Cutaneous vasomotor effects of neuropeptide Y

Elevated levels of neuropeptide Y in preeclampsia: A pilot study implicating a role for stress in pathogenesis of the disease

OBJECTIVE

To determine if preeclampsia (PE) is associated with dysregulation of the neuropeptide Y (NPY) system.

METHODS

The study enrolled 114 subjects either with normal pregnancy (NP) or with PE. Systolic blood pressure (SBP) was collected from patients using a standard sphygmomanometer. The PE patients were divided into two groups based on the gestational age (GA) at delivery - placental PE (PLPE, GA <34 weeks) or maternal PE (MTPE, GA ≥34 weeks). NPY was measured in platelet rich plasma (PRP), platelet poor plasma (PPP) and in the serum of NP and PE patients utilizing radioimmunoassay. Serum levels of soluble fms-like tyrosine kinase-1 (sFlt-1) and placental growth factor (PlGF) were measured in NP and PE subjects by ELISA.

RESULTS

SBP was higher in PE compared to NP. Circulating NPY in serum and PRP, as well as NPY content per 100,000 platelets, but not its concentrations in PPP, were elevated in PE, as compared to NP. The highest NPY concentrations were observed in sera and PRP of patients with MTPE. PE patients had also elevated levels of sFlt-1, as compared to NP, although no difference between PLPE and MTPL groups were observed. There was no increase in P1GF in PE patients.

CONCLUSION

Systemic NPY is elevated in PE patients, as compared to NP. This increase is observed in blood fractions containing platelets, suggesting accumulation of the peptide in these cells. NPY concentrations are particularly high in patients with MTPE, underlying differences in etiology between PLPE and MTPE. Our study implicates NPY as a potential target in antihypertensive therapies for PE patients.

Cutaneous vasodilator and vasoconstrictor mechanisms in temperature regulation

In this review, we focus on significant developments in our understanding of the mechanisms that control the cutaneous vasculature in humans, with emphasis on the literature of the last half-century. To provide a background for subsequent sections, we review methods of measurement and techniques of importance in elucidating control mechanisms for studying skin blood flow. In addition, the anatomy of the skin relevant to its thermoregulatory function is outlined. The mechanisms by which sympathetic nerves mediate cutaneous active vasodilation during whole body heating and cutaneous vasoconstriction during whole body cooling are reviewed, including discussions of mechanisms involving cotransmission, NO, and other effectors. Current concepts for the mechanisms that effect local cutaneous vascular responses to local skin warming and cooling are examined, including the roles of temperature sensitive afferent neurons as well as NO and other mediators. Factors that can modulate control mechanisms of the cutaneous vasculature, such as gender, aging, and clinical conditions, are discussed, as are nonthermoregulatory reflex modifiers of thermoregulatory cutaneous vascular responses.

Role of neuropeptides, neurotrophins, and neurohormones in skin wound healing

Due to the close interactions between the skin and peripheral nervous system, there is increasing evidence that the cutaneous innervation is an important modulator of the normal wound healing process. The communication between sensory neurons and skin cells involves a variety of molecules (neuropeptides, neurohormones, and neurotrophins) and their specific receptors expressed by both neuronal and nonneuronal skin cells. It is well established that neurotransmitters and nerve growth factors released in skin have immunoregulatory roles and can exert mitogenic actions; they could also influence the functions of the different skin cell types during the wound healing process.

In vivo mechanisms of cutaneous vasodilation and vasoconstriction in humans during thermoregulatory challenges

This review focuses on the neural and local mechanisms that have been demonstrated to effect cutaneous vasodilation and vasoconstriction in response to heat and cold stress in vivo in humans. First, our present understanding of the mechanisms by which sympathetic cholinergic nerves mediate cutaneous active vasodilation during reflex responses to whole body heating is discussed. These mechanisms include roles for cotransmission as well as nitric oxide (NO). Next, the mechanisms by which sympathetic noradrenergic nerves mediate cutaneous active vasoconstriction during whole body cooling are reviewed, including cotransmission by neuropeptide Y (NPY) acting through NPY Y1 receptors. Subsequently, current concepts for the mechanisms that effect local cutaneous vascular responses to direct skin warming are examined. These mechanisms include the roles of temperature-sensitive afferent neurons as well as NO in causing vasodilation during local heating of skin. This section is followed by a review of the mechanisms that cause local cutaneous vasoconstriction in response to direct cooling of the skin, including the dependence of these responses on intact sensory and sympathetic, noradrenergic innervation as well as roles for nonneural mechanisms. Finally, unresolved issues that warrant further research on mechanisms that control cutaneous vascular responses to heating and cooling are discussed.

