Effects of vasoactive neuropeptides on human saphenous vein

Altered post-capillary and collecting venular reactivity in skeletal muscle with metabolic syndrome

KEY POINTS

With the development of the metabolic syndrome, both post-capillary and collecting venular dilator reactivity within the skeletal muscle of obese Zucker rats (OZR) is impaired. The impaired dilator reactivity in OZR reflects a loss in venular nitric oxide and PGI₂ bioavailability, associated with the chronic elevation in oxidant stress. Additionally, with the impaired dilator responses, a modest increase in adrenergic constriction combined with an elevated thromboxane A₂ production may contribute to impaired functional dilator and hyperaemic responses at the venular level. For the shift in skeletal muscle venular function with development of the metabolic syndrome, issues such as aggregate microvascular perfusion resistance, mass transport and exchange within with capillary networks, and fluid handling across the microcirculation are compelling avenues for future investigation.

ABSTRACT

While research into vascular outcomes of the metabolic syndrome has focused on arterial/arteriolar and capillary levels, investigation into venular function and how this impacts responses has received little attention. Using the in situ cremaster muscle of obese Zucker rats (OZR; with lean Zucker rats (LZR) as controls), we determined indices of venular function. At ∼17 weeks of age, skeletal muscle post-capillary venular density was reduced by ∼20% in LZR vs. OZR, although there was no evidence of remodelling of the venular wall. Venular tone at ∼25 μm (post-capillary) and ∼75 μm (collecting) diameter was elevated in OZR vs. LZR. Venular dilatation to acetylcholine was blunted in OZR vs. LZR due to increased oxidant stress-based loss of nitric oxide bioavailability (post-capillary) and increased α₁ - (and α₂ -) mediated constrictor tone (collecting). Venular constrictor responses in OZR were comparable to LZR for most stimuli, although constriction to α₁ -adrenoreceptor stimulation was elevated. In response to field stimulation of the cremaster muscle (0.5, 1, 3 Hz), venular dilator and hyperaemic responses to lower frequencies were blunted in OZR, but responses at 3 Hz were similar between strains. Venous production of TxA₂ was higher in OZR than LZR and significantly higher than PGI₂ production in either following arachidonic acid challenge. These results suggest that multi-faceted alterations to skeletal muscle venular function in OZR may contribute to alterations in upstream capillary pressure profiles and the transcapillary exchange of solutes and water under conditions of metabolic syndrome.

The role of endothelin-1 in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare but debilitating disease, which if left untreated rapidly progresses to right ventricular failure and eventually death. In the quest to understand the pathogenesis of this disease differences in the profile, expression and action of vasoactive substances released by the endothelium have been identified in patients with PAH. Of these, endothelin-1 (ET-1) is of particular interest since it is known to be an extremely powerful vasoconstrictor and also involved in vascular remodelling. Identification of ET-1 as a target for pharmacological intervention has lead to the discovery of a number of compounds that can block the receptors via which ET-1 mediates its effects. This review sets out the evidence in support of a role for ET-1 in the onset and progression of the disease and reviews the data from the various clinical trials of ET-1 receptor antagonists for the treatment of PAH.

The cardiovascular system and the biochemistry of grafts used in heart surgery

Blood is pumped into the cardiac muscle through arteries called the coronary arteries. Over time, the accumulation of cholesterol, coagulation factors, and cells on the walls of these arteries causes the walls to thicken and lose their elasticity, resulting in the development of atherosclerosis. When the blood supply of the heart is diminished by atherosclerosis, it can be restored by bypass surgery, in which atherosclerosis-free vein and/or artery grafts taken from another area of the body are used to replace the atherosclerotic vessels. These biological grafts used in surgery differ in biochemical composition and long-term patency. Although the great saphenous vein (GSV) has been the most popular graft material in revascularization for years, it has recently been superseded by the internal mammarian artery (IMA), which has a lower incidence of recurrence of atherosclerosis. The aim of the present review is briefly to address the structure of the cardiovascular system and blood vessels, and then, in the light recent data, to present the biochemical compositions and individual advantages of the graft materials used to restore an impaired blood supply to the heart.

