Contractile responses and structure of small bronchi isolated from rats after 20 months' exposure to ozone

Short-term exposure to high concentrations of ozone has been shown to increase airway responsiveness in normal humans and in all laboratory animal species studied to date. While our knowledge concerning the pulmonary effects of single exposures to ozone has increased rapidly over recent years, the effects of repeated exposures are less understood. The goal of the present study was to determine whether airway responsiveness is increased after near-lifetime exposure to ozone. Airway segments representing approximately eighth generation airways were isolated from Fischer 344 rats of both genders that had been exposed for 6 hr per day, 5 days per week for 20 months to 0, 0.12, 0.5, or 1.0 parts per million (ppm) ozone. Circumferential tension development was measured in isolated airways in response to bethanechol, acetylcholine, and electrical field stimulation. Responsiveness of the airways to the contractile stimuli was described by the effective dose or frequency that elicited half-maximum contraction (ED50) and the maximum response. Since ozone exposure is associated with remodeling of peripheral airways, smooth muscle area was determined and tension responses were normalized to the area measurements. Before normalization of tension data to smooth muscle area, neither the ED50 nor maximum response of small bronchi to the contractile stimuli was altered after chronic ozone exposure. Smooth muscle area was greater in airways isolated from animals that had been exposed to 0.5 ppm ozone. After accounting for smooth muscle area, maximum responses of the small bronchi isolated from male rats were significantly reduced after 0.12 and 0.5 ppm ozone. Although not significant statistically, a similar trend was observed in airways isolated from female rats. These results suggest that the increase in airway responsiveness associated with acute ozone exposure does not persist during near-lifetime exposure. Although the mechanism responsible for the adaptation to the effects of O3 on airway responsiveness is unknown, the results indicate that smooth muscle cell function was compromised by the chronic exposure. The mechanism(s) responsible for mediating this effect and the relevance of these results to humans remains to be determined.     

Effects of bronchial vascular engorgement on airway dimensions

Airway vascular engorgement has been suggested to cause luminal narrowing and airflow obstruction. To determine the extent to which changes in bronchial vascular volume could influence airway dimensions, we studied the effects of left atrial pressure elevation on airway morphometry in sheep (n = 17). The bronchial branch of the bronchoesophageal artery was cannulated and perfused with autologous blood (0.6 ml.min-1.kg-1). A balloon-tipped catheter was inserted into the left atrial appendage to elevate left atrial pressure by 10 mmHg, and papaverine was infused into the bronchial artery to eliminate airway smooth muscle tone. Morphological measurements were made from rapidly frozen lungs excised in vivo. Left atrial pressure elevation caused a 79% increase in total vascular area (P = 0.0002). Average airway luminal area was significantly decreased from 86 to 71% of the airway maximal area (P < 0.0001). Noteworthy were the prominent bronchial vessels located within mucosal folds. However, when papaverine was infused during left atrial pressure elevation, despite a comparable total vascular area, luminal narrowing did not occur and remained at 87% of the maximal area (P = 0.6267). In conclusion, we found that engorgement of the bronchial vasculature leads to an increase in the vascular area in regions inside and outside the smooth muscle layer. The associated decrease in luminal area only occurs in the presence of airway smooth muscle tone. This suggests a reflex effect on the airway caused by the vascular engorgement. We conclude that vascular engorgement of the airway wall per se has a negligible effect on airway obstruction.     

A comparison of sensory nerve function in human, guinea-pig, rabbit and marmoset airways

We have investigated the role of sensory nerves in regulating airway smooth muscle function in the guinea-pig, marmoset, rabbit and man. Tissue levels of the sensory neuropeptides CGRP and substance P in the airways of the guinea-pig were significantly greater compared with the rabbit and marmoset. The relative order of tissue content was guinea-pig > rabbit = marmoset. Marmoset bronchial and tracheal preparations responded weakly to exogenously administered substance P and neurokinin A but contracted to methacholine and demonstrated atropine-sensitive cholinergic responses. In marmoset, rabbit and human airway preparations, capsaicin mediated weak contractile responses to exogenously administered capsaicin. However, high concentrations of capsaicin elicited a relaxation response that was epithelium-independent, cyclo-oxygenase-insensitive, not involving nitric oxide and not dependent on the activation of capsaicin-sensitive afferents. These results suggest that rabbit and marmoset airways respond functionally in a similar way to human airway preparations and maybe more relevant than guinea-pig airways with regard to understanding the role of sensory neuropeptides in airways.     

