NPY-induced Contractions Research Articles

Marked neuropeptide Y-induced contractions via NPY-Y 1 receptor and its desensitization in rat veins

The aim of this study was to investigate neuropeptide Y (NPY)-induced vasoconstrictions in rat blood vessels and which NPY receptor subtype is involved in vasoconstrictions. NPY produced marked contractions in rat common jugular, brachial, portal, femoral and tail veins, and vena cava inferior, whereas it produced little or no contractions in rat common carotid, brachial, femoral and tail arteries, and thoracic and abdominal aortae. The maximal NPY-induced contractions were larger than maximal phenylephrine (PE)-induced contractions in the veins. These NPY-induced contractions were blocked by the Y 1 antagonists, SRL-21, and BIBP3226 but not by the Y 5 antagonist, L-152804. A Y 2 agonist, NPY (13–36), did not produce contractions. RT-PCR showed that NPY-Y 1 was the only receptor subtype in the veins indicating that NPY-induced contractions are mediated through the Y 1 receptor. Pretreatment with NPY showed a rapid and long-lasting desensitization of these contractions. The marked NPY-induced contractions and its desensitization in the veins suggest the physiological relevance of NPY in the venous circulation.

Characterization of NPY receptors mediating contraction in rat intramyocardial coronary arteries

In vitro experiments in a microvascular myograph were designed in order to characterize the receptor subtypes and the mechanisms underlying the contractions induced by neuropeptide Y (NPY) in rat coronary small arteries. The rank order of potency for NPY-receptor agonist-induced increases in tension in endothelium-intact preparations was polypeptide Y (PYY)>NPY≥[Leu 31Pro 34]NPY, while NPY 13–36 only induced small contractions at the highest concentration applied. The selective neuropeptide Y 1 receptor antagonist, BIBP 3226, caused rightward shifts in the concentration–response curves for NPY and the slope of the Schild plot was not significantly different from unity. The p A 2 value for BIBP 3226 against NPY was 7.88±0.15 ( n=6). We have earlier shown that endothelial cell removal does not change the contractile responses induced by NPY, but indomethacin (3×10 −6 M) significantly reduced the contractions induced by the peptide. In contrast, the thromboxane receptor antagonist, SQ29548, which abolished the contractions induced by the thromboxane analogue, U46619, did not change the concentration–response curves for NPY. In conclusion, the present study suggests that Y 1 receptors mediate NPY-induced contractions in rat coronary resistance arteries, and that a non-thromboxane prostanoid is involved in the contractile mechanism.

Characterization of neuropeptide Y receptors mediating contraction, potentiation and inhibition of relaxation.

In addition to its direct vasoconstrictive effect, neuropeptide Y (NPY) potentiates noradrenaline-(NA) induced contraction and inhibits acetylcholine-(ACh) induced relaxation: The aim of the present study was to elucidate the NPY receptor subtypes responsible for mediating these three responses. NPY, peptide YY (PYY) and pro34NPY (a NPY Y1 receptor agonist) induced equipotent and equally strong concentration-dependent contractions of guinea pig basilar arteries. NPY13-36 (a NPY Y2 receptor agonist), however, caused only weak contraction with significantly lower potency. The NPY-induced contraction was significantly inhibited by the selective NPY Y1 receptor antagonist BIBP3226 (1 microM). NPY, PYY and pro34NPY but not NPY13-36 significantly potentiated the NA-induced contraction in guinea pig mesenteric arteries. The potentiation was significantly inhibited by BIBP3226 (1 microM). In precontracted guinea pig basilar arteries, ACh induced a concentration-dependent relaxation which was significantly inhibited by NPY, PYY and NPY13-36 but not by pro34NPY. BIBP3226 had no significant effect on the NPY-induced inhibition of the relaxation. These results suggests that the NPY Y1 receptors mediate the direct contraction and the potentiation of the NA-induced contraction but not the inhibition of the ACh-induced relaxation. This effect seems to be mediated by another NPY receptor subtype, presumably by the Y2 receptor, as judged from the agonist potency order.