Effect of substance P on venous tone in conscious rats

Substance P is an undecapeptide that belongs to the mammalian tachykinin family. We investigated the effects of substance P on venous tone in conscious rats through measurement of mean circulatory filling pressure. The effects of substance P (10 and 30 nmol/kg, IV) and the vehicle (0.9% NaCl) on mean arterial pressure, heart rate, and mean circulatory filling pressure were examined in 2 groups each of conscious rats: rats without or with ganglionic blockade through pretreatment with mecamylamine (10 mg/kg, IV) and norepinephrine (4 microg/kg/min, IV). In the unblocked rats, both doses of substance P reduced mean arterial pressure (-19 +/- 1 and -35 +/- 2 mm Hg) and increased heart rate (+113 +/- 14 and +115 +/- 23 beats/min). The high dose of substance P also decreased mean circulatory filling pressure (-1.7 +/- 0.3 mm Hg). In the ganglionic-blocked rats, both doses of substance P decreased mean arterial pressure (-48 +/- 6 and -73 +/- 6 mm Hg) and mean circulatory filling pressure (-2.9 +/- 0.4 and -4.2 +/- 0.8 mm Hg) but did not affect HR. In conclusion, substance P is a vasodilator peptide that has a prominent venodilator action.

Somatostatin-induced gastric protection against ethanol: involvement of nitric oxide and effects on gastric mucosal blood flow

BACKGROUND/AIMS

The mechanisms of somatostatin-mediated gastroprotection are not fully understood. Aims of this study were to determine in the rat the role of nitric oxide (NO) in somatostatin-induced effects on gastric mucosal protection and blood flow (GMBF) in the absence and in the presence of intraluminal ethanol.

METHODS

Ethanol (70% v/v)-induced gastric mucosal injury after orogastric dosing was quantitated at 30 min and GMBF determined in an ex vivo gastric chamber preparation.

RESULTS

Somatostatin (4 microg/kg; i.p.) protection against ethanol-induced ulceration was prevented by the NO inhibitor L-NNA and restored by L-arginine, but not D-arginine. Somatostatin (1-8 microg/kg; i.p.) did not effect basal GMBF. The gastroprotective dose of somatostatin (4 microg/kg; i.p.) prevented the decrease in GMBF caused by ethanol. L-NNA reversed this vascular effect of somatostatin.

CONCLUSION

Somatostatin-induced gastroprotection and restoration of GMBF during ethanol exposure involve mechanisms which are dependent on NO generation.

Effect of somatostatin on rabbit isolated coronary arteries

Somatostatin analogues are capable of inhibiting vascular smooth muscle and endothelial cell proliferation. However, little is known about the effect of somatostatin on vascular responses in endothelium-denuded coronary arteries in vitro. The aim of this work was to determine whether or not somatostatin prevented the contractile response induced by 5-hydroxytryptamine and acetylcholine in endothelium-denuded rabbit coronary arteries. Somatostatin attenuated the contraction produced by 5-hydroxytryptamine in both proximal (PC) and distal coronary (DC) arteries (contraction induced by 10(-4) M 5-hydroxytryptamine was inhibited by 10(-6) M somatostatin by 90.8 +/- 11.0% (P < 0.001, n = 9) and by 46.2 +/- 14.0% (P < 0.05, n = 9) in DC and PC, respectively), but concentration-dependently decreased the contraction induced by U46619 (11alpha-epoxy-methanoprostaglandin F2alpha) only in PC arteries, suggesting that the response of PC and DC arteries to somatostatin were qualitatively different. Furthermore, we suggest that somatostatin may enhance acetylcholine-induced relaxation by combination of increasing endothelium-dependent relaxation (by a NO-dependent mechanism) and blocking contraction at the muscle level.

