists have long been known to acutely reverse motor deficits in a variety of PD models. This symptomatic antiparkinsonian benefit of blocking A(2A) receptors, coupled with their remarkably restricted expression in the basal ganglia, have made A(2A) antagonists attractive targets for drug development. Now, with the prospect of a neuroprotective bonus, the novel therapeutic potential of A(2A) antagonists appears all the more promising just as they are entering clinical trials for PD.     

Influence of estrogens on the impedance of cerebral blood vessels

BACKGROUND AND PURPOSE: Recent experimental research has demonstrated the neuroprotective effect of estrogen on the ischemic brain. There is, however, little data available concerning the effects of estrogen on cerebral circulation in humans. In this contribution we studied the influence of endogenous estrogen on the flow in the carotid arteries and on the cerebrovascular impedance. MATERIALS AND METHODS: The plasma concentration of 17-beta-estradiol was measured in 19 healthy, young women over 10 days of the menstrual cycle (days 3, 6, 10, 13-17, 20 and 24). Ultrasound examination of the carotid arteries was performed on the same days using a Toshiba Aplio ultrasound system endowed with a 7.5 MHz linear transducer. Impedance indices based on the recorded systolic, mean and end-diastolic blood flow velocities were calculated for the internal, common and external carotid arteries. RESULTS: During the follicular phase of the menstrual cycle, blood flow in the internal carotid artery increased considerably in all subjects along with increasing plasma concentrations of estrogen. The end-diastolic blood flow velocity increased most significantly, on average by 16% and by up to 24% in individual cases. At the same time, the impedance indices (resistance index--RI and pulsatility index--PI) decreased significantly from their base values. Blood flow velocity in the common carotid artery, the caliber of this vessel, pulse rate and blood pressure remained stable during the entire follicular phase of the cycle. Nevertheless, the flow velocity in the external carotid artery decreased. This suggests that an increase in the cerebral blood flow, promoted by decreasing cerebro-vascular impedance in the follicular phase of the cycle, occurs at the expense of blood "stolen" from the external carotid artery. CONCLUSION: Estrogen increases blood flow in the internal carotid artery by decreasing the impedance of cerebral microcirculation.     

Association between migraine and endothelin type A receptor (ETA -231 A/G) gene polymorphism

BACKGROUND: Previous studies have described an association between migraine and endothelin, a potent vasoconstrictor. OBJECTIVE: To test the association between migraine and gene polymorphisms of the endothelin system. METHODS: A population-based study of elderly individuals (n = 1,188) in Nantes (western France) was conducted. Lifetime migraine was defined according to the International Headache Society criteria, after an interview with a headache specialist. Five polymorphisms in genes encoding endothelin 1, endothelin type A (ET(A)), and type B receptors were determined in more than 90% of the sample. RESULTS Migraine was diagnosed in 140 participants (11.9%). The ETA (-231 A/G) polymorphism was the only polymorphism significantly associated with migraine. There was a trend of decreasing prevalence of migraine with number of copies of the G allele (AA genotype: 15.7% of participants with migraine, AG: 9.7%, GG: 2.9%; p < 0.001). Carrying the G allele was associated with a sex- and age-adjusted odds ratio of 0.50 (95% CI, 0.34 to 0.74). The association was observed in both sexes and was stronger in participants with a family history of severe headaches than in those without. CONCLUSIONS: A variant of the ET(A) receptor gene modulates the risk for migraine. These results offer new insights into the pathophysiology of the vascular component of migraine.     

节段性脊髓运动诱发电位的初步研究

对23例正常受试者进行了节段性脊髓运动诱发电位的初步研究。确立了节段性棘突间刺激,在双胫前肌群记录的节段性脊髓运动诱发电位技术。结果表明:节段性脊髓运动诱发电位波形出现良好,节段性差异显著。     

Immunohistochemical demonstration of APP (Avian Pancreatic Polypeptide)-immunoreactive nerve fibres around cerebral blood vessels

Nerve fibres containing immunoreactive avian pancreatic polypeptide (APP) were demonstrated in the wall of cerebral blood vessels from several species. Pial arteries of chicken, mouse, rat, guinea-pig, cat and dog had a dense supply of APP fibres while APP fibres were less numerous in rabbit, cow and monkey. The APP-immunoreactive fibres were more numerous in the rostral part of the circle of Willis than around more caudally located pial vessels. Immunoreactive fibres were also seen in the wall of pial vessels of the spinal cord, as shown in the cat. Extirpation of the superior cervical sympathetic ganglion was followed by a marked reduction in the number of APP-containing fibres on the ipsilateral side of the brain.     