Regulation of GLUT1 in response to cellular stress

We assessed the effect of smooth muscle contraction and relaxation on airway lumen subtended by the internal perimeter (Ai) and total cross-sectional area (Ao) of human bronchial explants in the absence of the potential lung tethering forces of alveolar tissue to test the hypothesis that bronchoconstriction results in a comparable change of Ai and Ao. Luminal area (i.e., Ai) and Ao were measured by using computerized videomicrometry, and bronchial wall area was calculated accordingly. Images on videotape were captured; areas were outlined, and data were expressed as internal pixel number by using imaging software. Bronchial rings were dissected in 1.0- to 1.5-mm sections from macroscopically unaffected areas of lungs from patients undergoing resection for carcinoma, placed in microplate wells containing buffered saline, and allowed to equilibrate for 1 h. Baseline, Ao [5.21 +/- 0.354 (SE) mm2], and Ai (0.604 +/- 0.057 mm2) were measured before contraction of the airway smooth muscle (ASM) with carbachol. Mean Ai narrowed by 0.257 +/- 0.052 mm2 in response to 10 microM carbachol (P = 0.001 vs. baseline). Similarly, Ao narrowed by 0.272 +/- 0.110 mm2 in response to carbachol (P = 0.038 vs. baseline; P = 0.849 vs. change in Ai). Similar parallel changes in cross-sectional area for Ai and Ao were observed for relaxation of ASM from inherent tone of other bronchial rings in response to 10 microM isoproterenol. We demonstrate a unique characteristic of human ASM; i.e., both luminal and total cross-sectional area of human airways change similarly on contraction and relaxation in vitro, resulting in a conservation of bronchiolar wall area with bronchoconstriction and dilation.     

Helospectin/helodermin-like peptides in guinea pig lung: distribution and dilatory effects

The lower airways of guinea pigs were analysed for helospectin and helodermin using immunocytochemistry. A moderate supply of helospectin/helodermin-like immunoreactive nerve fibers and few nerve fibers displaying helodermin immunoreactivity was seen in the smooth muscle, around seromucous glands and small blood vessels in the trachea and around bronchi and pulmonary blood vessels. Helospectin I-, helospectin II- and helodermin-induced suppression of smooth muscle responses were analysed using isolated circular segments of trachea and pulmonary arteries of guinea pigs. In both airways and arteries the peptides caused a concentration-dependent relaxation of precontracted segments. The maximal relaxant activity observed was more pronounced in the airways than in the arteries. The effects of the helospectins and helodermin were compared to those of vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI), pituitary adenylate cyclase activating peptide (PACAP) and acetylcholine (ACh). All peptides, with the exception of PACAP, caused a total or nearly total relaxation of the precontracted tracheal segments. In the trachea PACAP was significantly more potent than the other five peptides whereas only small potency differences were seen in the pulmonary artery. The relaxant responses to helospectin I, helospectin II and helodermin in the trachea and the intrapulmonary arteries were unaffected by pretreatment with atropine, prazosin, yohimbine, propranolol, mepyramine and cimetidine. Conceivably, nerve fibers containing helospectin and helodermin may play a role in the regulation of airway resistance and in the regulation of local pulmonary blood flow.     

