A study of nerves containing peptides in the pulmonary vasculature of healthy infants and children and of those with pulmonary hypertension

Device-based neuromodulation for cardiovascular diseases and patient' s age

The autonomic nervous system plays an important role in the pathogenesis of cardiovascular diseases. With aging, autonomic activity changes, and this impacts the physiological reactions to internal and external signals. Both sympathetic and parasympathetic responses seem to decline, reflecting functional and structural changes in nervous regulation. Although some investigators suggested that both the sympathetic and parasympathetic activities were suppressed, others found that only the parasympathetic activity was suppressed while the sympathetic activity increased. In addition, cardiac innervation progressively diminishes with aging. Therefore, one may suggest that neuromodulation interventions may have different effects, and older age groups can express an attenuated response. This article aims to discuss the effect of device-based neuromodulation in different cardiovascular diseases, depending on the patient's age. Thus, we cover renal denervation, pulmonary artery denervation, baroreceptor activation therapy, vagus nerve stimulation, spinal cord stimulation, ganglionated plexi ablation for the management of arterial and pulmonary hypertension, heart failure, angina and arrhythmias. The results of many clinical studies appeared to be unconvincing. In view of the low rate of positive findings in clinical studies incorporating neuromodulation approaches, we suggest the underestimation of advanced age as a potential contributing factor to poorer response. Analysis of outcomes between different age groups in clinical trials may shed more light on the true effects of neuromodulation when neutral/ambiguous results are obtained.

Innervation in organogenesis

Proper innervation of peripheral organs helps to maintain physiological homeostasis and elicit responses to external stimuli. Disruptions to normal function can result in pathophysiological consequences. The establishment of connections and communication between the central nervous system and the peripheral organs is accomplished through the peripheral nervous system. Neuronal connections with target tissues arise from ganglia partitioned throughout the body. Organ innervation is initiated during development with stimuli being conducted through several types of neurons including sympathetic, parasympathetic, and sensory. While the physiological modulation of mature organs by these nerves is largely understood, their role in mammalian development is only beginning to be uncovered. Interactions with cells in target tissues can affect the development and eventual function of several organs, highlighting their significance. This chapter will cover the origin of peripheral neurons, factors mediating organ innervation, and the composition and function of organ-specific nerves during development. This emerging field aims to identify the functional contribution of innervation to development which will inform future investigations of normal and abnormal mammalian organogenesis, as well as contribute to regenerative and organ replacement efforts where nerve-derived signals may have significant implications for the advancement of such studies.

An Ovine Model for Percutaneous Pulmonary Artery Laser Denervation: Perivascular Innervation and Ablation Lesion Characteristics

Background: Pulmonary artery denervation (PADN) is an evolving interventional procedure capable to reduce pulmonary artery (PA) pressure. We aimed to compare PA nerve distribution in different specimens and assess the feasibility of an ovine model for a denervation procedure and evaluate the acute changes induced by laser energy. Methods: The experiment was divided into two phases: (1) the analysis of PA nerve distribution in sheep, pigs, and humans using histological and immunochemical methods; (2) fiberoptic PADN in sheep and postmortem laser lesion characteristics. Results: PA nerve density and distribution in sheep differ from humans, although pigs and sheep share similar characteristics, nerve fibers are observed in the media layer, adventitia, and perivascular tissue in sheep. Necrosis of the intima and focal hemorrhages within the media, adventitia, and perivascular adipose tissue were evidenced post laser PADN. Among the identified lesions, 40% reached adventitia and could be classified as effective for PADN. The use of 20 W ablation energy was safer and 30 W-ablation led to collateral organ damage. Conclusions: An ovine model is suitable for PADN procedures; however, nerve distribution in the PA bifurcation and main branches differ from human PA innervation. Laser ablation can be safely used for PADN procedures.

