Effects of prostanoids on isolated feline cerebral arteries. I. Characterization of the contraction-mediating receptor

The effects of various prostanoids on isolated feline basilar arteries (BA) were studied. Contractions were induced with the following order of potency: U 46619 approximately equal to U44069 greater than PGB2 greater than PGF2 alpha approximately equal to PGA2 approximately equal to PGB1 greater than or equal to PGA1 approximately equal to PGE2 = PGD2 greater than PGF1 alpha approximately equal to TXB2 approximately equal to PGE1 approximately equal to PGD1. Distinct bimodal responses with a relaxation at low concentrations followed by a contraction at high concentrations, were induced by PGA1, PGA2, PGD, and PGE2. None of the tested prostanoids relaxed K+-contracted arteries, and a sizable relaxant effect in PGF2 alpha-contracted arteries could be induced only by PGE1. As judged by the relative order of potency, PG-induced contractions of the feline BA seem to be mediated by a thromboxane sensitive receptor. PGF2 alpha-induced contractions apparently do not involve the release of noradrenaline from perivascular nerves since phentolamine failed to affect contractions induced by this agent.     

Effects of prostanoids on isolated feline cerebral arteries

The roles of extra-and intracellular calcium for the contractile effects of PGF_2α in the feline basilar artery (BA) were investigated. Comparisons were made with contractions induced by K⁺ and noradrenaline (NA). Addition of nifedipine to PGF_2α-or K⁺ (124 mM)-contracted arteries resulted in an incomplete relaxation, whereas NA-contracted vessels were completely relaxed. Incubation of the preparations in a calcium-free medium containing 10^-5 M EGTA for 5–10 min almost abolished contractions induced by K⁺ and NA. In contrast, 63 % of the response to PGF_2α remained after pretreatment of the arteries in a calcium-free solution for 40 min; PGF_2α produced a biphasic contraction in 17 out of 20 preparations consisting of a rapidly developing initial phase followed by a second increase in tension after 1–6 min. The second phase was absent if the EGTA-concentration was increased to 10^-4 M, or if the arteries were pre-treated with nifedipine. After incubation of the arteries in a calcium-free medium for 40–120 min and K⁺-depolarization, re-addition of calcium elicited contractions at lower concentrations in the presence of PGF_2α than in controls. The results suggest that PGF_2α-induced contractions in the feline BA are considerably less dependent on extracellular calcium than contractions evoked by K⁺ or NA. PGF_2α appears to be able to release calcium from two cellular stores, and may also promote calcium influx through the cell membrane.     

Effects of prostanoids on isolated feline cerebral arteries

The effects of various prostanoids on isolated feline basilar arteries (BA) were studied. Contractions were induced with the following order of potency: U 46619 ? U44069 > PGB₂ > PGF_2a? PGA, ? PGB, ≥ PGA, ? PGE₂= PGD₂ > PGF_1a? TXB₂? PGE₁? PGD₁. Distinct bimodal responses with a relaxation at low concentrations followed by a contraction at high concentrations, were induced by PGA₁, PGA₂, PGD, and PGE₂. None of the tested prostanoids relaxed K⁺-contracted arteries, and a sizable relaxant effect in PGF_2a-contracted arteries could be induced only by PGE₁. As judged by the relative order of potency, PG-induced contractions of the feline BA seem to be mediated by a thromboxane sensitive receptor. PGF_2a-induced contractions apparently do not involve the release of noradrenaline from perivascular nerves since phentolamine failed to affect contractions induced by this agent.     