Measurement of maxillary sinus volume using computerized tomographic images

We have investigated the effects of L-arginine, D-arginine and L-lysine on airway smooth muscle responsiveness to spasmogens in vitro. Both L-arginine and D-arginine (100 mM) significantly reduced the contractile potency and maximal contractile response to histamine but not to methacholine or potassium chloride in guinea-pig epithelium-denuded isolated trachea. Similarly, the contractile response to histamine was significantly reduced by L-arginine (100 mM) in rabbit epithelium-denuded isolated bronchus. The amino acid L-lysine (100 mM) failed to significantly alter the contractile potency of histamine in guinea-pig isolated trachea (P > 0.05). In guinea-pig isolated trachea precontracted with histamine, both L-arginine and D-arginine produced a concentration-dependent relaxation which was not significantly altered by epithelium removal or by the presence of the nitric oxide synthase inhibitor, NG-nitro L-arginine methyl ester (L-NAME; 50 microM). Thus, at very high concentrations, arginine exhibit a non-competitive antagonism of histamine-induced contraction of isolated airway preparations that was independent of the generation of nitric oxide and was not dependent on charge. These observations confirm previous studies of cutaneous permeability responses and of contractile responses of guinea-pig isolated ileal smooth muscle. Taken together, the data suggest that high concentrations of arginine can exert an anti-histamine effect.     

Inflammatory cell distribution within and along asthmatic airways

Asthmatic airways are infiltrated with inflammatory cells that release mediators and cytokines into the microenvironment. In this study, we evaluated the distribution of CD45-positive leukocytes and eosinophils in lung tissue from five patients who died with severe asthma compared with five patients with cystic fibrosis. For morphometric analysis, the airway wall was partitioned into an "inner" area (between basement membrane and smooth muscle) and an "outer" area (between smooth muscle and alveolar attachments). Large airways (with a perimeter greater than 3.0 mm) from patients with asthma or cystic fibrosis had a greater density of CD45-positive cells (p < 0.05) and eosinophils (p < 0.001) in the inner airway region compared with the same airway region in small airways. Furthermore, in small airways, asthmatic lungs showed a greater density of CD45-positive cells (p < 0.01) and eosinophils (p < 0.01) in the outer compared with the inner airway wall region. These observations indicate that there are regional variations in inflammatory cell distribution within the airway wall in patients with asthma that are not observed in airways from patients with cystic fibrosis. We speculate that this inflammatory cell density in peripheral airways in severe asthma may relate to the peripheral airway obstruction characteristic of this condition.     

Mechanism of cytokine-induced modulation of beta-adrenoceptor responsiveness in airway smooth muscle

To elucidate the role of specific proinflammatory cytokines in regulating airway responsiveness, we examined the effects and mechanisms of action of IL-1beta, TNF-alpha, and IL-2 on the beta-adrenoceptor- and postreceptor-coupled transmembrane signaling mechanisms regulating relaxation in isolated rabbit tracheal smooth muscle (TSM) segments. During half-maximal isometric contraction of the tissues with acetylcholine, relaxation responses to isoproterenol, PGE2, and forskolin were separately compared in control (untreated) TSM and tissues incubated for 18 h with IL-1beta (10 ng/ml), TNF-(alpha (100 ng/ml), or IL-2 (200 ng/ml). Relative to controls, IL-1beta- and TNF-alpha-treated TSM, but not IL-2-treated tissues, depicted significant attenuation of their maximal relaxation and sensitivity (i.e., -log dose producing 50% maximal relaxation) to isoproterenol (P < 0.001) and PGE2 (P < 0.05); whereas the relaxation responses to direct stimulation of adenylate cyclase with forskolin were similar in the control and cytokine-treated tissues. Further, the attenuated relaxation to isoproterenol and PGE2 was ablated in the IL-1beta-treated TSM that were pretreated with either the muscarinic M2-receptor antagonist, methoctramine (10(-6) M), or pertussis toxin (100 ng/ml). Moreover, Western immunoblot analysis demonstrated that: (a) Gi protein expression was significantly enhanced in membrane fractions isolated from IL-1beta-treated TSM; and (b) the latter was largely attributed to induced enhanced expression of the Gi alpha2 and Gi alpha3 subunits. Collectively, these observations provide new evidence demonstrating that IL-lbeta and TNF-alpha induce impaired receptor-coupled airway relaxation in naive TSM, and that the latter effect is associated with increased muscarinic M2-receptor/Gi protein-coupled expression and function.     