Characterization of neuropeptide Y (NPY) receptors in human cerebral arteries with selective agonists and the new Y1 antagonist BIBP 3226

1. We have characterized pharmacologically the receptor subtype(s) responsible for the neuropeptide Y (NPY)-induced vasoconstriction in human cerebral arteries. NPY, PYY and several of their derivatives with well defined affinities at the known Y1 and Y2 receptor subtypes were used. Moreover, we tested the ability of the new Y1 receptor antagonist, BIBP 3226, to antagonize the NPY-induced cerebral vasoconstriction. 2. NPY, PYY and their agonists with high affinities at the Y1 receptor subtype ([Leu31-Pro34]-NPY and [Leu31-Pro34]-PYY) elicited strong, long lasting and concentration-dependent contractions of human cerebral arteries. Compounds with Y2 affinity such as PYY3-36 or NPY13-36 either elicited a submaximal contraction at high concentrations or failed to induce any significant vasomotor response. Also, the application of NPY or the specific Y1 agonist, [Leu31-Pro34]-NPY, to human cerebral vessels pretreated with the Y1 agonist, NPY13-36, resulted in contractile responses identical to those obtained when these compounds were tested without prior application of NPY13-36. 3. The order of agonist potency at the human cerebrovascular receptor was: [Leu31-Pro34]-NPY = [Leu31-Pro34]-PYY > or = NPY > PYY > PYY3-36 > > > NPY13-36, which corresponded to that reported previously at the neuronal and vascular Y1 receptors. 4. Increasing concentrations (10(-9)-10(-6) M) of the Y1 receptor antagonist, BIBP 3226, to human cerebral vessels caused a parallel and rightward shift in the NPY dose-response curves without any significant change in the maximal contractile response. The calculated pA2 was 8.52 +/- 0.13, a value compatible with the reported affinity at the rodent and human Y1 receptor. 5. We conclude that Y1 receptors exclusively, mediate the NPY-induced contraction in human cerebral arteries and we show that BIBP 3226 is a potent and competitive antagonist of this YI-mediated vasoconstriction.

Prejunctional alpha-2 adrenoceptors and K + channel blockers in rat vas deferens

A parallel increase in systemic plasma levels of neuropeptide Y (NPY)-like immunoreactivity (LI) and noradrenaline (NA) was found during thoracotomy and surgery involving cardiopulmonary bypass in man. Thus, plasma levels of NPY-LI increased from 29 ± 4 pmol/l before anaesthesia to 59 ± 10 after thoracotomy and to 87 ± 8 pmol/l upon cardiopulmonary bypass. The corresponding NA levels increased from 1.3 ± 0.1 nmol/l before anaesthesia to 3.0 ± 0.6 and 4.2 ± 5 nmol/l after thoracotomy and cardiopulmonary bypass, respectively. A significant correlation was found between plasma levels of NPY-LI and NA during the operation but not between NPY-LI and adrenaline. The NPY-LI in human plasma was found to be similar to synthetic porcine NPY on reversed phase high performance liquid chromatography. Human submandibular arteries contained high levels of NPY-LI (24 ± 3 pmol/g). In in vitro experiments on isolated human submandibular arteries, NPY in low concentrations (1000 pmol/l) was found to potentiate the contractile effects of NA or transmural nerve stimulation and to exert vasoconstrictor activity per se in higher concentrations. The calcium-entry antagonist nifedipine abolished both the NPY-induced contractions and the enhancement of NA-evoked contractions. NPY depressed the nerve stimulation-evoked 3H-NA release from human submandibular arteries via a prejunctional mechanism which was resistant to nifedipine. NPY contracted human mesenteric veins and renal arteries, but not mesenteric arteries. In conclusion, NPY seems to be co-released with NA upon sympathetic activation in man. Furthermore, NPY exerts both pre- and postjunctional effects on sympathetic control of human blood vessels.

Interactions between NPY and its receptor: assessment using anti-NPY antibodies

The present data show that monoclonal antibodies (NPY02, NPY03, NPY04, NPY05) directed against 4 distinct epitopes on NPY may have different actions on NPY binding and NPY-induced cellular responses. NPY02 and NPY05 recognize the 11–24 and 32–36 amidated form of NPY, respectively. These 2 antibodies block the binding of NPY to its receptor as well as the NPY-induced inhibition of cAMP accumulation caused in SK-N-MC cells by forskolin. NPY02 and NPY05 have also an inhibitory action on NPY-induced contraction of rabbit femoral arteries. NPY03 and NPY04 are directed against the 27–34 and 1–12 part of NPY, respectively. NPY03 and NPY04 inhibit the binding of NPY only at very high concentrations and have a weak effect on cAMP response to NPY. NPY02 and NPY05 might provide useful tools to study the effect of NPY in cellular systems and organ preparations.