Upregulation of neuropeptides and obstructive airway disorder in infancy: A review with focus on post-RSV wheezing and NEHI

Obstructive airway disorders, common in infancy and early childhood, include some entities that are recognized to have neuro immune mediators as their underlying pathogenetic mechanisms. The best characterized example amongst post-viral wheezing phenotypes is the disorder that follows respiratory syncytial virus (RSV) infection and leads to intermittent, long-term wheezing. The underlying mechanisms of the airway reactivity related to RSV infection have been extensively studies and are associated with dysregulation of the nonadrenergic-noncholinergic (NANC) system, via upregulation of neurotransmitters, typically Substance P. Neuroendocrine hyperplasia of infancy (NEHI), while a less common entity, is a disorder characterized by more severe and long-term obstructive airway disease. NEHI is pathophysiologically characterized by abundance of neuroendocrine cells in the airways containing the neuroimmune mediator bombesin, the release of which is presumed to be the driver of the persistent small airway obstruction and functional air-trapping. Here we review the NANC and neuroendocrine cells, the neurotransmitter systems and their studied roles in pulmonary diseases with a focus on their role in lung development, and subsequent various pediatric lung diseases. We focus on the juxtaposition of the separate neuroimmune mechanisms underlying the pathogenesis of post-RSV recurrent wheezing and NEHI's persistent small airway obstruction. We finally propose a unifying concept of neuropeptides in obstructive disorders that may encompass these two entities and possibly others.

Lung Circulation

The circulation of the lung is unique both in volume and function. For example, it is the only organ with two circulations: the pulmonary circulation, the main function of which is gas exchange, and the bronchial circulation, a systemic vascular supply that provides oxygenated blood to the walls of the conducting airways, pulmonary arteries and veins. The pulmonary circulation accommodates the entire cardiac output, maintaining high blood flow at low intravascular arterial pressure. As compared with the systemic circulation, pulmonary arteries have thinner walls with much less vascular smooth muscle and a relative lack of basal tone. Factors controlling pulmonary blood flow include vascular structure, gravity, mechanical effects of breathing, and the influence of neural and humoral factors. Pulmonary vascular tone is also altered by hypoxia, which causes pulmonary vasoconstriction. If the hypoxic stimulus persists for a prolonged period, contraction is accompanied by remodeling of the vasculature, resulting in pulmonary hypertension. In addition, genetic and environmental factors can also confer susceptibility to development of pulmonary hypertension. Under normal conditions, the endothelium forms a tight barrier, actively regulating interstitial fluid homeostasis. Infection and inflammation compromise normal barrier homeostasis, resulting in increased permeability and edema formation. This article focuses on reviewing the basics of the lung circulation (pulmonary and bronchial), normal development and transition at birth and vasoregulation. Mechanisms contributing to pathological conditions in the pulmonary circulation, in particular when barrier function is disrupted and during development of pulmonary hypertension, will also be discussed.

NPY/Y₁ receptor-mediated vasoconstrictory and proliferative effects in pulmonary hypertension

BACKGROUND AND PURPOSE

Pulmonary arteries (PAs) are innervated, but little is known about the role of neuronal axis in pulmonary hypertension (PH). Here, we have examined the role of the neuropeptide Y (NPY) and its Y₁ receptor in PH pathogenesis.

EXPERIMENTAL APPROACH

NPY was localized by immunofluorescence. Expression of NPY and Y₁ receptor were determined by quantitative PCR. Cellular response to NPY stimulation was assessed by Western blotting, thymidine incorporation and calcium imaging. Wire myography and isolated perfused mouse lung were applied to study pulmonary vasoactive effects of NPY. Selective receptor antagonists were used to assess the contribution of receptor subtypes in mediating NPY effects.

KEY RESULTS

Samples from PH patients showed increased NPYergic innervation within the PA wall and higher Y₁ receptor expression, compared with donors. However, NPY levels were unchanged in both PA and serum. In the chronic hypoxic mouse model, Y₁ receptor were up-regulated, while expression of both NPY and Y₁ receptor was increased in the lungs of monocrotaline and SU5416-hypoxia rats. On a functional level, NPY acutely increased intracellular calcium levels and enhanced vasoconstriction of lung vessels preconstricted with adrenaline. Furthermore, NPY stimulated proliferation of human pulmonary arterial smooth muscle cells and activated p38 and PKD pathways. Correspondingly, higher phosphorylation of PKD was observed in remodelled vessels from PH patients. The selective Y₁ receptor antagonist, BIBO 3304, concentration-dependently inhibited vasoconstrictive and proliferative effects of NPY.