Beta-adrenoceptors on smooth muscle, nerves and inflammatory cells

Although the bronchodilator action of beta 2-adrenoceptor agonists in asthma is largely due to relaxation of airway smooth muscle, these agents have other effects which may contribute to their anti-asthma action. Human airway smooth muscle contains only beta 2-receptors which, when stimulated, stimulate a rise in intracellular cAMP and activation of PKA (protein kinase A), which in turn phosphorylates several cellular proteins, resulting in relaxation. However, beta-agonists also influence membrane K+ channels and induce smooth muscle relaxation without a rise in cAMP, and this mechanism appears to be the major feature of bronchodilatation in asthma. There is also evidence that beta-agonists may modulate neurotransmission in airways via prejunctional receptors on airway nerves, both sensory and motor. Blockade of prejunctional beta 2-receptors in asthma patients may lead to marked rise in acetylcholine release, with severe bronchoconstriction. Although beta-agonists have little or no effect on the chronic inflammatory response which underlies chronic airway hyper-responsiveness, they do inhibit the release of histamine from mast cells in vitro. The presence of beta-receptors has also been detected not only on mast cells but also on eosinophils, macrophages, lymphocytes and neutrophils, but beta-agonists have little or no inhibitory action on the activities of all these cells due to rapid tachyphylaxis.     

Evidence that different mechanisms underlie smooth muscle relaxation to nitric oxide and nitric oxide donors in the rabbit isolated carotid artery

1. The endothelium-dependent relaxants acetylcholine (ACh; 0.03-10 microM) and A23187 (0.03-10 microM), and nitric oxide (NO), applied either as authentic NO (0.01-10 microM) or as the NO donors 3-morpholino-sydnonimine (SIN-1; 0.1-10 microM) and S-nitroso-N-acetylpenicillamine (SNAP; 0.1-10 microM), each evoked concentration-dependent relaxation in phenylephrine stimulated (1-3 microM; mean contraction and depolarization, 45.8+/-5.3 mV and 31.5+/-3.3 mN; n=10) segments of rabbit isolated carotid artery. In each case, relaxation closely correlated with repolarization of the smooth muscle membrane potential and stimulated a maximal reversal of around 95% and 98% of the phenylephrine-induced depolarization and contraction, respectively. 2. In tissues stimulated with 30 mM KCl rather than phenylephrine, smooth muscle hyperpolarization and relaxation to ACh, A23187, authentic NO and the NO donors were dissociated. Whereas the hyperpolarization was reduced by 75-80% to around a total of 10 mV, relaxation was only inhibited by 35% (n=4-7 in each case; P<0.01). The responses which persisted to ACh and A23187 in the presence of 30 mM KCl were abolished by either the NO synthase inhibitor L-NG-nitroarginine methyl ester (L-NAME; 100 microM) or the inhibitor of soluble guanylyl cyclase 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 microM; 10 min; n=4 in each case; P<0.01). 3. Exposure to ODQ significantly attenuated both repolarization and relaxation to ACh, A23187 and authentic NO, reducing the maximum changes in both membrane potential and tension to each relaxant to around 60% of control values (n=4 in each case; P<0.01). In contrast, ODQ almost completely inhibited repolarization and relaxation to SIN-1 and SNAP, reducing the maximum responses to around 8% in each case (n=3-5; P<0.01). 4. The potassium channel blockers glibenclamide (10 microM), iberiotoxin (100 nM) and apamin (50 nM), alone or in combination, had no significant effect on relaxation to ACh, A23187, authentic NO, or the NO donors SIN-1 and SNAP (n=4 in each case; P>0.05). Charybdotoxin (ChTX; 50 nM) almost abolished repolarization to ACh (n=4; P<0.01) and inhibited the maximum relaxation to ACh, A23187 and authentic NO each by 30% (n=4-8; P<0.01). Application of ODQ (10 microM; 10 min) abolished the ChTX-insensitive responses to ACh, A23187 and authentic NO (n=4 in each case; P<0.01 5. When the concentration of phenylephrine was reduced (to 0.3-0.5 microM) to ensure the level of smooth muscle contraction was the same as in the absence of potassium channel blocker, ChTX had no effect on the subsequent relaxation to SIN-1 (n=4; P>0.05). However, in the presence of tone induced by 1-3 microM phenylephrine (51.2+/-3.3 mN; n=4), ChTX significantly reduced relaxation to SIN-1 by nearly 50% (maximum relaxation 53.2+/-6.3%, n=4; P<0.01). 6. These data indicate that NO-evoked relaxation of the rabbit isolated carotid artery can be mediated by three distinct mechanisms: (a) a cyclic GMP-dependent, voltage-independent pathway, (b) cyclic GMP-mediated smooth muscle repolarization and (c) cyclic GMP-independent, ChTX-sensitive smooth muscle repolarization. Relaxation and repolarization to both authentic and endothelium-derived NO in this large conduit artery appear to be mediated by parallel cyclic GMP-dependent and -independent pathways. In contrast, relaxation to the NO-donors SIN-1 and SNAP appears to be mediated entirely via cyclic GMP-dependent mechanisms.     