Neuropeptide Y antagonism reduces reflex cutaneous vasoconstriction in humans

Previous studies have provided evidence of a non-noradrenergic contributor to reflex cutaneous vasoconstriction in humans but did not identify the transmitter responsible. To test whether neuropeptide Y (NPY) has a role, in two series of experiments we slowly reduced whole body skin temperature (TSK) from 34.5 to 31.7 degrees C. In protocol 1, Ringer solution and the NPY receptor antagonist BIBP-3226 alone were delivered intradermally via microdialysis. In protocol 2, yohimbine plus propranolol (Yoh + Pro), Yoh + Pro in combination with BIBP-3226, and Ringer solution were delivered to antagonize locally the vasomotor effects of NPY and norepinephrine. Blood flow was measured by laser Doppler flowmetry (LDF). Mean arterial blood pressure (MAP) was monitored at the finger (Finapres). In protocol 1, cutaneous vascular conductance (CVC) fell by 45%, to 55.1 +/- 5.6% of baseline at control sites (P < 0.05). At BIBP-3226-treated sites, CVC fell by 34.1% to 65.9 +/- 5.0% (P < 0.05; P < 0.05 between sites). In protocol 2, during body cooling, CVC at control sites fell by 32.6%, to 67.4 +/- 4.3% of baseline; at sites treated with Yoh + Pro, CVC fell by 18.7%, to 81.3 +/- 4.4% of baseline (P < 0.05 vs. baseline; P < 0.05 vs. control) and did not fall significantly at sites treated with BIBP-3226 + Yoh + Pro (P > 0.05; P < 0.05 vs. other sites). After cooling, exogenous norepinephrine induced vasoconstriction at control sites (P < 0.05) but not at sites treated with Yoh + Pro + BIBP-3226 (P > 0.05). These results indicate that NPY participates in sympathetically mediated cutaneous vasoconstriction in humans during whole body cooling.

Stimulation of NPY Y2 receptors by PYY3-36 reveals divergent cardiovascular effects of endogenous NPY in rats on different dietary regimens

In the present experiments the gut hormone peptide YY3-36 (PYY3-36), which inhibits neuropeptide Y (NPY) release, was used as a tool to study the cardiovascular effects of endogenous NPY under different dietary regimens in rats instrumented with a telemetry transmitter. In a first experiment, rats were placed on a standard chow diet ad libitum and in a second experiment on a high-fat diet ad libitum. After 6 wk, PYY3-36 (300 μg/kg) or vehicle was injected intraperitoneally. In a third experiment, PYY3-36 or vehicle was administered after 14 days of 50% restriction of a standard chow diet. In food-restricted rats, PYY3-36 increased mean arterial pressure (7 ± 1 mmHg, mean ± SE, P < 0.001 vs. saline, 1-way repeated-measures ANOVA with Bonferroni t-test) and heart rate (22 ± 4 beats/min, P < 0.001) during 3 h after administration. Conversely, PYY3-36 did not influence mean arterial pressure (0 ± 1 mmHg) and heart rate (-8 ± 5 beats/min) significantly in rats on a high-fat diet. Rats fed standard chow diet ad libitum showed an intermediate response (mean arterial pressure 4 ± 1 mmHg, P < 0.05, and heart rate 5 ± 2 beats/min, not significant). Thus, in our studies, divergent cardiovascular responses to PYY3-36 were observed in rats on different dietary regimens. These findings suggest that the cardiovascular effects of PYY3-36 depend on the hypothalamic NPY release, which is increased after chronic food restriction and decreased during a high-fat diet.