Octreotide potentiates PKC-dependent vasoconstrictors in portal-hypertensive and control rats

BACKGROUND & AIMS

The effect of octreotide on vascular tone in the superior mesenteric artery (SMA) was studied in portal-hypertensive (portal vein-ligated) and sham-operated rats.

METHODS

In vitro-perfused SMA vascular beds were tested for the cumulative dose-response to octreotide at baseline conditions and after preconstriction with different vasoconstrictors (alpha1-agonist methoxamine, endothelin [ET-1], phorbol ester [PdBu], and potassium chloride [KCl]).

RESULTS

Octreotide did not affect baseline perfusion pressures (without preconstriction). alpha1-Adrenergic-, ET-1-, and PdBu-, but not KCl-, induced vasoconstriction was significantly potentiated by octreotide. This effect was dose-dependent and not different in portal vein-ligated and sham rats. Amplification of alpha1-adrenergic vasoconstriction by octreotide was significantly enhanced by nitric oxide inhibition (N(W)-nitro-L-arginine, 10(-4) mol/L) as well as by removal of the endothelium, and was completely suppressed by inhibition of protein kinase C (calphostin C, 1 micromol/L), phospholipase A2 (quinacrine, 5 micromol/L), and cyclooxygenase (indomethacin, 20 micromol/L).

CONCLUSIONS

Not directly, but in the presence of vasoconstrictors involving activation of protein kinase C, octreotide exerts a local vasoconstrictive effect on vascular smooth muscle of SMA. This potentiation is equipotent in portal vein-ligated and sham rats, immediate in onset, and mediated via phospholipase A2 and cyclooxygenase-derived prostanoids. This indicates that in preprandial conditions octreotide enhances the vasoconstrictive effect of dependent vasoconstrictors.

Somatostatin receptor subtype expression and function in human vascular tissue

In animal models the somatostatin analog angiopeptin inhibits intimal hyperplasia by acting primarily through somatostatin receptor 2 (SSTR-2). However, the results of clinical trials using angiopeptin have been disappointing. In this study we showed that human blood vessels express high levels of SSTR-1 with significantly lower levels of SSTR-2 and -4. Samples of normal veins and arteries, as well as atherosclerotic arteries, expressed predominantly SSTR-1. In addition, the levels of SSTR-1 varied between individuals, indicating that the vascular disease process may have affected SSTR gene expression. Immunocytochemical studies demonstrated that SSTR-1 was present in endothelial but not vascular smooth muscle cells. No evidence of SSTR-3 or -5 expression was detected in normal or diseased blood vessels. Two endothelial cell preparations, ECV304 and human umbilical vein endothelial cells, were investigated and shown to express only SSTR-1 and -4. Exposure of these cells to 10 nM somatostatin or 10 nM SSTR-1-specific agonist resulted in alterations to the actin cytoskeleton, as characterized by a loss of actin stress fibers coupled with an increase in lamellipodia formation at the plasma membrane. These results suggest that the lack of effectiveness of angiopeptin in humans may be due to the differential expression of SSTR-1 by human endothelial cells.

Mechanisms involved in the somatostatin-induced contraction of vascular smooth muscle cells

In experimental models and in humans, somatostatin (SRIF) is able to contract certain vascular structures. The present experiments were designed to assess the capacity of SRIF to contract cultured rat aortic vascular smooth muscle cells (VSMC), and to analyze the possible mechanisms involved. Cells incubated with SRIF showed a significant reduction in planar cell surface area, in a time- and dose-dependent manner. This effect was partially blocked by preincubating the cells with a combination of calcium antagonists (10 microM verapamil, plus 10 microM 3,4,5-Trimethoxybenzoic acid 3-(diethylanino) octyl ester TMB)-8). SRIF was also able to stimulate myosin light-chain phosphorylation in VSMC. A small but significant increase of intracellular calcium concentration, and decreased levels of cAMP, without changes in cGMP, were detected in VSMC incubated with SRIF. A search for the known SRIF receptors present in these cells, by reverse transcription-polymerase chain reaction, only SRIF receptor-4 was found to be present. These results demonstrate the ability of SRIF to contract cultured rat VSMC. The contraction observed in these cells appears to be due to a mixed mechanism, that involves [Ca2+]i and cAMP as second messengers, and is likely mediated via SRIF receptor-4.

