Protection against methacholine bronchoconstriction to assess relative potency of inhaled beta2-agonist.

The purposes of this study were to estimate the relative dose potency (RP) of two formulations of salbutamol pressurized metered-dose inhalers (Proventil-HFA and Ventolin-CFC MDIs) to protect against methacholine bronchoconstriction, to validate this method and provide recommendations. The protective effects of 100-, 200-, and 400-micrograms doses of Proventil-HFA were compared with the same doses of Ventolin-CFC in 18 adult asthmatics (mean FEV1, 92% predicted; mean baseline PC20 methacholine, 1.8 mg/ml), in a dose-level blind, balanced, eight-period, crossover, placebo-controlled study. The log-transformed PC20 values after each dose of the drugs were compared by repeated-measures analysis of variance (ANOVA). A significant dose-effect was present (p < 0.0001). Using the Finney assay, the RP of Proventil-HFA compared with Ventolin-CFC was 1.08 (90% CI, 0.81-1.46) (80% power). This was also estimated using a nonlinear Emax model to validate the Finney method. The most precise estimate of RP was obtained with the comparison between 100- and 200-micrograms doses (RP, 1.00; 90% CI, 0.77-1.31). There were no adverse events resulting from the drugs or methacholine. We conclude that Proventil-HFA salbutamol is bioequivalent to Ventolin-CFC salbutamol. Bronchoprotection to methacholine is a valid method of demonstrating bioequivalence. By this method, 100- and 200-micrograms doses of salbutamol inhalations from an MDI will suffice.     

The influence of pretreatment with prostaglandin F2 alpha on bronchial sensitivity to inhaled histamine and methacholine in normal subjects

The effect of pretreatment with prostaglandin F2 alpha (PGF2 alpha) on the bronchial sensitivity to histamine and methacholine has been studied in three groups of six normal subjects, and compared with the effect of citric acid aerosol as a non-specific stimulant of bronchial irritant receptors. Aerosols were generated by Wright's nebulizer and dose-response curves to histamine and methacholine constructed following preadministration of saline, prostaglandin F2 alpha or citric acid. Following prostaglandin F2 alpha pretreatment, the PC20 histamine fell from 12.9 mg/ml to 3.4 mg/ml (P less than 0.01), but the PC20 methacholine was unchanged. Citric acid was without effect. The results indicate that prostaglandin F2 alpha can increase bronchial sensitivity to inhaled histamine, possibly via a direct effect on the airway smooth muscle.     

C-reactive protein-mediated phagocytosis of Leishmania donovani promastigotes does not alter parasite survival or macrophage responses

C-reactive protein (CRP) is an acute phase protein that binds to surface structures of a number of different organisms. Leishmania donovani express CRP ligand when first entering the mammalian host and CRP has been shown to alter macrophage function. The aim of this study was to investigate the functional significance of CRP-mediated uptake of L. donovani on survival of the parasite within human macrophages and macrophage cell responses to the infection. CRP opsonized L. donovani uptake was inhibitable by including excess CRP in the fluid phase, suggesting Fc receptor usage rather than indirect complement-mediated uptake. Comparing equivalent initial infection loads, parasite survival over 72 h within peripheral blood derived macrophages (PBMs) and differentiated U937 cells was unaltered by CRP. Whereas CRP increased macrophage responses to phosphorylcholine coated erythrocytes, no significant alteration in tumour necrosis factor-alpha, interleukin (IL)-10 or IL-12 production from PBMs was observed between CRP opsonized or unopsonized L. donovani promastigotes. Thus, in contrast to other systems, where CRP opsonization results in macrophage activation, Leishmania can use CRP to improve infection without inducing detrimental macrophage activation.     

Acute exposure to sawdust does not alter airway calibre and responsiveness to histamine in asthmatic subjects

We investigated the effects of particles of sawdust delivered through a special device at known concentrations (close to the threshold limit value-short term exposure limit (TLV-STEL) of 10 mg.m-3) on FEV1 and PC20 in 12 asthmatic subjects free of clinical sensitization to this product. Subjects were studied over two days (day 1: exposure to sawdust; day 2: sham exposure) in random order with a maximum interval of 1 week. On each day, after the assessment of spirometry and PC20, subjects underwent exposure to sawdust or sham exposure. Sawdust was inhaled for a total of 30 min at average concentrations varying from 8.0 to 19.3 mg.m-3 (mean = 11.5 mg.m-3). Twenty-five to 39.7% (mean = 34.6%) of inhaled particles had a diameter less than 10 mu (diameter allowing deposition in the trachea and lower respiratory tract). At the end of each period of exposure, FEV1 was assessed. After recovery, the second PC20 was obtained. Serial measurements of FEV1 were carried out every hour for up to 6 h after the end of exposure. At that time, PC20 was reassessed. Only one subject showed an acute bronchoconstriction immediately after exposure to sawdust (maximum fall of 14% in FEV1) with complete recovery 10 min later. Overall, inhalation of sawdust did not modify PC20 by comparing the mean result of the first test with the second and the third assessments. Also, the mean changes in PC20 at each interval after exposure to sawdust were not significantly different from the variations in PC20 on the sham day.(ABSTRACT TRUNCATED AT 250 WORDS)     