CONCLUSIONS AND IMPLICATIONS

NPY and Y₁ receptor are possible mediators of both vasoconstriction and pulmonary vascular remodelling in PH.

Structure and composition of pulmonary arteries, capillaries, and veins

The pulmonary vasculature comprises three anatomic compartments connected in series: the arterial tree, an extensive capillary bed, and the venular tree. Although, in general, this vasculature is thin-walled, structure is nonetheless complex. Contributions to structure (and thus potentially to function) from cells other than endothelial and smooth muscle cells as well as those from the extracellular matrix should be considered. This review is multifaceted, bringing together information regarding (i) classification of pulmonary vessels, (ii) branching geometry in the pulmonary vascular tree, (iii) a quantitative view of structure based on morphometry of the vascular wall, (iv) the relationship of nerves, a variety of interstitial cells, matrix proteins, and striated myocytes to smooth muscle and endothelium in the vascular wall, (v) heterogeneity within cell populations and between vascular compartments, (vi) homo- and heterotypic cell-cell junctional complexes, and (vii) the relation of the pulmonary vasculature to that of airways. These issues for pulmonary vascular structure are compared, when data is available, across species from human to mouse and shrew. Data from studies utilizing vascular casting, light and electron microscopy, as well as models developed from those data, are discussed. Finally, the need for rigorous quantitative approaches to study of vascular structure in lung is highlighted.

Hypoxic pulmonary vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Autonomic denervation and the origins of chronic Western diseases

Many chronic Western diseases result from lifestyles that include refined diets, poor bowel habits, limited physical exercise and suboptimal patterns of childbirth. Western diets result in reduced stool weights, increased bowel transit times and persistent physical efforts during defaecation. Prolonged physical efforts during defaecation and childbirth cause latent, or direct, injuries to branches of the cardiac (thorax), coeliac (abdomen) and hypogastric (pelvis) plexi. Injuries to autonomic nerves result in impaired visceral function including visceral dysmotility, tissue hypoplasia and hyperplasia, increased susceptibility to infection, and, aberrant reinnervation with sensitisation of the central nervous system (CNS). These unrecognised injuries are vulnerable to the long list of causes of autonomic Dysfunction, e.g. stress, alcohol, drugs, infection, trauma, cancer, etc. Specific injuries at different anatomical locations in midline autonomic pathways give rise to a wide range of Western diseases from infancy to old age, through diverse and cumulative mechanisms.

Regional heterogeneity of substance P-induced endothelium-dependent contraction, relaxation, and -independent contraction in rabbit pulmonary arteries

AIMS

The present study examined whether substance P (SP)-induced endothelium-dependent TXA(2)-mediated contraction (EDC), nitric oxide (NO)-mediated relaxation (EDR), and endothelium-independent contraction (EIC) are different between the rabbit proximal and distal intrapulmonary arteries.

MAIN METHODS

The helically cut strips of isolated proximal and distal arteries were fixed vertically between hooks in organ bath, and changes in isometric tension were measured.

KEY FINDINGS

SP-induced EDC was greater in the distal than proximal arteries, and EDR was greater in the proximal than distal arteries. However, under the complete blockade of NK(2) receptors and NO production, SP (10(-9)-3x10(-7) M)-induced EDC did not differ between proximal and distal arteries. Under the complete blockade of NK(2) receptors and TXA(2) production, SP (3x10(-10)-3x10(-8) M)-induced EDR was greater in the proximal than distal arteries. Neither contraction induced by U-46619, a TXA(2) agonist, nor relaxation by sodium nitroprusside, an NO donor, was different between both portions of the arteries. Both ionomycin (10(-8) M)- and l-arginine (1 mM)-induced EDRs were also significantly greater in the proximal than distal arteries. Under the blockade of NK(1) receptors and NO and TXA(2) production, SP (10(-7) M)-induced EIC was greater in the distal than proximal arteries. In summary, the capacity for NO production is higher in the proximal than distal arteries, resulting in SP-induced higher EDR and lower EDC in the proximal arteries.