Defective endothelially mediated pulmonary vasodilation in systemic sclerosis

STUDY OBJECTIVES

Obliterative pulmonary vascular disease manifested clinically as pulmonary hypertension (PHT) may complicate systemic sclerosis (SSc). The aim of this study was to investigate possible endothelial dysfunction in patients with SSC complicated by PHT.

DESIGN

Prospective, randomized trial.

SETTING

Postgraduate teaching hospital.

PATIENTS

Patients having SSc with PHT (SSc-PHT) and SSc without PHT (SSc), confirmed using Doppler echocardiography, and normal individuals (control subjects).

INTERVENTIONS

I.v. infusion of the endothelially dependent vasodilator, substance P (maximum dose, 100 pmol/min), and the nonendothelially dependent vasodilator, adenosine (maximum dose, 0.05 mg/kg/min).

MEASUREMENTS AND RESULTS

Effective pulmonary capillary blood flow (cardiac output minus right-to-left shunt) was measured in inert gas rebreathing, and calculated stroke index (SI) was used to reflect changes in pulmonary vascular resistance. During adenosine infusion, patients with SSc-PHT (n=5; mean age, 53+/-18 years) displayed a 25+/-16% increase in SI (p<0.05 compared with baseline), but no significant changes in SI were detected in the SSc (n=7; 54+/-6 years) or control (n=5; 35+/-5 years) groups. During infusion of substance P, SI rose by 32+/-18% in the control group at the maximum dose (p<0.05), but no change was observed in the SSc group. However, a fall in SI of -6+/-7% was detected in patients with SSc-PHT (p<0.05).

CONCLUSIONS

Substance P-mediated pulmonary vasodilation is absent in patients with systemic sclerosis, suggesting that endothelial dysfunction occurs early in the course of the illness, but some responsiveness to adenosine remains.

Neuropeptide Y-induced potentiation of noradrenergic vasoconstriction in the human saphenous vein: involvement of endothelium generated thromboxane

1. We investigated the potentiating effect of low concentrations of neuropeptide Y (NPY) on the vasoconstriction induced by transmural nerve stimulation (TNS) and noradrenaline (NA) in human saphenous veins. The effects of (i) endothelium removal; (ii) the addition of the NO pathway precursor L-arginine; (iii) the ET(A)/ET(B) endothelin receptor antagonist Ro 47-0203; (iv) the cyclo-oxygenase inhibitor, indomethacin; (v) the selective thromboxane A2 (TxA2) receptor antagonists Bay u3405 and ifetroban, and (vi) the TxA2 synthase inhibitor, UK 38485, were studied in order to gain information about the mechanisms of NPY-induced potentiation. 2. Contractile response curves for TNS (0.5-8 Hz) and for exogenously administered NA (0.1-3 microM) were obtained in superfused saphenous vein rings. The contractions induced by both TNS and NA at all tested frequencies and concentrations, respectively, were significantly potentiated by 50 nM NPY in endothelium intact veins. Conversely, in endothelium-denuded vessel rings the contractile-response curves to TNS and NA overlapped both in the absence and presence of NPY, thus suggesting that a release of vasoactive substances from endothelial cells could account for the noradrenergic NPY-induced potentiation. 3. In vessels with intact endothelium, the potentiating action of NPY on TNS and NA was unaffected by the presence of high concentrations of the NO precursor L-arginine (3-10 mM) or the non-selective ET(A)/ET(B) endothelin receptor antagonist, Ro 47-0203 (10 microM). These data indicate that the NPY-induced effect does not involve either the endothelium-derived vasodilator nitric oxide or the vasoconstrictor endothelin. Conversely, in the presence of the cyclo-oxygenase inhibitor, indomethacin (30 microM), NPY failed to potentiate the vasoconstrictions produced by either nerve stimulation or by exogenous NA, thus providing evidence that arachidonic acid metabolites through the cyclo-oxygenase pathway are mainly responsible for the potentiation evoked by NPY. 4. When the TxA2 receptor antagonists, Bay u 3405 (1 microM) and ifetroban (1 microM) were added to the superfusing medium, NPY did not alter either the frequency- or the concentration-response curves for either TNS or NA. Accordingly, both TNS- and NA-induced contractions were not potentiated by NPY in the presence of the TxA2 synthase inhibitor, UK 38485 (10 microM). This clearly demonstrates the pivotal role of TxA2 in NPY-induced potentiation. 5. In superfused vein rings with endothelium, a subthreshold concentration (0.2 nM) of the TxA2 mimetic U 46619 potentiated both TNS- and NA-induced vasoconstrictions. This potentiation was higher at low stimulation frequencies and low NA concentrations, and resembled that produced by NPY. 6. Our results indicate that in the human saphenous vein NPY potentiates the contractions produced by sympathetic nerve stimulation acting at the postjunctional level, primarily on endothelial cells. In particular, the NPY-induced release of a cyclo-oxygenase metabolite, namely TxA2, may have a synergistic effect on the vasoconstriction induced by the noradrenergic mediator. Thus, such a mechanism may play a key role in the maintenance of the sympathetic tone of large human capacitance vessels.