α-trinositol blocks neuropeptide Y-induced inositolphosphate formation in cerebral vessels

Neuropeptide Y (NPY) induces contraction of guinea-pig basilar arteries via activation of Y 1 receptors. This contraction is blocked by D-myo-inositol-1,2,6-triphosphate (α-trinositol). Previous binding studies have shown that α-trinositol has no effect at Y 1 or Y 2 binding sites thus the antagonistic effect should occur at the level of a second messenger. We have examined the effects of NPY on the formation of inositol phosphates (IP) and have looked for an antagonistic effect of α-trinositol. NPY (10 −9 −3 × 10 −7 M) induced strong concentration-dependent contraction of basilar arteries from young guinea-pigs (weight 200–250 g) (E max: 76.4 ± 11.1%) but not of arteries from old guinea-pigs (weight > 500 g) (E max: 2.8 ± 1.5%). [Pro 34]NPY and PYY induced contraction of similar magnitude and potency, whereas NPY 13–36 had only a weak effect. This demonstrates an effect via the Y 1 type of NPY receptor. The contraction induced by NPY was blocked by α-trinositol (p < 0.05). LiCl (2 × 10 −4M), used to inhibit IP breakdown, had no effect on the contraction induced by NPY. NPY (10 −10 – 10 −8M) increased the formation of IP in cerebral vessels from young guinea-pigs from 357 ± 48 cpm/mg w.w. to 900 ± 233 cpm/mg w.w. However, there was no alteration in IP formation in cerebral vessels from old guinea-pigs (NPY 10 −9 – 10 −7M). In the presence of α-trinositol (10 −8 – 10 −6M) the NPY induced stimulation of IP formation was totally abolished. α-trinositol at a concentration of 10 −8M but not 10 −7M and 10 −6M significantly increased the formation of IP. Fractionation of the total IP into IP 3, IP 2 and IP 1 showed mainly increased values which were totally abolished by α-trinositol. It is concluded that α-trinositol antagonizes NPY-induced contraction via mechanisms that regulate the intracellular IP formation including IP 3 and IP 2. This may occur via modulation of PIP 2 breakdown by antagonizing phospholipase C activation. Interestingly, the effect seems to be directed selectively towards NPY mediated effects.

Contractile response to neuropeptide Y of rat isolated duodenum

The response of isolated duodenum to neuropeptide Y (NPY) was studied isotonically in neonatal and adult rats. Neuropeptide Y (10 −8 to 10 −6 M) elicited a biphasic contraction of isolated duodenum from neonatal rats, but monophasic and weak contraction of adult duodenum. The first phase of NPY-induced contraction of neonatal duodenum was concentration dependent and partially inhibited by preincubation with tetrodotoxin, a Na + channel blocker, hyoscine, a muscarinic antagonist, suramin, a P 2 purinoceptor antagonist, and indomethacin, an inhibitor for prostaglandin biosynthesis. Neuropeptide Y(13–36), a specific Y 2 NPY receptor agonist, elicited a concentration-dependent contraction of neonatal rat duodenum. The duodenal response to NPY thus changes during development in rats. Both cholinergic and purinergic transmission and prostaglandin biosynthesis may be involved in the NPY-induced contraction of neonatal duodenum. Neuropeptide Y-induced contraction may be mediated through presynaptic Y 2 receptors.

Regional heterogeneity in the contractile and potentiating effects of neuropeptide Y in rat isolated coronary arteries: modulatory action of the endothelium.

1. Neuropeptide Y (NPY) induced a concentration-dependent contraction of isolated rings of proximal epicardial (PC) and distal intramural (DC) coronary arteries of the rat, with an EC50 of ca. 1 x 10(-7) M. The NPY-induced contraction at 3 x 10(-7) M was significantly smaller in PC than DC arteries: 34% vs. 55% of the 125 mM K(+)-induced response, respectively. 2. NPY (2 x 10(-8) M) increased the sensitivity to noradrenaline (NA) and 5-hydroxytryptamine (5-HT) more in PC (4.2 and 2.8 fold, respectively) than in DC arteries (2.2 and 1.4 fold, respectively). The maximal contractile response to NA and 5-HT was increased more in DC (43% and 29%, respectively) than in PC arteries (20% and 12%, respectively). 3. Removal of the endothelium increased the sensitivity and maximal response to NPY as well as the spontaneous myogenic tone in PC but not in DC arteries. NPY had no relaxing effect on PC and DC arteries submaximally contracted with 10(-6) M prostaglandin F2 alpha, suggesting that spontaneous rather than stimulated release of endothelium-derived relaxing factor (EDRF) depresses the contractile action of NPY in PC arteries. 4. The results indicate a heterogeneity in the contractile and potentiating action of NPY in rat coronary arteries depending on size or location in the coronary circulation.