Theophylline has a dose-related effect on the airway response to inhaled histamine and methacholine in asthmatics

To study whether theophylline inhibits airway hyperresponsiveness in a dose-dependent fashion, we performed inhalation challenges with histamine and methacholine in 9 asthmatic patients. On 4 separate days, 3 consecutive histamine or methacholine tests were carried out, each of them 20 min after saline (placebo) and after 100, 100, and 200 mg intravenous theophylline ethylenediamine given in a cumulative fashion. Airway responsiveness was expressed as the provocative dosage of histamine or methacholine necessary to increase specific airway resistance by 100% (PD100SRaw). After placebo PD100SRaw for histamine showed a small but significant (p less than 0.01) increase not observed after methacholine. Theophylline markedly attenuated airway reactivity in a dose-dependent manner. At a mean (SD) serum concentration of 6.14 (0.30) mg/L, theophylline increased geometric mean PD100SRaw for histamine from 2.76 to 6.07 units (p less than 0.01) and for methacholine from 1.52 to 2.60 units (p less than 0.05). At a mean (SD) serum concentration of 12.9 (0.70) mg/L, theophylline increased geometric mean PD100SRaw for histamine from 2.70 to 17.1 units (p less than 0.01) and for methacholine from 1.28 to 4.98 units (p less than 0.01). Thus, there was a protective effect of theophylline on histamine and methacholine responsiveness in patients with bronchial asthma at "subtherapeutic" serum theophylline concentrations with increasing efficacy at higher serum theophylline concentrations. These observations may have therapeutic implications in the treatment of patients with mild asthma.     

Partitioning of pulmonary responses to inhaled methacholine in subjects with asymptomatic asthma.

To partition the central and peripheral airway resistance, a catheter-tip micromanometer sensing lateral pressure of the airway was wedged into the right lower lobe of a bronchus with a 3 mm inner diameter in 10 patients with asymptomatic asthma. We simultaneously measured mouth flow, transpulmonary pressure (PL) and intra-airway lateral pressure during tidal breathing. Total pulmonary resistance (RL) was calculated from PL and mouth flow, and central airway resistance (RC) was calculated from intra-airway lateral pressure and mouth flow. Peripheral airway resistance (Rp) was obtained by subtraction of RC from RL. Therefore, our measurement of Rp included lung tissue resistance. The technique permitted identification of the site of changes in airway resistance. The baseline values of resistances were 2.3 +/- 0.2 cm H2O/L/s in RL, 1.5 +/- 0.1 cm H2O/L/s in RC, and 0.8 +/- 0.1 cm H2O/L/s in Rp, respectively. To determine the site of airway hyperresponsiveness, dose-response curves of central, peripheral, and total airways to inhaled methacholine were separately constructed. Bronchial responsiveness was evaluated by a log methacholine unit requiring a 35% decrease (PC35) and a 50% decrease (PC50) in pulmonary conductance (a reciprocal of RL). We calculated the increase of resistances in total (delta RL), central (delta RC), and peripheral (delta Rp) airways from the baseline values at either PC35 or PC50.(ABSTRACT TRUNCATED AT 250 WORDS)     

Asthmatic airways have a disproportionate hyperresponsiveness to LTE4, as compared with normal airways, but not to LTC4, LTD4, methacholine, and histamine

Airways responsiveness to leukotriene (LT) C4, LTD4, LTE4, histamine, and methacholine have been studied in eight asthmatic and six normal subjects. Airways responsiveness to each bronchoconstrictor agonist was assessed by constructing cumulative dose-response curves, and the dose that produced a 35% decrease in specific airways conductance (PD35) was obtained by linear interpolation. Airways of subjects with asthma were approximately 14-, 15-, 6-, 9-, and 219-fold more responsive to histamine, methacholine, LTC4, LTD4, and LTE4, respectively, than were normal subjects. Thus, there was a substantially augmented level of hyperresponsiveness to LTE4 in bronchial asthma, which was not observed for the other bronchoconstrictor agents, when compared to normal subjects. In contrast to LTC4 and LTD4, as histamine and methacholine responsiveness increase, the dose ratio of histamine to LTE4 (PD35 histamine/PD35 LTE4) and the dose ratio of methacholine to LTE4 also tended to increase. This suggests that as the nonspecific airways responsiveness increases, the relative potency of LTE4 also increases, whereas potency of LTC4 and LTD4 decrease. These results suggest that the mechanism of the bronchoconstriction induced by LTE4 may be distinct from that produced by LTC4 or LTD4 in subjects with asthma. This may reflect leukotriene subtype receptor heterogeneity in asthmatic airways.     

Theophylline does not increase ventilatory responses to hypercapnia or hypoxia.