Time-course of functional and pathological changes after a single high acute inhalation of chlorine in rats

Reactive airways dysfunction syndrome (RADS) is an asthma-like condition that follows exposure to very high concentrations of an irritant material. We assessed the time-course of pathophysiological alterations in a model of RADS. Sprague-Dawley rats were exposed to 1,500 parts per million (ppm) of chlorine for 5 min. Lung resistance (RL), responsiveness to inhaled methacholine (MCh), the airway epithelium and bronchoalveolar lavage (BAL) were assessed over a 3 month period after exposure. RL increased significantly up to 3 days after exposure, reaching a maximal change of 110+/-16% from baseline. There was a significant decrease in the concentration of MCh required to increase RL by 0.20 cmH2O x mL(-1) x s from days 1-7 after exposure. In some rats, MCh hyperresponsiveness and RL changes persisted after exposure for as long as 1 and 3 months, respectively. Histological evaluation with morphometric evaluation revealed epithelial flattening, necrosis, increase in smooth muscle mass and evidence of epithelial regeneration. BAL showed an increased number of neutrophils. The timing of maximal abnormality in the appearance of the epithelium (days 1-3) corresponded to that of the maximal functional changes. Acute high chlorine exposure results in functional and pathological abnormalities that resolve in the majority of animals after a variable period; however, these changes can persist in some animals. Functional abnormalities in the initial stages may be related to airway epithelial damage.     

Dibutyryl cGMP raises cytosolic concentrations of Ca2+ in cultured nodose ganglion neurons of the rabbit

Airway hyperresponsiveness in asthma has been attributed to impaired ability of deep inspiration (DI) to stretch airway smooth muscle. We have retested this hypothesis by comparing the responses to methacholine of 10 asthmatic and 10 control subjects. After each dose subjects breathed tidally without deep inspiration for 4 min, followed by a forced partial expiration from which flow was measured at a constant volume, 35% baseline VC (Vp 35). This index is independent of both DI and increases in end-inspiratory lung volume (EILV). EILV increased significantly more in the asthmatic group than in the control group (15.0 versus 2.5% of baseline VC, p = 0. 019), a factor that if not taken into account would tend to mask the difference in the two responses. Comparisons were made after a cumulative dose of 50 microg methacholine, which was the highest dose common to all subjects. The asthmatic response was significantly greater than that seen in the control group, with reductions to 25.9 and 72.1% of baseline Vp 35, respectively (p = 0. 0007). We conclude that the sensitivity of asthmatic airways to methacholine is greater than that of normal airways even when DI is prohibited. Therefore, the hyperresponsiveness of asthmatic airways is not attributable simply to an inability of DI to stretch airway smooth muscle.     