SIGNIFICANCE

These regional differences in responses to SP may play important roles in maintaining the homogenous distribution of blood flow in the lung.

Neurokinins induce relaxation of human pulmonary vessels through stimulation of endothelial NK1 receptors

The effects of neurokinins and neurokinin receptor selective agonists have been investigated on human intralobar pulmonary vessels. Substance P (SP) and [Sar(9) Met(O(2)) ]SP(11), a selective NK(1) receptor agonist, induced concentration-dependent relaxation of pulmonary vessels precontracted with phenylephrine. The mean negative log (M) EC (50) values for SP and [Sar (9) Met(O2))]SP(11) were 8.6 and 8.9, respectively, on arterial preparations and 8.9 and 8.6, respectively, on venous preparations. Relaxations to [Sar(9) Met(O(2) ) ]SP were abolished by the NK receptor antagonist SR140333. The relaxations to a second application of [Sar(9) Met(O (2)) ]SP were markedly reduced, suggesting a rapid desensitization of the NK(1) receptor. Such desensitization was not observed with acetylcholine. The selective NK receptor agonist, [Nle(10)]NKA, and the selective NK (3) receptor agonist, [MePhe(7)]NKB, caused neither contractions nor relaxations of pulmonary vessels. The NK(1) receptor-mediated relaxations were abolished by removing the endothelium or by a combination of -nitro-L-arginine and indomethacin, whereas each compound exerted a partial inhibitory effect. Similar results were observed with acetylcholine. Positive immunostaining for NK(1) receptors was only found in the endothelium. Reverse transcription-polymerase chain reaction detected messenger RNA for NK(1) receptors without any detection of messenger RNA for NK(2) or NK(3) receptors. In conclusion, human pulmonary arteries and veins express endothelial NK(1) receptors that mediate relaxation through a combination of cyclooxygenase and nitric oxide activities and are subjected to rapid tachyphylaxis.

Increased contractile response to 5-hydroxytryptamine1-receptor stimulation in pulmonary arteries from chronic hypoxic rats: role of pharmacological synergy

1. 5-Hydroxytryptamine (5-HT)(1)-receptor-induced contraction is enhanced, or uncovered, by elevated vascular tone in many arteries including pulmonary arteries. In hypoxia-induced pulmonary hypertension, the endogenous tone of pulmonary arteries is elevated and this may contribute to increased 5-HT(1)-receptor-induced contraction. Here we investigate the influence of vascular tone induced by endothelin-1 (ET-1), neuropeptide Y (NPY), KCl, 4-aminopyridine (inactivator of K(v) channels, 4-AP) or the calcium ionophore A23187 on contractile responses to the 5-HT(1)-receptor agonist 5-carboxamidotryptamine (5-CT) in small muscular pulmonary arteries from control rats and rats exposed to chronic hypoxia. The influence of the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM) was also studied. These conditions were chosen to mimic those that influence pulmonary vascular tone in hypoxia-induced pulmonary hypertension. 2. In control rat small pulmonary arteries, only high concentrations of 5-CT (>1 microM) induced vasoconstriction. Tone induced by NPY, 4-AP and A23187 had no effect on responses to 5-CT whilst responses to 5-CT were increased by ET-1- and KCl-induced tone. In the presence of L-NAME these responses to 5-CT were enhanced further. 3. Responses to 5-CT were enhanced 3 - 4 fold in small pulmonary arteries from hypoxia-exposed, pulmonary hypertensive rats and neither L-NAME nor increasing tone with NPY, 4-AP, A23187, ET-1 or KCl had any further effect on responses to 5-CT. 4. The results suggest that inhibition of nitric oxide synthase combined with KCl- or ET-1-induced vascular tone potentiates responses to 5-HT(1)-receptor-induced contraction in pulmonary arteries in a synergistic fashion and this mimics the effects of chronic hypoxic exposure.