Effects of endothelin B receptor agonists on amyloid beta protein (25-35)-induced neuronal cell death

MPTP or its metabolite MPP+ are used to produce a Parkinsonism syndrome in a variety of animal species. The present study describes the effects of intranigral MPP+ administration either at 10 or 40 microg on the neuronal dopamine transporter (DAT) activity measured in rat striatal synaptosomes at different times after lesion. The 40 microg MPP+ injection induced a maximal toxic effect on day 7. However, 10 microg MPP+ progressively inhibited DA uptake on the injured side. V(max) decreased in a time-dependent manner and the lowest value was observed on day 21 after lesion. At this time, the K(m) value began to increase and was continuously accentuated until day 45 as compared to the contralateral side. Treatments either with the antioxidant alpha-tocopherol acetate or the MAO inhibitor pargyline, given daily for 7 days after lesion, partially prevented the 40 microg MPP(+)-induced inhibition of DA uptake. Conversely, both treatments given daily for 21 days after lesion completely prevented the alteration of DAT activity in the ipsilateral striatum induced by 10 microg MPP+. The absence of protection when both treatments were stopped 2 weeks before DA uptake measurements indicated that free radicals and DA oxidized products were continuously accumulated and gradually affected the functionality of the DAT. These results demonstrate that a rat intranigral lesion with 10 microg MPP+ led to a progressive impairment of DAT activity.     

Nicotine reduces A beta in the brain and cerebral vessels of APPsw mice

Ten days treatment with nicotine reduced insoluble amyloid A beta 1-40 and Alpha beta 1-42 peptides by 80% in the cortex of 9-month-old APPsw mice, which is more than that observed in 14.5-month-old mice following nicotine treatment for 5.5 months. A reduction in A beta associated with cerebral vessels was observed in addition to that deposited as parenchymal plaques after 5.5 months treatment. The diminution in A beta peptides observed was not accompanied by changes in brain alpha, beta or gamma secretase-like activities, NGF or BDNF protein expression measured in brain homogenates. A significant increase in sAPP was observed after nicotine treatment of SH-SY5Yneuroblastoma cells that could be blocked by the nicotinic antagonist mecamylamine. Attenuation of elevated [(125)I]-alpha bungarotoxin binding (alpha 7) in APPsw mice was observed after 5.5 months nicotine treatment. Both these observations suggest that the reduction in insoluble A beta by nicotine might be in part mediated via the alpha 7 nicotinic receptor. Further studies are required to identify potential mechanisms of the nicotine's amyloid-reducing effect.     

颈内静脉血浆ET、NO变化与脑缺血再灌注损伤相关性研究

目的观察兔全脑缺血再灌注(I/R)期间颈内静脉血浆ET、NO的动态变化及它们与脑I/R损伤的关系。方法取清洁级家兔24只,随机分A、B、C3组,每组8只,缺血15min后分别再灌注30min(A组),2h(B组)和4h(C组),C组在缺血前15min(I0)及再灌注30min(R1)、2h(R2)、4h(R3)4个时点、B组在前3个时点、A组在前2个时点采颈内静脉球部血样分别测定ET、NO及计算ET/NO比值;取左颞皮质作HE、尼氏体染色,光镜观察,对神经元进行图像分析,测量核截面积和尼氏体平均光密度。结果(1)与I0比较,NO在R1时显著增加(P<0.01),在R2、R3时缓慢下降;ET在R1~R3时持续上升,由317.58ng/L升至637.01ng/L;在R1时ET/NO比值与I0比较差异无显著性,在R2、R3时比值显著增大,由44.83×10-6升至224.30×10-6;(2)B、C组的病理损伤比A组严重,C组又比B组严重;B、C组的神经元核截面积比A组显著降低,C组的核截面积最小;尼氏体平均光密度A>B>C组;(3)ET分别与核截面积及尼氏体平均光密度呈显著负相关;ET/NO比值与核截面积及尼氏体平均光密度呈非常显著负相关;结论ET增加及ET与NO之间平衡的破坏可能是脑I/R损伤的主要原因之一;检测颈内静脉血ET和NO的动态变化可以反映脑I/R损伤程度。