Identification and semi-quantitation of Ostertagia ostertagi eggs by enzymatic amplification of ITS-1 sequences

The forced oscillation technique (FOT) is a non-invasive method which may be suitable for assessing upper airway obstruction in obstructive sleep apnea/hypopnea syndrome (OSAS) patients. The aim of this study was to determine in vitro if FOT can provide an early detection index of total or partial upper airway occlusion. A respiratory system analog was developed which includes an upper airway analog that allows simulation of upper airway collapse (thus mimicking the situation in patients with OSAS). We simulated different degrees of upper airway obstructions ranging from 0 (unobstructed airways) to 1 (total occlusion). Furthermore, we imitated the collapsible upper airway wall by means of elastic membranes with ten different wall compliances ranging from 3.3 x 10(-4) to 1 1/mbar. For the two stiffest rubber membranes (Cwall = 0.01 and 3.3 x 10(-4) l/mbar) the absolute value of the impedance (?Z?) showed a marked increase for obstructions greater than 0.6. For the two membranes with the highest wall compliances (Cwall = 0.03 and 1 1/mbar) obstructions with an increase in ?Z? could not be detected before the obstruction reached 0.8. For degrees of obstruction less than 0.6 the phase angle of collapsible membranes with low compliance (stiff airway wall) were about 1.5pi which significantly differed from phase angles of 1.77pi measured in membranes with high compliance (elastic airway wall); p < 0.01. We hypothesized that stiffness of upper airway walls corresponds with their muscle tone, i.e., stiff airway walls are related with high muscle tone and vice versa. Thus, a decrease in upper airway muscle activity would cause an increase of upper airway wall elasticity that enables upper airway collapse. As a consequence the phase angle phi could be expected to change from values characterizing stiff membranes to values characterizing more elastic membranes which could be used as early indicator for obstructive respiratory events. We have frequently observed such changes in morphology of phi(t) data obtained from patients with OSAS.     

Airway epithelium: more than just a barrier!

Airway hyper-responsiveness and epithelial cell damage are associated commonly with asthma. The airway epithelium is a physical barrier that protects sensory nerves and smooth muscle from stimulation by inhaled irritants. In addition, epithelial cells release mediators that can inhibit bronchoconstriction by relaxing the underlying smooth muscle: so-called 'epithelium-derived relaxing factors' (EpiDRFs). Clear functional evidence for EpiDRFs is provided by experiments where different endogenous mediators induce the relaxation of tracheas containing epithelium, but cause a contraction in preparations lacking this layer. Here, Gert Folkerts and Frans Nijkamp describe the pharmacological relevance of the putative EpiDRFs, prostaglandin E2 and NO, in the modulation of airway tone under basal conditions in vitro and in vivo. Special attention is paid to the role of both EpiDRFs in the development of airway hyper-responsiveness in animal models and in patients with asthma.     

Muscarinic receptor subtypes in the porcine lung during postnatal development

The responsiveness of the pulmonary circulation to acetylcholine changes in the newborn piglet. Therefore muscarinic receptors have been studied in the developing porcine lung from birth to adulthood using ligand binding, Northern blotting and in situ hybridisation. Maximal binding capacity of [N-methyl-3H] scopolamine and the affinity of the receptor in lung membranes increased between birth and 16 days (p < 0.05). Subtype affinity changed with age, but always M3, > M1 > M2. Northern blots of porcine muscarinic receptor subtypes showed m1, m2 and m3 mRNA present in lung membranes. m2 mRNA was present at all ages and decreased with age. m1 mRNA was absent at birth and m3 mRNA was absent at 3 days. Autoradiographic localisation showed ligand binding to the parenchyma and airway smooth muscle and nerves, there was no binding to intrapulmonary vessels. In situ hybridisation localised mRNA of all three subtypes to the smooth muscle cells of both vessels and airways. Changes in the receptor subtypes may explain the pharmacological changes during postnatal adaptation.     