Inhibitory effect of somatostatin on the mechanosensitivity of articular afferents in normal and inflamed knee joints of the rat

The effect of somatostatin on the sensory activity of primary afferents was studied in normal and acutely inflamed rat knee joints. Fine afferent nerve fibers with conduction velocities of 0.9-18.0 m/s were recorded as single units. All nerve fibers tested responded to local mechanical stimulation, movements of the joint and i.a. injections of KCl (10(-4) mol, 0.1 ml) close to the joint. Somatostatin (10(-4) mol, 0.2 ml) caused no direct response of the units. In normal joints, somatostatin did not change the discharges evoked by non-noxious movements but decreased the responses to noxious movements significantly to about 63% of the responses before the application. In acutely inflamed joints, somatostatin reduced the discharges of non-noxious and of noxious movements to about 55% and 52%, respectively. Injections of somatostatin with lower concentrations (10(-6) mol, 10(-8) mol) i.a. close to inflamed joints revealed shorter and less pronounced reductions of the responses to noxious movements. In a proportion of afferents, substance P (10(-4) mol) and bradykinin (10(-4) mol) were able to increase these responses again. These data indicate that the mechanosensitivity of articular afferents in normal joints may also be regulated by several neuropeptides based on a balance of pro-inflammatory peptides such as substance P, and anti-inflammatory peptides such as somatostatin. In an inflamed joint, pro-inflammatory peptides seem to predominate resulting in a sensitization of the peripheral nerve fibers. In this case, an application of somatostatin or its analogues could be used clinically to compensate this effect.

Prejunctional neuropeptide Y receptors in human kidney and atrium

The aim of our study was to characterize functionally prejunctional neuropeptide Y (NPY) receptors in human and rabbit renal cortex, as well as in human right atrium. Segments of human atrial appendages and of human and rabbit renal cortex were preincubated with [3H]noradrenaline, superfused with Krebs-Henseleit solution and stimulated electrically in superfusion chambers. The stimulation-induced outflow of radioactivity was taken as an index of endogenous noradrenaline release. The effects of subtype-selective NPY analogs on the stimulation-induced noradrenaline release were studied. NPY, its endogenous analog, peptide YY, and its C-terminal fragment, NPY13-36, but not its analog, [Leu31,Pro34]NPY, concentration dependently (1-100 nM) inhibited [3H]noradrenaline release in all tissues studied. NPY-induced inhibition of [3H]noradrenaline release in human and rabbit kidney was abolished by pretreatment with pertussis toxin. We conclude that prejunctional inhibition of noradrenaline release in human heart and human and rabbit kidney occurs through NPY receptors of the Y2 subtype, which appear to couple to a pertussis toxin-sensitive G protein.