Pathobiology of pulmonary hypertension: Impact on clinical management

Our previous studies showed how analysis of pulmonary vascular changes on lung biopsy tissue and on angiography added to the hemodynamic assessment of pulmonary vascular resistance in predicting the success of a surgical repair. Both the potential for heightened vasoreactivity in the early postoperative period and for reversibility of pulmonary vascular disease at later follow-up were correlated with qualitative and quantitative evaluation of arterial changes. The ability of continuous intravenous prostacylin to arrest progression and even induce regression of structurally advanced pulmonary vascular disease in some cases has led to rethinking how pathological material can be useful in clinical decision making. The presence of occlusive changes and particularly plexiform lesions was thought to represent irreversible disease, but the observation that ongoing cellular proliferation and connective tissue synthesis occurs even in advanced lesions thought to represent end stage 'burnt-out' lesions, led to re-evaluation of the potential of biologically reversing the disease process. Our laboratory has used clinical material, cultured cells, and studies in experimental animals to gain new insights into some of the mechanisms which lead to the progression of vascular changes, and has used this information in strategies aimed at arresting progression and, more recently, inducing regression of pulmonary hypertension and associated vascular lesions. Specifically, we have focused on the increased activity of an endogenous vascular elastase (EVE) and expression of the glycoproteins tenascin and fibronectin in the pathobiology of pulmonary hypertension. This report will first review our studies in children with congenital heart defects, assessment of reversibility of pulmonary hypertension, and then discuss more recent work addressing cellular and molecular mechanisms aimed at developing newer therapeutic strategies. Copyright 2000 by W.B. Saunders Company

The development of synaptophysin immunoreactivity in the human sympathetic ganglia

Using an indirect immunohistochemical method, synaptophysin immunoreactivity (SYN-IR) has been studied in cryostat sections of stellate and thoracic ganglia in human fetuses, neonates, infants and adults. In the course of development, a progressive increase in SYN-IR in axonal terminals and around nerve cells was demonstrated. In contrast, large clusters of small intensely fluorescent (SIF) cells and paraganglionic cells increased in number in fetuses and premature neonates at 24-25 weeks. Such SIF cell clusters varied in form and often occurred at pole or subcapsular areas of sympathetic ganglia close to blood vessels or paraganglia. With increasing gestational age and during infancy, a decrease in sizes of SIF cell groups and paraganglionic cells as well as changes in their distribution were found. The results show that the amount and distribution of SYN-IR is temporally related to the maturation and functional activity of human sympathetic ganglia neurons. It was suggested that numerous SIF cells and paraganglia in human prenatal sympathetic ganglia were both indicative of incomplete cell migration and an important source of regulation of ganglionic microcirculation under the conditions of relative hypoxia and immature nervous regulation.

Endothelium-dependent relaxation followed by contraction mediated by NK(1) receptors in precontracted rabbit intrapulmonary arteries

In the present study, we examined whether substance P (SP) and SP methyl ester (SPME), a selective NK(1) agonist, cause biphasic responses consisting of endothelium-dependent relaxation (EDR) and contraction (EDC) in precontracted rabbit intrapulmonary arteries. In arteries contracted with PGF(2alpha) (2x10(-6) M), SP as well as SPME caused only EDR at low concentration (10(-9) M) and EDR followed by EDC at higher concentrations, indicating the involvement of NK(1) receptors. The SP (10(-8) M)-induced EDR was abolished in arteries moderately contracted by PGF(2alpha) (5x10(-7) M) and the EDC in arteries maximally contracted by PGF(2alpha) (10(-5) M), indicating that EDR and EDC are inversely dependent on preexisting tone. Indomethacin (10(-8) - 10(-6) M), a cyclo-oxygenase inhibitor, and ozagrel (10(-8) - 10(-6) M), a TXA(2) synthetase inhibitor attenuated the EDC in the SPME (10(-7) M)-induced biphasic response and markedly potentiated the EDR. AA-861 (10(-8) - 10(-6) M), a 5-lipoxygenase inhibitor, did not affect the EDR or EDC. L-N(G)-nitro-arginine methyl ester (10(-5) - 10(-4) M), a nitric oxide synthase inhibitor, attenuated the EDR and slightly potentiated the EDC. CP-99994 (10(-10) - 10(-8) M), an NK(1) antagonist, attenuated the EDC and potentiated the EDR in the SPME (10(-7) M)-induced biphasic response, while the NK(2) antagonist SR-48968 (10(-9) - 10(-7) M) had no effect. CP-99994 attenuated the SPME (10(-7) M)-induced EDC under EDR-blockade to a greater extent than the EDR under EDC-blockade, indicating that CP-99994 enhanced the EDR component by preferential inhibition of the EDC component. In conclusion, NK(1) agonists caused a biphasic endothelium-dependent response (EDR and EDC) in submaximally precontracted intrapulmonary arteries. The EDC and EDR mediated by NK(1) receptors may play physiological and/or pathophysiological roles in modulation of vascular tone.