L-arginine deficiency causes suppression of nonadrenergic noncholinergic nerve-mediated smooth muscle relaxation: role of L-citrulline recycling

Studies were performed on the internal anal sphincter (IAS) smooth muscle strips obtained from opossums (Didelphis virginiana). Isometric tension and L-arginine levels of the tissues were measured under basal conditions, in the presence of electrical field stimulation (EFS) and after treatment with different concentrations of arginase. For the nonadrenergic noncholinergic nerve stimulation, short trains (4 sec) as well as continuous EFS were used. During continuous EFS, after the initial IAS relaxation, the response began to fade within several min to approximately 80% recovery of the basal tone. We also examined the influence of L-arginine and L-citrulline on these responses. For some studies, the tissues were pretreated with L-glutamine (an inhibitor of L-citrulline uptake), L-glutamate or N(G)-hydroxy-L-arginine (an inhibitor of arginase). Interestingly, the basal levels of L-arginine were found to be significantly higher in the IAS (tonic smooth muscle) than in the rectal (phasic smooth muscle) smooth muscle. Arginase caused a concentration-dependent attenuation of the IAS relaxation caused by EFS. L-Citrulline and L-arginine were equipotent in reversing the attenuation. Both arginase (60 min pretreatment) and continuous EFS (tissues collected at the time of maximal recovery of the basal IAS tone after the initial relaxation) caused significant decreases in L-arginine levels. The decreases in the levels of L-arginine were restored by the exogenous administration of either L-arginine or L-citrulline. The restoration of L-arginine levels by L-citrulline but not by L-arginine was selectively blocked by L-glutamine. Furthermore, the IAS relaxation, attenuated by arginase was unaffected by L-glutamine but was restored by N-hydroxy-L-arginine pretreatment. The studies suggest that L-citrulline-L-arginine recycling may play a significant role in the maintenance of IAS relaxation in response to nonadrenergic noncholinergic nerve stimulation.     

Outcome of pulmonary vascular disease in pregnancy: a systematic overview from 1978 through 1996

OBJECTIVES: Published reports were reviewed to evaluate the characteristics of peripartal management and the late pregnancy outcome in women with pulmonary vascular disease (PVD). BACKGROUND: Pulmonary hypertension poses one of the highest risks for maternal mortality, but actual data on the maternal and neonatal prognosis in this group are lacking. METHODS: Reports published from 1978 through 1996 of Eisenmenger's syndrome (n = 73), primary pulmonary hypertension (PPH) (n = 27) and secondary vascular pulmonary hypertension (SVPH) (n = 25) complicating late pregnancy were included and analyzed using logistic regression analysis. RESULTS: Maternal mortality was 36% in Eisenmenger's syndrome, 30% in PPH and 56% (p < 0.08 vs. other two groups) in SVPH. Except for three prepartal deaths due to Eisenmenger's syndrome, all fatalities occurred within 35 days after delivery. Neonatal survival ranging from 87% to 89% was similar in the three groups. Previous pregnancies, timing of the diagnosis and hospital admission, operative delivery and diastolic pulmonary artery pressure were significant univariate (p < 0.05) maternal risk factors. Late diagnosis (p = 0.002, odds ratio 5.4) and late hospital admission (p = 0.01, odds ratio 1.1 per week of pregnancy) were independent predictive risk factors of maternal mortality. CONCLUSIONS: In the last two decades maternal mortality was comparable in patients with Eisenmenger's syndrome and PPH; however, it was relevantly higher in SVPH. Maternal prognosis depends on the early diagnosis of PVD, early hospital admission, individually tailored treatment during pregnancy and medical therapy and care focused on the postpartal period.     

Inhibitory nerve distribution and mediation of NANC relaxation by nitric oxide in horse airways

The distribution of inhibitory nerves and the mediator of the inhibitory nonadrenergic noncholinergic (iN-ANC) nervous system were investigated in smooth muscle preparations from seven regions of equine airways. In tissues incubated with atropine and precontracted with histamine, electrical field stimulation produced frequency-dependent relaxation, and the magnitude of the relaxation decreased from trachea to central bronchi and was absent in peripheral airways. The degree of relaxation in bronchi was not simply a function of bronchial size or generation. Propranolol inhibited part of the relaxation only in the cranial trachealis. After propranolol, NG-nitro-L-arginine, a nitric oxide (NO) synthase inhibitor, eliminated the remaining relaxation in all preparations. This effect was reversed by L-arginine, the NO precursor, but not by D-arginine. Exogenous NO concentration dependently relaxed trachealis. These results indicate that: 1) adrenergic innervation is limited to cranial trachealis, 2) iNANC nerves supply the trachea and central bronchi, and 3) NO mediates iNANC function.     