The ability of neuropeptide Y to mediate responses in the murine cutaneous microvasculature: an analysis of the contribution of Y1 and Y2 receptors

1. The ability of neuropeptide Y (NPY) to modulate skin blood flow, oedema formation and neutrophil accumulation was investigated. Experiments were designed to examine the possible contribution of the Y2 receptor, in addition to the Y1 receptor, through use of Y2 receptor knockout mice (Y2-/-) and selective receptor antagonists. 2. The development of a 99mTc clearance technique for the measurement of microvascular blood flow changes in mouse dorsal skin revealed a dose-dependent ability of picomole amounts of NPY, and also of the Y1-preferred agonist Pro34NPY and the Y2-preferred agonist PYY(3-36) to decrease blood flow. 3. The Y1 receptor antagonist BIBO3304 blocked responses to the Y1 agonist at the lower doses, but only partially inhibited at the higher doses tested in Y2+/+. In Y2-/- receptor mice, the responses to the Y2 agonist were abolished at the lower doses and partially reduced at the highest dose tested, while those to the Y1 agonist were similar in both Y2+/+ and Y2-/-receptor mice. 4. In Y2+/+ receptor mice, the simultaneous injection of the Y2 antagonist BIIE0246 with BIBO3304 abolished Y2 agonist-induced decreases in blood flow over the dose range used (10-100 pmol). When the Y2 receptor antagonist BIIE0246 was given alone, it was not able to significantly affect the PYY(3-36)-induced response, whereas the Y1 receptor antagonist BIBO3304 partially (P<0.001) inhibited the decrease in blood flow evoked by PYY(3-36) at the highest dose. 5. NPY did not mediate either oedema formation, even when investigated in the presence of the vasodilator calcitonin gene-related peptide (CGRP), or neutrophil accumulation in murine skin. 6. We conclude that the major vasoactive activity of NPY in the cutaneous microvasculature is to act in a potent manner to decrease blood flow via Y1 receptors, with evidence for the additional involvement of postjunctional Y2 receptors. Our results do not provide evidence for a potent proinflammatory activity of NPY in the cutaneous microvasculature.

Neuropeptídeos na pele

Há evidências crescentes de que a inervação cutânea é capaz de modular uma variedade de fenômenos cutâneos agudos e crônicos, interagindo com as células da pele e seus componentes imunes. Essa forma de sinalização local entre tecido nervoso e tecido cutâneo ocorre especialmente por meio dos neuropeptídeos, uma numerosa família de neurotransmissores de natureza química comum e nomenclatura heterogênea presentes em todo o sistema nervoso e secretados pelas fibras nervosas cutâneas. São alvo desta revisão os neuropeptídeos substância P (SP), o peptídeo relacionado ao gene da calcitonina (CGRP), o peptídeo vasoativo intestinal (VIP), o peptídeo ativador da adenilato-ciclase pituitária (PACAP), o neuropeptídeo Y (NPY) e a somatostatina (SOM). Serão discutidas suas ações sobre as células da pele e sistema imune, bem como estudos recentes que sugerem a participação dos neuropeptídeos nas respostas inflamatórias cutâneas, nas reações de hipersensibilidade e em dermatoses humanas, notadamente na psoríase, dermatite atópica, hanseníase e alopecia.

Skin blood flow in adult human thermoregulation: how it works, when it does not, and why