Neuropeptide Y antagonistic properties of D-myo-inositol-1.2.6-trisphosphate in guinea pig basilar arteries

The antagonistic properties on neuropeptide Y (NPY)-induced contraction of the guinea pig basilar artery of D-myo-inositol-1.2.6-triphosphate (PP56) has been examined using a sensitive in vitro system. It was observed that PP56 did not per se cause contraction or relaxation of precontracted vessel segments. However, it was found to be a non-competitive antagonist of NPY-induced contraction. This effect was observed in the concentration range 10 −8–10 −6 M PP56. A slight potentiation of endothelin I-induced contraction was seen at high concentrations (10 −3M). In contrast there was no modulation of the contractile effects elicited by bradykinin, noradrenaline, 5-hydroxytryptamine (5-HT) or prostaglandin F 2α (PGF 2α) apart from a slight reduction in maximum effect at 10 −4M and 10 −3 M PP56. PP56 was observed to possess antihistaminic and anticholinergic properties in the concentration range 10 −5 M–10 −3 M. The relaxant effects of vasoactive intestinal peptide, calcitonin gene-related peptide, neurokinin A and substance P were only modified to a minor extent by PP56 in concentrations of 10 −4 M and 10 −3 M. In conclusion, PP56 appears to be the first non-peptide which potently and rather selectively antagonizes NPY-induced contractions of the guinea pig basilar artery. In high concentrations, PP56 may modify the responses of other agents tested, including histamine and acetylcholine.

Evidence that neuropeptide Y released from noradrenergic axons causes prolonged contraction of the guinea-pig uterine artery

The participation of neuropeptide Y (NPY) in transmission from sympathetic vasoconstrictor neurons was investigated in the guinea-pig uterine artery, where NPY has been demonstrated immunohistochemically in noradrenergic axons. Exogenous NPY produced long-lasting contractions of isolated arterial segments at low resting tone. Low concentrations of NPY (10 −8−3 × 10 −7 mol · l −1) were more potent than equimolar concentrations of noradrenaline (NA). NPY produced concentration-dependent desensitization to further application of NPY, but did not affect the magnitude of NA contractions. Trypsin (1.4–2 μg · ml −1) reduced NPY-induced contractions by 80–100%, but did not alter NA-induced contractions. Transmural electrical stimulation of arterial segments, after surgical removal of vasodilator axons, produced biphasic contractions which were abolished by guanethidine. Prazosin abolished the fast phase of the neurogenic contraction, leaving a slow contraction with a time course similar to that produced by a low concentration of NPY. The slow contraction was more pronounced at higher frequencies of stimulation (15–20 Hz) than at lower frequencies, and was selectively reduced after desensitization produced by NPY (10 −5 mol · l −1), or after exposure to trypsin. These results suggest that sympathetic vasoconstriction of the guinea-pig uterine artery is produced by release of both NA and NPY from noradrenergic axons.

Actions of calcium antagonists on pre- and postjunctional effects of neuropeptide Y on human peripheral blood vessels in vitro

The mechanisms underlying the contractile effects of neuropeptide Y (NPY) in relation to those of noradrenaline (NA) on small human blood vessels were studied in vitro. NPY caused contractions of mesenteric veins, renal and skeletal muscle arteries but not of mesenteric arteries. NPY was about 5- to 10-fold more potent than NA. The maximal contractile responses to NPY (5×10 −7 M) were 38 ± 4, 37 ± 8 and 95 ± 16% of the response evoked by NA 10 −5 M in the mesenteric vein, renal and skeletal muscle arteries respectively. The NPY effects were resistant to adrenoceptor antagonists. The calcium antagonist nifedipine reduced the effect of NA but not the contractile response to NPY on mesenteric veins. Nidefipine and felodipine reduced the contractile response to both NA and NPY on renal and skeletal muscle arteries. In contrast to the contractile effects of K +, the responses to NPY and NA were largely uninfluenced by changes in extracellular Ca 2+ concentrations. Nifedipine still inhibited the NPY contractions in a Ca 2+-free medium while high extracellular Ca 2+ (7.5 mM) partly reduced the nifedipine effect. NPY reduced the nerve stimulation-evoked [ 3H]NA overflow from the mesenteric veins via a nifedipine resistant mechanism. The stable analogue α,β-methylene adenosine triphosphate (mATP) was more potent than ATP and had nifedipine-sensitive contractile effects similar to those of NA on the human blood vessels without influencing the nerve-evoked [ 3H]NA efflux. In conclusion, NPY exerts a potent nifedipine-sensitive vasoconstrictor activity, especially on human skeletal muscle arteries in vitro, although the influx of extracellular calcium may not be a crucial mechanism. The NPY-induced contractions of mesenteric veins and the inhibition of nerve-evoked [ 3H]NA efflux seem to be mediated via nifedipine resistant messenger systems.