Pulmonary hypertension, anorexigens and 5-HT: pharmacological synergism in action?

In pulmonary hypertension (PHT), pulmonary vascular resistance is elevated as a result of increased pulmonary vascular tone and pulmonary vascular remodelling. Certain diet pills, such as the fenfluramines, have been associated with the development of PHT. This class of drugs act as indirect 5-HT receptor agonists and can inhibit 5-HT reuptake and cause the release of 5-HT from platelets. Many pulmonary vasoconstrictors, including 5-HT, activate both Gi- and Gq-linked receptors. Increasing evidence suggests that Gq activation might amplify Gi-linked intracellular pathways to 'uncover' or potentiate vasoconstrictor responses - a phenomenon known as pharmacological synergism, which occurs in the pulmonary circulation. In this review the evidence that 5-HT plays a role in PHT and that pharmacological synergism might contribute to its pathology is discussed.

Resting potentials and potassium currents during development of pulmonary artery smooth muscle cells

The pulmonary circulation changes rapidly at birth to adapt to extrauterine life. The neonate is at high risk of developing pulmonary hypertension, a common cause being perinatal hypoxia. Smooth muscle K+ channels have been implicated in hypoxic pulmonary vasoconstriction in adults and O2-induced vasodilation in the fetus, channel inhibition being thought to promote Ca2+ influx and contraction. We investigated the K+ currents and membrane potentials of pulmonary artery myocytes during development, in normal pigs and pigs exposed for 3 days to hypoxia, either from birth or from 3 days after birth. The main finding is that cells were depolarized at birth and hyperpolarized to the adult level of -40 mV within 3 days. Hypoxia prevented the hyperpolarization when present from birth and reversed it when present from the third postnatal day. The mechanism of hyperpolarization is unclear but may involve a noninactivating, voltage-gated K+ channel. It is not caused by increased Ca2+-activated or delayed rectifier current. These currents were small at birth compared with adults, declined further over the next 2 wk, and were suppressed by exposure to hypoxia from birth. Hyperpolarization could contribute to the fall in pulmonary vascular resistance at birth, whereas the low K+-current density, by enhancing membrane excitability, would contribute to the hyperreactivity of neonatal vessels. Hypoxia may hinder pulmonary artery adaptation by preventing hyperpolarization and suppressing K+ current.

Innervation of nasal turbinate blood vessels in rhinitic and nonrhinitic children

An immunohistochemical study of the nasal mucosa was done in pediatric patients attending an otorhinolaringology (ORL) clinic. The goal was a comparison between vascular innervation in patients with or without symptoms of chronic rhinitis. All patients had an indication for tonsillectomy prior to their inclusion in this study. Samples were obtained under general anesthesia at the time of programmed surgery and fixed in a paraformaldehyde-picric acid mixture. Cryostat sections were immunostained for the following neuronal markers: protein-gene product 9.5 (PGP), calcitonin gene- related peptide (CGRP), substance P (SP), and C-terminal peptide of neuropeptide Y (CPON). The following classes of vessels were identified: arteries, sinusoids, veins, and arteriovenous anastomoses (AVAs). As shown by immunostaining with the general neuronal marker PGP, each vessel type had a characteristic innervation pattern, differing in the amount of fibers and their distribution within the adventitial and muscle layers. Evaluation of PGP, CPON, and CGRP immunoreactivity patterns indicated that rhinitic arteries and AVAs displayed a richer innervation than did nonrhinitic blood vessels. Quantification of vascular PGP immunostaining confirmed the difference of vascular innervation between nonrhinitic and rhinitic patients. Fibers immunostained by CPON partially accounted for the rhinitic arterial hyperinnervation.