The thermoregulatory control of human skin blood flow is vital to the maintenance of normal body temperatures during challenges to thermal homeostasis. Sympathetic neural control of skin blood flow includes the noradrenergic vasoconstrictor system and a sympathetic active vasodilator system, the latter of which is responsible for 80% to 90% of the substantial cutaneous vasodilation that occurs with whole body heat stress. With body heating, the magnitude of skin vasodilation is striking: skin blood flow can reach 6 to 8 L/min during hyperthermia. Cutaneous sympathetic vasoconstrictor and vasodilator systems also participate in baroreflex control of blood pressure; this is particularly important during heat stress, when such a large percentage of cardiac output is directed to the skin. Local thermal control of cutaneous blood vessels also contributes importantly--local warming of the skin can cause maximal vasodilation in healthy humans and includes roles for both local sensory nerves and nitric oxide. Local cooling of the skin can decrease skin blood flow to minimal levels. During menopause, changes in reproductive hormone levels substantially alter thermoregulatory control of skin blood flow. This altered control might contribute to the occurrence of hot flashes. In type 2 diabetes mellitus, the ability of skin blood vessels to dilate is impaired. This impaired vasodilation likely contributes to the increased risk of heat illness in this patient population during exposure to elevated ambient temperatures. Raynaud phenomenon and erythromelalgia represent cutaneous microvascular disorders whose pathophysiology appears to relate to disorders of local and/or reflex thermoregulatory control of the skin circulation.

Distribution of neuropeptide Y Y1 receptors in rodent peripheral tissues

Using a sensitive immunohistochemical technique, the localization of neuropeptide Y (NPY) Y1-receptor (Y1R)-like immunoreactivity (LI) was studied in various peripheral tissues of rat. Wild-type (WT) and Y1R-knockout (KO) mice were also analyzed. Y1R-LI was found in small arteries and arterioles in many tissues, with particularly high levels in the thyroid and parathyroid glands. In the thyroid gland, Y1R-LI was seen in blood vessel walls lacking alpha-smooth muscle actin, i.e., perhaps in endothelial cells of capillaries. Larger arteries lacked detectable Y1R-LI. A distinct Y1R-immunoreactive (IR) reticulum was seen in the WT mouse spleen, but not in Y1R-KO mouse or rat. In the gastrointestinal tract, Y1R-positive neurons were observed in the myenteric plexus, and a few enteroendocrine cells were Y1R-IR. Some cells in islets of Langerhans in the pancreas were Y1R-positive, and double immunostaining showed coexistence with somatostatin in D-cells. In the urogenital tract, Y1R-LI was observed in the collecting tubule cells of the renal papillae and in some epithelial cells of the seminal vesicle. Some chromaffin cells of adrenal medulla were positive for Y1R. The problem of the specificity of the Y1R-LI is evaluated using adsorption tests as well as comparisons among rat, WT mouse, and mouse with deleted Y1R. Our findings support many earlier studies based on other methodologies, showing that Y1Rs on smooth muscle cells of blood vessels mediate NPY-induced vasoconstriction in various organs. In addition, Y1Rs in other cells in parenchymal tissues of several organs suggest nonvascular effects of NPY via the Y1R.

Langerhans cell expression of neuropeptide Y and peptide YY

Neuropeptide Y (NPY) and peptide YY (PYY) are structurally related peptides with a variety of known functions. The role of these peptides in the skin is largely unknown, although NPY-like immunoreactivity has been reported in the epidermis. The recent report that these peptides have antimicrobial properties suggests that NPY and PYY may contribute to the skin's defense mechanisms against invading microorganisms. We have demonstrated that Langerhans cells (LC) and a certain BALB/c epidermis-derived dendritic cell line contain mRNA for NPY and PYY using RT-PCR. Furthermore, this dendritic cell line as well as an epidermis-derived dendritic cell line from A/J mice were found to produce NPY and PYY and LC produced PYY, as assessed by radioimmunoassay. These data suggest that the protective function of LC include not only antigen presentation, but also production of antimicrobial peptides.