Direct renovascular effect of somatostatin in the dog

Recently, effects of somatostatin on the renal function have been described and the vasoactive properties of the peptide were proposed to contribute to this action. However, the available data on its effect in the renal vascular bed are very controversial. Therefore, we investigated the effect of local intaarterial somatostatin boluses in a wide range of doses (5 x 10(-11) - 5 x 10(-5) g) on the renal blood flow (RBF) in anesthetized dogs. RBF was measured by an electromagnetic flow probe. Somatostatin did not influence blood pressure or heart rate. RBF exhibited a significant, dose-dependent fall (ranging from 11.6 +/- 11.9% to 31.9 +/- 17.3%), with a threshold at a dose of 5 x 10(-10) g. These results offer conclusive evidence for the contribution of somatostatin-induced direct renal vasoconstriction to its renal effects, in addition to the demonstrated modulation of other vasoactive systems and tubular functions.

alpha-Thrombin upregulates G alpha i3 in human vascular endothelial cells

BACKGROUND AND PURPOSE

During thrombosis, alpha-thrombin becomes sequestered by fibrin and the subendothelial basement membrane, and it is available to interact with the vasculature over prolonged periods. In this study, we investigated the long-term effect of alpha-thrombin on G alpha i3 and G alpha s levels in human vascular endothelial cells (EC). Because obesity is associated with changes in receptor signaling in many animal models, we also explored the influence of this clinical risk factor.

METHODS

Primary cultures of human EC were exposed to alpha-thrombin for 16 hours, and immunologically detectable G alpha i3 and G alpha s levels were measured.

RESULTS

alpha-Thrombin (100 nmol/L) increased G alpha i3 levels in EC derived from the cerebral microvasculature and superficial temporal artery (4.2 +/- 1.2-fold and 2.8 +/- 0.32-fold, respectively) but had no significant effect on EC derived from omental artery (P > .6) or from the superficial temporal artery of obese (body mass index > or = 28 kg/m2) patients (P > .4). The expression of G alpha s was unchanged in all cell types (P > or = .1). Two other circulating peptides, vasoactive intestinal peptide and endothelin-1, failed to alter the expression of either G protein in EC from the cerebral microvasculature, further demonstrating the specificity of the alpha-thrombin effect. However, thrombin receptor activating protein-14 mimicked the alpha-thrombin response and increased G alpha i3 in EC derived from the cerebral microvasculature and superficial temporal artery.

CONCLUSIONS

We conclude that alpha-thrombin increases G alpha i3 expression in some EC through activation of its tethered liganded receptor. Obesity appears to suppress this action of alpha-thrombin.

Substance P in human hand veins in vivo: tolerance, efficacy, potency, and mechanism of venodilator action

OBJECTIVES

To study potency, efficacy, development of tolerance, and mechanism of action of substance P, an endothelium-dependent vasodilator neurokinin, in human hand veins in vivo.

METHODS

Thirty-three healthy subjects were studied with use of the hand vein compliance technique. In hand veins preconstricted with the alpha 1-agonist phenylephrine, substance P and antagonists of nitric oxide formation (L-NG-mono-methyl-arginine, L-NMMA), adenosine triphosphate (ATP)-dependent potassium channels (glyburide), angiotensin converting enzyme (enalaprilat), and cyclooxygenase (acetylsalicylic acid) were infused and the venodilator effect was measured.

RESULTS

Substance P proved to be the most potent venodilator known thus far (the dose-rate exerting 50% of mean maximum dilation [ED50], geometric mean: 0.105 pmol/min). Rapid development of tolerance occurred in seven of eight volunteers studied. Glyburide decreased the venodilator action of a single dose of substance P (1.5 pmol/min) from 81% to 28% of baseline venodilation (p < 0.05), suggesting that substance P acts through release of endothelium-derived hyperpolarizing factor. The cyclooxygenase-inhibitor acetylsalicylic acid reduced substance P-induced venodilation from 53% +/- 7% to 34% +/- 8% (p < 0.05), whereas L-NMMA had no effect.