Developmental changes in binding sites and reactivity for CGRP and VIP in porcine pulmonary arteries

During postnatal adaptation pulmonary arteries dilate. CGRP and VIP are pulmonary vasodilators. In this report, porcine lungs from newborn to adult were studied. Radiolabeled ligand binding and autoradiography showed CGRP binding sites on the endothelium of pulmonary arteries and veins, which increased postnatally, and VIP binding sites on smooth muscle, which decreased. Isolated conduit arteries relaxed normally (initially endothelium dependent) in response to CGRP from birth. VIP first caused relaxation at 10 days and was endothelium dependent. Age-related changes in receptor binding density were not always reflected in an appropriate alteration in pharmacological response.

Endothelium-dependent contraction in intrapulmonary arteries: mediation by endothelial NK1 receptors and TXA2

1. We have examined whether three natural tachykinins, substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) induce an endothelium-dependent contraction (EDC) in the rabbit isolated intrapulmonary artery. 2. Removal of the endothelium almost abolished the contraction induced by SP (10(-8) M) while it did not attenuate the contraction induced by SP (10(-7) M), NKA (10(-9) - 10(-7) M) or NKB (10(-8) and 10(-7) M). 3. The EDC induced by SP (10(-8) M) was abolished by NK1 antagonists (FK-888, CP-96345, CP-99994 and SR-140333) but not by an NK2 antagonist (SR-48968). 4. The EDC induced by SP was attenuated by cyclo-oxygenase inhibitors (aspirin and indomethacin), thromboxane A2 (TXA2) synthetase inhibitors (OKY-046, KY-234 and KY-063) and a TXA2 antagonist (S-1452). 5. The rank order of potency causing endothelium-independent contraction (EIC) was NKA > NKB > SP. The EIC induced by SP (10(-7) M) was attenuated by an NK2 antagonist but not by NK1 antagonists, cyclo-oxygenase inhibitors, TXA2 synthetase inhibitors or a TXA2 antagonist. 6. In conclusion, SP at 10(-8) M induces EDC via endothelial NK1 receptors and TXA2 production, and SP at 10(-7) M induces EIC via NK2 receptors in the rabbit intrapulmonary artery.

Ultrastructural localization of nitric oxide synthase and endothelin in coronary and pulmonary arteries of newborn rats

This is the first report on the ultrastructural distribution of nitric oxide synthase and endothelin immunoreactivities in the coronary and pulmonary arteries of newborn Wistar rats. The distribution of nitric oxide synthase and endothelin was investigated using pre-embedding peroxidase-antiperoxidase immunocytochemistry. In both arteries examined, positive labelling for nitric oxide synthase was localized both in the endothelium and smooth muscle, whereas positive labelling for endothelin was localized in the endothelium exclusively. In the coronary artery, approximately 80% and 55% of the endothelial cells examined were positive for nitric oxide synthase and endothelin, respectively, whereas in the pulmonary artery, 77% and 60% of the endothelial cells were positive for nitric oxide synthase and endothelin, respectively. These findings indicate that nitric oxide synthase and endothelin are colocalized in some of the endothelial cells of the newborn rat. In the endothelium, nitric oxide synthase and endothelin immunoreactivities were distributed throughout the cell cytoplasm and in association with the membranes of intracellular organelles. In smooth muscle, a relationship of nitric oxide synthase immunoreactivity to endoplasmic reticulum was observed in the pulmonary artery. In summary, in the newborn rat, endothelial cells of the coronary and pulmonary artery are rich in nitric oxide synthase (neuronal isoform) and endothelin, and it is suggested therefore that they may be substantially involved in vasomotor control of the cardiac and pulmonary circulation during early stages of postnatal development.