Sympathetic nonnoradrenergic cutaneous vasoconstriction in women is associated with reproductive hormone status

We tested whether a nonnoradrenergic component of reflex vasoconstriction of skin blood flow (SkBF) is sensitive to female reproductive hormones. Six women taking oral contraceptives underwent whole-body cooling during high-hormone (HH) and low-hormone (LH) phases of oral contraceptive use. SkBF was monitored by laser Doppler flowmetry (LDF) at sites treated by intradermal injection of yohimbine-propranolol (5 mM and 1 mM; YOPR) to block the effects of norepinephrine (NE) or at saline (Sal) control sites. Mean arterial pressure (MAP) was measured with the use of the Penaz method. Cutaneous vascular conductance (CVC = LDF/mean arterial pressure) was expressed as a percentage of baseline. Whole body skin temperature was decreased from 34 to 31 degrees C in HH and LH. In both HH and LH, CVC at Sal-treated sites was reduced during cooling (CVC = 53.1 +/- 8.6% and 54.4 +/- 4.2%, both P < 0.05). In HH, CVC at YOPR sites was reduced during cooling (78.8 +/- 3.6%, P < 0.05). In contrast, CVC at YOPR sites was not reduced significantly during cooling in LH (CVC = 95.9 +/- 2.8%, P > 0.05). Across phases, CVC at YOPR sites during cooling was significantly different (P < 0.05). After cooling, the effects of NE at YOPR sites were completely blocked. These data indicate that a nonnoradrenergic mechanism of reflex cutaneous vasoconstriction is present in women and is associated with reproductive hormone status.

Nonnoradrenergic mechanism of reflex cutaneous vasoconstriction in men

We tested for a nonnoradrenergic mechanism of reflex cutaneous vasoconstriction with whole body progressive cooling in seven men. Forearm sites (<1 cm(2)) were pretreated with: 1) yohimbine (Yoh; 5 mM id) to antagonize alpha-adrenergic receptors, 2) Yoh plus propranolol (5 mM Yoh-1 mM PR id) to block alpha- and beta-adrenergic receptors, 3) iontophoretic application of bretylium tosylate (BT) to block all sympathetic vasoconstrictor nerve effects, or 4) intradermal saline. Skin blood flow was measured by laser Doppler flowmetry and arterial pressure by finger photoplethysmography; cutaneous vascular conductance (CVC) was indexed as the ratio of the two. Whole body skin temperature (T(SK)) was controlled at 34 degrees C (water-perfused suit) for 10 min and then lowered to 31 degrees C over 15 min. During cooling, vasoconstriction was blocked at BT sites (P > 0.05). CVC at saline sites fell significantly beginning at T(SK) of 33.4 +/- 0.01 degrees C (P <0.05). CVC at Yoh-PR sites was significantly reduced beginning at TSK of 33.0 +/- 0.01 degrees C (P < 0.05). After cooling, iontophoretic application of norepinephrine (NE) confirmed blockade of adrenergic receptors by Yoh-PR. Because the effects of NE were blocked at sites showing significant reflex vasoconstriction, a nonnoradrenergic mechanism in human skin is indicated, probably via a sympathetic cotransmitter.

Expression of neuropeptide Y receptors mRNA and protein in human brain vessels and cerebromicrovascular cells in culture

Neuropeptide Y (NPY) has been suggested as an important regulator of CBF. However, except for the presence of Y1 receptors in large cerebral arteries, little is known about its possible sites of action on brain vessels. In this study, we sought to identify the NPY receptors present in the human cerebrovascular bed. Specific Y1 receptor binding sites, localized on the smooth muscle of human pial vessels and potently competed by NPY, polypeptide YY (PYY), and the selective Y1 receptor antagonist BIBP 3226, were identified by quantitative radioautography of the Y1 radioligand [125I]-[Leu31, Pro34]-PYY. In contrast, no specific binding of the Y2-([125I]-PYY3-36) and Y4/Y5-(125I-human pancreatic polypeptide [hPP]) radioligands could be detected. By in situ hybridization, expression of Y1 receptor mRNA was restricted to the smooth muscle layer of pial vessels, whereas no specific signals were detected for either Y2, Y4, or Y5 receptors. Similarly, using reverse transcriptase-polymerase chain reaction (RT-PCR), mRNA for Y1 but not Y2, Y4, or Y5 receptors was consistently detected in isolated human pial vessels, intracortical microvessels, and capillaries. In human brain microvascular cells in culture, PCR products for the Y1 receptors were exclusively found in the smooth muscle cells. In cultures of human brain astrocytes, a cell type that associates intimately with brain microvessels, PCR products for Y1, Y2, and Y4 but not Y5 receptors were identified. Finally, NPY significantly inhibited the forskolin-induced cAMP production in smooth muscle but not in endothelial cell cultures. We conclude that smooth muscle Y1 receptors are the primary if not exclusive NPY receptors associated with human brain extraparenchymal and intraparenchymal blood vessels, where they most likely mediate cerebral vasoconstriction.