Effects of the thromboxane-receptor antagonist L-636,499 on feline cerebral arteries

The effects of the thromboxane-receptor antagonist L-636,499 on contractions induced by U46619 and prostaglandin (PG)F2 alpha were studied in the isolated feline basilar artery (BA). L-636,499 (10(-6)-3 X 10(-5) mol l-1) shifted concentration-response curves induced by U46619 to the right in a parallel manner. By contrast, concentration-response curves induced by PGF2 alpha were displaced only when L-636,499 concentrations of 10(-5) and 3 X 10(-5) mol l-1 were used. The Schild plot using U46619 as the agonist revealed a slope index (0.69) which was significantly less than unity. PA2-values calculated according to the method of van Rossum differed significantly between different concentration intervals of L-636,499. At 10(-6) to 3 X 10(-6) mol l-1 the PA2-value was 5.99, whereas at 10(-5) to 3 X 10(-5) mol l-1 it was 5.59. Using PGF2 alpha as the agonist the PA2-value at the L-636,499 concentration interval 10(-5) to 3 X 10(-5) mol l-1 was 5.69. It may be concluded that the feline BA contains two receptor sites mediating prostanoid-induced contraction, one of which may be characterized as a thromboxane-sensitive (TP) receptor. L-636,499 can interact with both receptor sites with highest affinity for the TP receptor site.     

The effect of neuropeptide Y on striatal catecholamines

Neuropeptide Y and peptide YY were injected into rat striatum and their effects on dopamine, serotonin and their metabolites were examined at 1 h. Neuropeptide Y induced a dose-dependent increase in dopamine turnover in the ipsilateral striatum with no effect on serotonin turnover. When neuropeptide Y was coinjected with somatostatin there was an additive effect in increasing dopamine turnover. There was no alteration in striatal concentrations of gamma-aminobutyric acid, glutamate, or aspartate with either neuropeptide Y or somatostatin injections. These results suggest that neuropeptide Y may play a role with somatostatin in regulating striatal dopaminergic transmission.     

神经肽—Y在蛛网膜下腔出血引起脑血管痉挛中的作用

本实验采用大鼠经额向基底池Willis环处插管注入NPY,NE和5-HT,以γCBF变化为指标,观察它们对脑血管的在体效应。实验发现NPY对脑血管具有很强的收缩作用,以克分子浓度计算NPY引起脑血管收缩比5-HT强10倍,比NE强500倍,并可增加NE,5-HT的缩血管效应。人及大鼠CSF中NPY测定发现:SAH伴有CVS的病人,CSF中NPY达291.1±58pg/ml,与对照组(164±28.00pg/ml)相比,P<0.01;大鼠SAH后CSF中NPY含量从2.1±2.1增至6.0±3.2ng/ml(P<0.01),同时大鼠皮层内NPY含量从9.5±0.8下降至4.8±0.8ng/ml(P<0.01),提示脑神经元分泌的NPY参与了CVS过程,并在维持CVS持续状态方面起重要作用。实验还提示SAH病人CSF中NPY含量变化可以作为观察CVS是否出现的指标。     

Neuropeptide Y: Immunocytochemical localization to and effect upon feline pial arteries and veins in vitro and in situ

Plexuses of nerve fibres containing neuropeptide Y (NPY)-like immunoreactivity invest pial arteries belonging to the circle of Willis, pial arterioles, occasionally penetrating arterioles and large veins. A more sparse supply of NPY-like fibres are observed around pial veins and venules. The NPY-immunoreactive fibres are located within the adventitia or at the adventitia-media border. Only occasional fibres are present in cerebral vessels of animals in which the superior cervical ganglion has been removed one week previously. Administration of NPY resulted in strong, concentration-dependent contractions of isolated feline middle cerebral arteries whereas administration of avian pancreatic polypeptide (APP) elicited weak contractions. In chloraloseanaesthetized cats, perivascular microapplication of NPY in situ resulted in marked concentration-dependent contractions of cerebral pial arterioles (34.7±6.6%; maximum decrease in calibre with NPY. Perivascular administration of NPY resulted in the constriction of pial veins but the magnitude of the venous calibre reductions was smaller than the response of arterioles at each reductions was smaller than the response of arterioles at each concentration examined. APP did not elicit contraction of pial arterioles or veins during in situ conditions. The pharmacological and immunocytochemical results strongly indicate the existence of a novel perivascular neuronal system containing NPY, which mediates contraction of cerebral blood vessels and NPY is colocalized with NA in sympathetic nerves.     