Distribution of SP- and CGRP-like immunoreactive nerve fibers in the lower respiratory tract of neonatal foals: evidence for loss during development

The lungs of neonatal foals contain many nerves immunoreactive for substance P and calcitonin gene-related peptide. These nerves are closely associated with the epithelium, bronchial and pulmonary vessels and the airway smooth muscle of all intrathoracic airways, including non-cartilaginous bronchioles. Activation of sensory nerves in the respiratory epithelium could thus potentially affect, via local axon reflexes, vascular and respiratory smooth muscle in neonatal equine airways. Nerves immunoreactive for these peptides are much more widely distributed within the lung than in adult horses; they may thus play a trophic role before birth, or contribute to the post-natal adaptation to breathing.

Somatostatin and the lung

Lung carcinoma is the most common cause of death in the western world and is increasing particularly among women. Despite significant developments in our understanding of the molecular biology of this disease our ability to treat the various subtypes of lung cancer has been at a relative standstill for the past decade. Novel approaches to the therapy of lung tumours are required. Recent work has evaluated the potential role of somatostatin and its analogues in the treatment of lung cancer. Experimental evidence has demonstrated that lung tumours, in particular small cell lung cancer (SCLC), may express somatostatin. The significance of this expression has not yet been evaluated. Somatostatin receptors have been demonstrated on between 50-75% of SCLC cell lines and fresh tumour samples studied to date. Using radiolabelled somatostatin analogues SCLC tumours may be detected and localised in patients through scintigraphic imaging techniques. Studies have shown that SCLC cell line clonal proliferation may be inhibited in vitro with somatostatin analogues suggesting that the somatostatin receptors are functional. In-vivo growth inhibition studies have likewise yielded encouraging results with growth inhibition of somatostatin receptor positive SCLC xenografts and receptor negative SCLC and non-small cell lung cancer cell line xenografts. These latter result suggests that somatostatin analogues may inhibit tumour growth by indirect as well as direct means. These findings have laid the ground for formal clinical trials in the future.

Onset and evolution of pulmonary vascular disease in young children: abnormal postnatal remodelling studied in lung biopsies

Pulmonary arterial structure was examined in lung biopsies from 26 children with severe pulmonary hypertensive congenital heart disease, aged 2 months-18 years, in whom the mean pulmonary arterial pressure was 55 (range 35-105) mmHg, using light, transmission, and scanning electron microscopy. Qualitative and quantitative techniques were applied and findings compared with those in age-matched controls. At 2 months, the smooth muscle cells showed hyperplasia, hypertrophy (mean cell diameter increased, P less than 0.001), and accelerated differentiation. In all pulmonary hypertensive cases aged less than 6 months, the contractile myofilament concentration was similar to the normal concentration at 6 months. Medial connective tissue was excessive for age. Smooth muscle cells within the intima (intimal proliferation) were first seen at 7 months, lying beneath a new internal elastic lamina. They showed a reduction in myofilament concentration in the more fibrotic lesions. In all cases, endothelial cells were abnormally thick (P less than 0.001) and elongated. Cytoskeletal remodelling was indicated by an increase in micro- and intermediate filament volume density (P less than 0.05 for both). The severity of endothelial damage was related to vessel size and position in the arterial pathway. These findings indicate that pulmonary vascular disease begins at or soon after birth with abnormal pulmonary vascular remodelling which leads to obliterative pulmonary vascular disease.

Fatal persistent pulmonary hypertension presenting late in the neonatal period

Two cases of fatal idiopathic persistent pulmonary hypertension presented late in the neonatal period. Lungs were examined histologically by light and electron microscopy, and immunocytochemical studies were used to identify nerves. There was extension of medial smooth muscle distally along the arterial pathway so that most precapillary arteries had completely muscular walls, which in some cases completely obliterated the vessel lumen. Enlarged endothelial cells also contributed to the reduction in the size of the lumen. Nerve fibres accompanying muscular arteries were found in the alveolar region, more distal than is normal. The predominant neuropeptide was the vasoconstrictor tyrosine. Possible aetiological factors in persistent pulmonary hypertension of the newborn are increased muscularity of the peripheral pulmonary arteries antenatally, an increase in the number of vasoconstrictor nerves, or an imbalance in the production of leukotrienes and prostacyclins in the perinatal period.