Neuropeptide Y and sympathetic vascular control in man

A parallel increase in systemic plasma levels of neuropeptide Y (NPY)-like immunoreactivity (LI) and noradrenaline (NA) was found during thoracotomy and surgery involving cardiopulmonary bypass in man. Thus, plasma levels of NPY-LI increased from 29 ± 4 pmol/l before anaesthesia to 59 ± 10 after thoracotomy and to 87 ± 8 pmol/l upon cardiopulmonary bypass. The corresponding NA levels increased from 1.3 ± 0.1 nmol/l before anaesthesia to 3.0 ± 0.6 and 4.2 ± 5 nmol/l after thoracotomy and cardiopulmonary bypass, respectively. A significant correlation was found between plasma levels of NPY-LI and NA during the operation but not between NPY-LI and adrenaline. The NPY-LI in human plasma was found to be similar to synthetic porcine NPY on reversed phase high performance liquid chromatography. Human submandibular arteries contained high levels of NPY-LI ( 24 ± 3 pmol/g ). In in vitro experiments on isolated human submandibular arteries, NPY in low concentrations (1000 pmol/l) was found to potentiate the contractile effects of NA or transmural nerve stimulation and to exert vasoconstrictor activity per se in higher concentrations. The calcium-entry antagonist nifedipine abolished both the NPY-induced contractions and the enhancement of NA-evoked contractions. NPY depressed the nerve stimulation-evoked 3H-NA release from human submandibular arteries via a prejunctional mechanism which was resistant to nifedipine. NPY contracted human mesenteric veins and renal arteries, but not mesenteric arteries. In conclusion, NPY seems to be co-released with NA upon sympathetic activation in man. Furthermore, NPY exerts both pre- and postjunctional effects on sympathetic control of human blood vessels.

Characterization of the contractile effect of neuropeptide Y in feline cerebral arteries.

The action of neuropeptide Y (NPY), which coexists with noradrenaline (NA) in perivascular sympathetic nerves, has been examined on feline cerebrovascular smooth muscle using a sensitive in vitro system. The direct cerebrovascular responses of peptides with structural similarities with NPY, peptide YY (PYY), avian (APP), and bovine (BPP) and human (HPP) pancreatic polypeptides, have been compared with that of NPY on isolated feline cerebral arteries. The relative potency for contractions induced by the peptides is: NPY, PYY greater than APP greater than BPP, HPP. The alpha-adrenoceptor antagonist rauwolscine, which blocked the response to noradrenaline (NA), had no effect on NPY-induced contractions. Neuropeptide Y significantly potentiated contractions induced by 10(-6) M NA, but not by 10(-5) M. Withdrawal of Ca2+ from the extracellular medium for 30 min reduced the contractile response to NPY in cerebral vessels by about 80%. Subsequent readdition of Ca2+ caused reproducible contractions which were inhibited by the calcium entry blocker nimodipine. Nimodipine also relaxed isolated middle cerebral artery segments contracted by NPY and NA in a concentration-dependent manner. The data suggest that NPY mediates contraction of cerebrovascular smooth muscle via a mechanism that is dependent on the concentration of extracellular calcium.

Neuropeptide Y: Cerebrovascular innervation an vasomotor effects in the cat

Avian pancreatic polypeptide (APP) has been proposed to be a neurotransmitter in a subpopulation of sympathetic nerves. Here, we present immunocytochemical and pharmacological evidence that the structurally related peptide, neuropeptide Y (NPY), is likely to be the biologically active material in these nerves. Cerebral arteries from cats are invested with a dense network of NPY-containing nerve fibres, as demonstrated by immunocytochemistry. This immunoreaction is abolished by prior removal of the superior cervical ganglion. NPY causes strong contractions of cerebral arteries in vitro whereas APP has small effects on the vasomotor reactivity. The NPY-induced contractions were not inhibited by the α 2-adrenoceptor antagonist rauwolscine (10 −7 M) or the 5-hydroxytryptamine antagonist ketanserin (10 −7 M). The contractions were, however, sensitive to calcium removal or to the calcium antagonist diltiazem (10 −4 M).