The effect of splanchnic nerve stimulation and neuropeptide Y on cholera secretion and release of vasoactive intestinal polypeptide in the feline small intestine

The effect of sympathetic nerve stimulation and intra-arterial infusion of neuropeptide Y (NPY) on net fluid secretion and release of vasoactive intestinal polypeptide (VIP) was studied in the cat small intestine during a secretion due to cholera toxin. Activation of the splanchnic nerves (4 Hz, 5 ms, 5 V) decreased net fluid secretion to 57 +/- 10% of control. Concomitantly, the release of VIP was reduced to less than 50%. Furthermore, close i.a. infusion of NPY (estimated increase in plasma concentration 75 nmol l-1) reduced the net fluid secretion and VIP release to 27 +/- 5 and 28 +/- 4% of the pre-stimulatory value. The correlation between the decrease in net fluid secretion and reduction in VIP release showed a strong positive correlation (r = 0.83). These results strongly indicate that the antisecretory effect of sympathetic nerve stimulation during cholera diarrhoea is mediated by inhibition of secretory VIP neurons in the intestinal mucosa. A similar mechanism is also proposed for the intravascularly administered NPY.     

Some effects of the calcium promotor BAY K 8644 on feline cerebral arteries

The proposed calcium promotor BAY K 86(44) contracted feline basilar arteries partially depolarized by 10 mmol X 1(-1) potassium in a concentration-dependent manner (EC50 value: (2.1 +/- 1.2) X 10(-9) mol X 1(-1)). The concentration-response curve for prostaglandin (PG) F2 alpha was displaced to the left after pretreatment with BAY K 86(44). PGF2 alpha induced a biphasic contraction in calcium-free medium as has been described previously. The second PGF2 alpha-induced contraction phase in calcium-free medium was abolished by pretreatment with nifedipine or diltiazem. BAY K 86(44) restored the second phase in arteries pretreated with nifedipine, but not in vessels pretreated with diltiazem. The findings suggest that BAY K 86(44) acts as a promotor of calcium-influx, probably by interaction with the 'dihydropyridine receptor' in the cell membrane, and also provide support for the view that PGF2 alpha releases membrane-bound calcium.     

C-peptide potentiates the vasoconstrictor effect of neuropeptide Y in insulin-dependent diabetic patients

Recent findings suggest that proinsulin C-peptide improves renal and nerve function as well as microcirculation in patients with insulin-dependent diabetes possibly by stimulating Na-K+-ATPase activity. Furthermore, in vitro studies on proximal rat renal tubule cells show that the effect of C-peptide on Na+, K+-ATPase activity is potentiated in the presence of the vasoconstrictor peptide neuropeptide Y. The aim of the present study was to examine whether the effects of neuropeptide Y on resting forearm blood flow in insulin-dependent patients is altered in the presence of C-peptide. Forearm blood flow was measured by a plethysmographic method in eight insulin-dependent patients and six healthy control subjects. Neuropeptide Y (20, 200 and 2000 pmol min(-1)) was infused into the brachial artery before and during an i.v. infusion of C-peptide (5 pmol kg(-1) min(-1)). Basal blood flow was 36.7 +/- 2.2 mL min(-1) L(-1) tissue. It decreased in a dose dependent manner by 11 +/- 2, 18 +/- 3 and 25 +/- 3%, respectively, during infusion of neuropeptide Y. Administration of C-peptide increased basal blood flow by 25 +/- 6%, to 46.3 +/- 3.5 mL min(-1) L(-1) tissue (P < 0.01) and forearm glucose uptake by 76 +/- 34% (P < 0.05). Infusion of the three doses of neuropeptide Y during administration of C-peptide decreased forearm blood flow by 14 +/- 4, 22 +/- 3 and 42 +/- 4%. There was a significant difference (43%, P < 0.001) between the reduction in blood flow evoked by the high dose (2000 pmol min(-1)) of neuropeptide Y before and during C-peptide infusion. Similar differences were also obtained when data were calculated as changes in vascular resistance. C-peptide did not affect resting forearm blood flow or the response to neuropeptide Y in healthy controls. In conclusion, the present data demonstrate that C-peptide increases resting forearm blood flow and augments the vasoconstrictor effects of neuropeptide Y in insulin-dependent patients.     