Distribution and coexistence of neuropeptides in nerve fibres in the temporomandibular joint of late gestation fetal sheep

The density and distribution of nerve fibres immunoreactive to antisera for PGP 9.5 (general neuronal marker), calcitonin gene related peptide (CGRP) and substance P (SP) (markers for sensory neurons), as well as neuropeptide Y (NPY), vasoactive intestinal peptide (VIP) and tyrosine hydroxylase (TH) (markers for autonomic fibres), were examined in the temporomandibular joint (TMJ) of late gestation fetal sheep. This work formed part of a project investigating the influence of age and osteoarthritis on the innervation of the TMJ, and was undertaken to determine whether the innervation of the joint at 140 d gestation (17 d before birth) differed from that in the mature adult. Immunofluorescence microscopy was applied to serial sections of the capsule, disc and synovial membrane of 10 joints from 5 fetuses and image analysis was used for the quantitative assessment. The capsule, synovial membrane and the disc contained fibres immunoreactive (IR) to antisera for PGP 9.5, SP and CGRP. NPY-IR fibres were only visible in the loose connective tissue of the capsule. No VIP- or TH-IR nerve fibres were detected in the fetal TMJ. There was no statistically detectable difference between the density of nerve fibres immunoreactive to CGRP or PGP 9.5 antisera in the capsule or disc. Substance P-immunoreactivity (IR) was relatively weak in all samples examined. Scattered branches of CGRP-IR fibres were found deep in the disc proper. The lack of receptor endings, other than free nerve endings in the TMJ of the late fetal sheep, might be a reflection of the functional and anatomical immaturity of the TMJ, as reflected in the immature, gross and microscopic appearance of the disc, the inferior joint compartment and articular surface of the condyle at this stage. These results demonstrate that the capsule, synovial membrane and disc in the TMJ of fetal sheep at 140 d gestation age are innervated with sensory fibres, while autonomic fibres are located in the capsule only. The findings also support the view that the disc is innervated at an early stage of life but at a later stage the density of innervation in the central part of the disc regresses and the innervation remains only peripherally in the adult TMJ disc. Further work is required to determine (1) at what stage sympathetic fibres innervate the disc and the synovium, and (2) when the mechanoreceptive nerve endings develop.

Hemodynamic profile of neuropeptide Y in dogs: effect of ganglionic blockade

The hemodynamic effects of neuropeptide Y (NPY) were examined over a dose range of 0.03-30 nmol/kg, i.v., in anesthetized open-chest, ventilated dogs with and without ganglionic blockade. In normal (non-ganglion-blocked) animals, NPY produced significant, dose-dependent, and sustained (lasting 15-45 min) increases in mean arterial blood pressure and systemic vascular resistance (SVR) with a threshold dose of 0.3 nmol/kg and a maximum effective dose of 10 nmol/kg. Cardiac index (CI) decreased at doses > 1 nmol/kg, but stroke volume was not altered; heart rate (HR) decreased significantly at and above the 3 nmol/kg dose. No significant changes were observed in the left ventricular dP/dt (LVdP/dt) or the contractility index (LVdP/dt divided by systolic pressure). In ganglion-blocked animals, pressor and SVR responses to NPY were similar to those seen in normal animals but HR was not affected and a small but significant decrease in CI was seen only at the 30 nmol/kg. Furthermore, whereas LVdP/dt of ganglion-blocked dogs increased significantly at and above the 1 nmol/kg dose, the contractility index increased slightly only with the 10 and 30 nmol/kg doses. These data indicate that NPY produces sustained hypertension in dogs secondary to peripheral vasoconstriction, has a weak, direct positive inotropic action on the heart, and lacks chronotropic effects.