Histamine-induced contraction of human isolated bronchus is enhanced by endogenous prostaglandin F2 alpha and activation of TP receptors

The effect of histamine on the production of prostaglandin F2 alpha and the actions of prostaglandin F2 alpha on the responsiveness of human isolated bronchial smooth muscle were examined by organ bath techniques using bronchi from lung tissue resected from 18 patients. Following exposure to histamine, epithelium-intact bronchi generated 34.26 +/- 16.3 pg of prostaglandin F2 alpha/mg of tissue and epithelium-denuded preparations produced 32.62 +/- 11.83 pg/mg, suggesting that histamine-induced release of prostaglandin F2 alpha was from non-epithelial sources, presumably smooth muscle. The histamine H2 receptor antagonist ranitidine did not affect the release of prostaglandin F2 alpha, suggesting that its generation may have resulted from histamine H1 receptor activation. Carbachol did not influence prostaglandin F2 alpha generation. Contractile responses to histamine, prostaglandin F2 alpha and carbachol were measured in the presence and absence of the prostaglandin TP receptor antagonist SQ 29,548 ([1 S-[1 alpha,2 beta(5Z),3 beta,4 alpha]]-7-[3[[2-[9-phenylamino)carbonyl]hydrazino] methyl-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid) (0.4 microM). SQ 29,548 abolished responses to prostaglandin F2 alpha suggesting that contractions were mediated via TP receptors. Exposure to SQ 29,548 also produced a 3-fold rightward shift in the concentration-effect curve for histamine (P = 0.01) without influencing the maximum response. SQ 29,548 did not affect responses to carbachol. These results suggest that histamine selectively stimulates the generation of prostaglandin F2 alpha from epithelium-denuded human airway tissue (presumably from the smooth muscle), which in turn, amplifies the contractile responses of human airway smooth muscle to histamine.     

Cerebrovascular relaxation responses to endothelium-dependent and -independent vasodilators after normothermic and hypothermic cardiopulmonary bypass in the rabbit

BACKGROUND: Cardiopulmonary bypass causes activation of leukocytes and increased concentrations of proinflammatory mediators, which may result in endothelial dysfunction. Because hypothermia attenuates many inflammatory processes, the authors hypothesized that hypothermic cardiopulmonary bypass would be associated with better endothelial function than normothermic cardiopulmonary bypass. METHODS: Isoflurane-anesthetized New Zealand White rabbits were randomized to undergo 90 min of either normothermic (37 degrees C, n=9) or hypothermic (27 degrees C, n=9) cardiopulmonary bypass with terminal rewarming. A third group served as anesthetized normothermic non-cardiopulmonary bypass surgical controls (n=8). Basilar artery and descending thoracic aorta were isolated from each animal. In vitro vessel relaxation responses to increasing concentrations of acetylcholine (which induces endothelial release of nitric oxide) and nitroprusside (which provides exogenous nitric oxide) were measured in phenylephrine-precontracted vessel rings. RESULTS: There were no differences in vessel relaxation responses between normothermic and hypothermic cardiopulmonary bypass groups in basilar artery or aorta. In contrast, basilar arteries from non-cardiopulmonary bypass controls had increased relaxation responses to both acetylcholine (P=0.004) and nitroprusside (P=0.031) compared with the pooled cardiopulmonary bypass animal data. CONCLUSIONS: The authors observed no differences in endothelial or vascular smooth muscle function between normothermic and hypothermic cardiopulmonary bypass groups. Compared with non-cardiopulmonary bypass controls, cardiopulmonary bypass appeared to decrease basilar artery smooth muscle relaxation in response to endogenous and exogenous nitric oxide.