环胞霉素A抑制神经肽Y诱导大鼠心肌细胞肥大效应

目的:观察Ca²⁺/CaM依赖的钙调神经磷酸酶(CaN)抑制剂环胞素A(CsA)对神经肽Y诱导心肌细胞肥大效应的影响。方法:用神经肽Y(NPY)刺激Wistar乳鼠心肌细胞,并用环胞素A加以干预。应用氚-亮氨酸([³H]-Leu)掺入法测定心肌细胞蛋白质合成速率、RT-PCR法测心肌细胞c-junmRNA表达。结果:(1)心肌细胞氚-亮氨酸([³H]-Leu)掺入量测定:与对照组相比,NPY10nmol/L组氚-亮氨酸([³H]-Leu)掺入量有所增高,但与对照组比无显著差别,而NPY100nmol/L组心肌细胞氚[³H]-Leu掺入量较对照组明显增高(P＜0.05)。CsA组和对照组相比无显著差别。(2)心肌细胞内c-junmRNA表达:NPY组心肌细胞c-junmRNA的RT-PCR产物量明显高于对照组和CsA组(P＜0.01),对照组和CsA组间无显著差别。结论:NPY刺激心肌细胞蛋白质合成增加、心肌细胞原癌基因(肥大早期反应基因)c-junmRNA表达,提示NPY可诱导心肌细胞肥大;CaN抑制剂CsA可阻断NPY上述效应,说明Ca²⁺/CaM依赖的CaN信号途径在其中起重要作用。     

红细胞裂解产物和血小板对离体动脉的收缩效应及其在脑血管痉挛中可能的作用

为探讨蛛网膜下腔出血(SAH)后晚期脑血管痉挛(CVS)的发病机理,本文测定了兔红细胞裂解产物(EBP)和血小板对牛离体基底动脉的收缩效应。结果表明,EBP和血小板均有强烈的缩血管效应;温育5～10天后EBP的效应减弱而血小板的效应则有所增强;加热100℃10分钟,EBP的缩血管效应消失,而血小板及对照5—HT、组胺和NE的效应均不减弱;血小板的缩血管效应能被酚(艹卡)明阻断,为阿斯匹林减弱;EBP能诱导血小板聚集,促进其TXA_2合成。这些结果提示:EBP和血小板在晚期CVS发病中都可能有重要作用;血小板的缩血管效应与血管活性胺和前列腺素类物质有关;EBP一方面可直接引起血管收缩,另一方面则可能通过激活血小板而加重CVS。     

Endothelium-independent potentiation by neuropeptide Y of vasoconstrictor responses in isolated arteries from rat and rabbit

An endothelium-dependent action of neuropeptide Y (NPY) has been implicated in studies on various vascular beds. In the present study, the requirement of an intact endothelium for NPY-evoked potentiation of the response to sympathetic nerve stimulation was determined in the small mesenteric arteries of the rat and in the central ear artery of the rabbit. Further, NPY-mediated inhibition of relaxing influences was determined in small mesenteric arteries of the rat. Vascular segments were mounted in a double myograph, where one of the two suspended vessels was denuded of endothelium by gently rubbing the intimal surface. Removal of endothelium was verified by en-face silver staining. In both species, the response to bursts of transmural field stimulation eliciting 10% of maximal contraction was potentiated 2-4 times in the presence of 10 nM NPY, whether the endothelium was present or not. In small mesenteric arteries precontracted with noradrenaline, addition of acetylcholine (I microM) caused relaxation only in vessels with an intact endothelium. Subsequent addition of 10 nM NPY enhanced vasoconstriction in both intact and endothelium-denuded vessels. The endothelium-independent beta-adrenergic agonist isoprenaline (I microM) relaxed both intact and denuded small mesenteric arteries, and in both further addition of 10 nM NPY increased the contraction to about the same extent. The results demonstrate that NPY potentiates the responses to sympathetic field stimulation in small mesenteric arteries from the rat and in central ear artery from rabbit whether the endothelium is present or not. NPY inhibits both endothelium-dependent and -independent relaxations in small mesenteric arteries from rat.     