CONCLUSIONS

Unlike in other vessels, substance P-induced venodilation in hand veins is not mediated through nitric oxide but to a significant extent through a glyburide-sensitive pathway. Therefore it appears likely that substance P activates ATP-dependent potassium channels on vascular smooth muscle cells through the release of endothelium-derived hyperpolarizing factor.

Tachykinin NK1 receptors mediate both vasoconstrictor and vasodilator responses in the rabbit isolated jugular vein

We have characterized the receptor(s) mediating contraction and relaxation produced by tachykinins in the rabbit isolated jugular vein. The tachykinin NK1 receptor-selective agonists septide and [Pro9]substance P produced concentration-dependent contractions which were potentiated by either the removal of the vascular endothelium (Emax = +106% and +72%, respectively) or by pretreatment with L-nitroarginine (100 microM; 60 min before) (Emax = +123% and +71%, respectively). The tachykinin NK1 receptor-selective antagonist, (+/-)-CP-96,345 ([2-(diphenylmethyl)-N-[(2-methoxyphenyl)-methyl]-1- azabicyclo[2,2,2]octan-3-amine]) (10-300 nM) competitively antagonized septide (pKB = 9.0) with 10-fold greater potency than [Pro9]substance P (pKB = 8.0). In preparations with intact endothelium both septide and [Pro9]substance P (from 0.1 to 100 nM) relaxed the noradrenaline-(10 microM) induced tone, and their effects were markedly reduced by (+/-)-CP-96,345 (100 nM). In noradrenaline-precontracted veins L-nitroarginine (100 microM) reversed the tachykinin-induced vasodilation into a contraction, providing evidence for the involvement of nitric oxide in this response. The tachykinin NK3 and NK2 receptor-selective agonists senktide and [beta Ala8]neurokinin A-(4-10) were either ineffective, or produced small effects antagonized by (+/-)-CP-96,345 (100 nM), respectively. In conclusion, tachykinin NK1 receptors mediate both tachykinin-induced contraction and relaxation in the rabbit jugular vein. This preparation, deprived of the endothelium or pretreated with L-nitroarginine, is suitable for evaluating tachykinin agonists or antagonists.

Vasoconstrictive action of neuropeptide Y in bone. The porcine tibia perfused in vivo

The hemodynamic effects of neuropeptide Y (NPY) and norepinephrine (NE) in bone were studied by infusion into the nutrient artery of an in vivo and in situ perfused tibia in 19 pigs. NPY and NE caused elevation of the perfusion pressure and decline in intraosseous pressure, which was evidence of intraosseous vasoconstriction. The study suggests that NPY, along with NE, acts as a sympathetic neurotransmitter in the control of vascular tone in bone.

The rabbit saphenous vein: a tissue preparation specifically enriched in NPY-Y1 receptor subtype

Neuropeptide Y (NPY), a co-transmitter in noradrenergic sympathetic nerves of the cardiovascular system, was tested on isolated segments of rabbit saphenous vein. NPY caused strong, long lasting and concentration dependent contraction resistant to adrenergic blockade. PYY, a NPY related peptide, shared this property. As pressor agents, both peptides were about 100-fold more potent than norepinephrine and at their highest concentrations caused a contraction of a similar magnitude as NE. Gradual shortening of N-terminal end of the NPY molecule caused major loss of potency and reduction of intrinsic activity; which suggests that the entire molecule is required to produce full biological activity in this vascular preparation. Addition of [Leu31,Pro34]pNPY, a NPY analog with specific agonist properties at Y1 receptors, mimicked the effect of NPY whereas NPY (13-36), a selective agonist at Y2 receptors, caused a 2 log unit shift to the right of the concentration response curve. These results suggest that the vasoconstrictor effect of NPY in rabbit saphenous vein results from a direct effect on smooth muscle cells and that the receptors involved are of the Y1 subtype.