Characterization of central actions of neuropeptide Y on food and water intake in rabbits

The effects of a 36-amino acid peptide, neuropeptide Y (NPY), on feeding and drinking behaviors were studied in young and adult rabbits. Intraventricular injection of NPY to adult rabbits induced feeding and drinking in a dose-related manner. While the lowest doses tested (0.2 micrograms) was without effect, other doses (0.5 and 1 microgram) elicited feeding and drinking almost instantaneously. When 1, 5 and 10 microgram doses were injected into young rabbits, immediate increases in feeding and drinking were evident, but differences in the magnitude of responses among these dosages were significant only in water consumption. Unlike studies in rats, in these rabbits NPY elicited a more pronounced response in drinking than in feeding. The drinking response after NPY administration was not a consequence of food intake because it occurred in the absence of food. With ad lib feeding, the majority of enhanced food consumption was confined to the first 30-min after NPY injection; however, an increased motivation to eat was retained for at least 2 hr after NPY when food was withheld and then returned. These observations are consistent with specific stimulatory effects of NPY on food and water intake.     

自发性高血压大鼠脑细小动脉神经肽Y分布的研究

为了解血管周围神经肽类分布与高血压时细小动脉构型重建之关系，我们采用自发性高血压大鼠（ＳＨＲ）软脑膜铺片技术，展示了血管网的各级分支，对血管系统进行了全面、立体的观察。并用免疫组织化学、图像分析仪对血管网上神经肽Ｙ（ＮＰＹ）分布进行定性定量分析。结果表明，ＳＨＲ大脑中动脉及其分支，小动脉、细动脉壁上含ＮＰＹ神经纤维分布表面积密度及ＮＰＹ抗体阳性反应物积分光密度均明显高于正常血压组（ＷＫＹ），这一实验结果揭示脑细小动脉含ＮＰＹ神经分布密度增加，使血管平滑肌营养调节作用增强，与其动脉收缩兴奋性增高，动脉平滑肌细胞肥大和高血压的发生发展有着明显关系。     

Pharmacological properties of prejunctional alpha-adrenoceptors in isolated feline middle cerebral arteries; comparison with the postjunctional alpha-adrenoceptors

In cat middle cerebral arteries (CMCA) preincubated with 3H-noradrenaline (NA), the outflow of tritium evoked by electrical stimulation was reduced to 32% by alpha-adrenoceptor (alpha-receptor) stimulation with oxymetazoline, and increased to 487% by alpha-receptor blockade with HEAT. The relative order of potency for alpha-receptor agonists on prejunctional receptors was: clonidine greater than or equal to oxymetazoline greater than phenylephrine, and the antagonist rauwolscine was more potent than prazosin. This indicates that the prejunctional alpha-receptors are mainly of alpha 2-type. Rauwolscine was more potent than prazosin in inhibiting the contractions induced by NA, indicating a predominance of alpha 2-receptors postjunctionally. Apart from clonidine having higher intrinsic activity pre- than postjunctionally, all drugs examined (oxymetazoline, phenylephrine, rauwolscine, HEAT (BE2254), and prazosin) had similar concentration-effect curves on the pre- and postjunctional receptors. Furthermore, the ratios of EC50-values pre- and postjunctionally of rauwolscine, oxymetazoline, and clonidine were all close to unity. These results indicate that pre- and postjunctional alpha 2-receptors in the CMCA have similar pharmacological characteristics and cannot be influenced separately by the presently used drugs.     

Sympathetic neurogenic Ca2+ signalling in rat arteries: ATP, noradrenaline and neuropeptide Y

The sympathetic nervous system (SNS) plays an essential role in the control of total peripheral vascular resistance by controlling the contraction of small arteries. The SNS also exerts long-term trophic influences in health and disease; SNS hyperactivity accompanies most forms of human essential hypertension, obesity and heart failure. At their junctions with smooth muscle cells, the peri-arterial sympathetic nerves release ATP, noradrenaline (NA) and neuropeptide Y (NPY) onto smooth muscle cells. Confocal Ca²⁺ imaging studies reveal that ATP and NA each produce unique types of postjunctional Ca²⁺ signals and consequent smooth muscle cell contractions. Neurally released ATP activates postjunctional P2X₁ receptors to produce local, non-propagating Ca²⁺ transients, termed 'junctional Ca²⁺ transients', or 'jCaTs'. Neurally released NA binds to α₁-adrenoceptors and can activate Ca²⁺ waves or more uniform global changes in [Ca²⁺]. Neurally released NPY does not appear to produce Ca²⁺ transients directly, but significantly modulates NA-induced Ca²⁺ signalling. The neural release of ATP and NA, as judged by postjunctional Ca²⁺ signals, electrical recording of excitatory junction potentials and carbon fibre amperometry to measure NA, varies markedly with the pattern of nerve activity. This probably reflects both pre- and postjunctional mechanisms, which are not yet fully understood. These phenomena, together with different temporal patterns of sympathetic nerve activity in different regional circulations, are probably an important mechanistic basis of the important selective regulation of regional vascular resistance and blood flow by the sympathetic nervous system.     

Co-existence of neuropeptides and differential inhibition of vasodilator responses by neuropeptide Y in guinea pig uterine arteries

The co-localization of substance P (SP) with calcitonin gene-related peptide (CGRP), and vasoactive intestinal peptide (VIP) with neuropeptide Y (NPY) of the guinea pig uterine artery were investigated with immunocytochemistry. The SP/CGRP fibre population was distinct from the VIP/NPY fibre population. Both types of fibres ran in the medial-adventitial border, and appeared as coarsed and fine varicosed. Uterine arterial dilatation was evoked by acetylcholine (ACh), SP, CGRP, and VIP in precontracted arteries as examined by a sensitive in vitro method. Strong relaxations were seen by ACh, CGRP and VIP. NPY had no relaxant effect per se but was found to be a potent inhibitor of vasodilation induced by ACh and SP, while relaxations induced by VIP and CGRP were unaffected. The functional significance of NPY in the uterine artery may to a large extent be to increase tension not only by potentiation of contraction but additionally by inhibiting vasodilator responses.     

Renal effects of neuropeptide Y

 Neuropeptide Y (NPY) is a co-transmitter of the sympathetic nervous system including the renal nerves. The kidney expresses NPY receptors, which can also be activated by peptide YY (PYY), a circulating hormone released from gastrointestinal cells. Five subtypes of NPY receptors have been cloned, among which Y₁, Y₂ and Y₅ appear to be involved in the regulation of renal function. NPY produces potent renal vasoconstriction in vitro in isolated interlobar arteries and in the isolated perfused kidney and in vivo upon intrarenal or systemic administration via a Y₁ receptor. Nevertheless glomerular filtration rate is altered only little if at all by NPY, indicating a greater effect on the vas efferens than the vas afferens. NPY can inhibit renin release via Y₁-like receptors. NPY can stimulate Na⁺/K⁺ adenosine triphosphatase (Na⁺/K⁺-ATPase) in proximal tubules via Y₂ receptors and can antagonize the effects of vasopressin on isolated collecting ducts. It can also act prejunctionally to inhibit noradrenaline release via Y₂ receptors. Despite the profound reductions of renal blood flow, systemic NPY infusion can cause diuresis and natriuresis; this is largely independent of pressure natriuresis mechanisms and is possibly mediated by an extrarenal Y₅ receptor. Studies with the converting enzyme inhibitor ramiprilat and the bradykinin receptor antagonist icatibant indicate that bradykinin mediates, at least partly, diuretic NPY effects. NPY antagonists enhance basal renal blood flow but do not alter basal diuresis or natriuresis indicating that renovascular, but not tubular, NPY receptors may be tonically activated by endogenous NPY.