Theophylline is commonly believed to stimulate central respiratory centers. We studied the effect of oral theophylline therapy on ventilatory responses to hypercapnia and hypoxia during a double-blind placebo-controlled trial with a slow release oral theophylline preparation. We measured hypercapnic and hypoxic ventilatory responses using rebreathing techniques in 15 subjects (21 to 41 yr of age, with normal lung function) on three occasions: baseline, after 4 days of Drug 1, and after 4 days of Drug 2. For subjects receiving theophylline, the mean serum theophylline level was 11.3 + 1.3 (SE) micrograms/ml (range, 5.3 to 22.1). Unpleasant side effects were reported by 11 of the 15 subjects (nausea, jitteriness, and agitation) while receiving theophylline but not while receiving placebo. The mean hypercapnic ventilatory response with placebo was 4.3 +/- 0.9 L/min/mm Hg PACO2 and with theophylline it was 4.5 +/- 0.7 L/min/%SaO2 and with theophylline it was -2.7 +/- 0.4 L/min/%SaO2. Hypoxic responses for each subject were measured at similar PvCO2. There were no significant changes in ventilatory responses with theophylline. We conclude that theophylline use, at a dose sufficient to cause side effects, does not affect chemoreceptor responsiveness.     

Adenosine receptor subtypes in airways responses of sensitized guinea-pigs to inhaled ovalbumin

Endogenous adenosine is released in asthmatic patients’ lungs by inhaled allergen, however, its exact role in asthmatic responses or the receptors mediating these responses has not been determined. Our hypothesis was that adenosine released during allergen challenge contributes to the airways responses to inhaled allergen. The effects of selective antagonists of the four adenosine receptor subtypes were investigated on the airways responses of sensitized guinea-pigs to inhaled ovalbumin to ascertain the role of adenosine in these allergen responses, and compared with a corticosteroid, dexamethasone.Early (EAR) and late asthmatic responses (LAR) to inhaled ovalbumin (10 μg/ml) of sensitized, conscious guinea-pigs were recorded by whole body plethysmography following administration of selective adenosine receptor antagonists. Airway reactivity to inhaled histamine (1 mM) and inflammatory cell influx in bronchoalveolar lavage fluid were also determined 24 h after ovalbumin challenge.ZM241385 (A_2A receptor antagonist) did not affect these responses, whereas DPCPX (A₁ receptor antagonist) exerted a small inhibition only of the LAR. MRS1706 (A_2B receptor antagonist) inhibited the airways hyperreactivity and cellular influx and enhanced the EAR. MRS1220 (A₃ receptor antagonist) inhibited the airways hyperreactivity and cellular influx without affecting EAR and LAR. Dexamethasone inhibited the ovalbumin-induced late asthmatic responses, airways hyperreactivity and cellular influx.The blockade of airway hyperreactivity and inflammatory cell influx by A_2B and A₃ receptor antagonists suggests that endogenous adenosine is released by inhaled allergen and these responses are mediated via A_2B and A₃ receptors in guinea-pigs. The adenosine released by allergen inhalation does not, however, appear to be involved in the EAR, but it may contribute to the LAR via A₁ receptors.     

Gold does not alter the arthritic,humoral, or cellular responses in rats with type ii collagen-i nduced arthritis

We assessed the effects of administration of gold sodium thiomalate on the clinical and immunologic manifestations of type II collagen-i nduced arthritis in rats. Injections of varying doses of gold did not alter these parameters significantly. Thus, there was no evidence in this animal model that gold possesses either antiinflammatory or immunosuppressive properties.     

Naloxone does not alter response to hypercapnia or resistive loading in chronic obstructive pulmonary disease

To assess the role of endogenous opioid peptides in ventilatory control in patients with chronic obstructive lung disease, we measured the ventilatory and mouth occlusion pressure responses to hypercapnia and the compensatory response to an inspiratory resistive load in 11 male patients with COPD before and after intravenous administration of naloxone or placebo on 2 separate days. There were no statistically significant differences between naloxone and placebo administration in any index of ventilatory response to CO2 or resistive loading. When an inspiratory resistive load was added during CO2 rebreathing, minute ventilation at PETCO2 = 50 mm Hg in all 11 patients decreased significantly (p less than 0.05) with placebo and naloxone. In response to the inspiratory resistive load, in eight of the 11 patients mouth occlusion pressure (P0.1) did not increase; these eight subjects were classified as noncompensators. Naloxone did not affect the P0.1 response to inspiratory resistive loading, either in the group as a whole or in the subgroup of eight patients classified as noncompensators. Our study was unable to demonstrate that increased activity of endogenous opioid peptides suppresses the ventilatory response to CO2 or resistive loading in patients with chronic obstructive lung disease.     

General anesthesia does not alter the viscoelastic or transport properties of human respiratory mucus

Observations that mucus transport rates (MTR) are depressed in anesthetized animals and humans have led to speculation that general anesthesia depresses ciliary activity or adversely alters the physical properties of the respiratory mucus (RM). We investigated the possibility that anesthesia changes the physical properties of RM in such a way as to depress ciliary transport. We collected 33 samples of RM from the endotracheal tubes (ETTs) of 25 people aged 1 to 79 years undergoing elective surgery who had no clinical evidence of lung disease. We measured the rigidity, viscoelasticity, spinnability, and the percentage of solid composition of these specimens as well as the transport of the collected RM across the mucus-depleted frog palate. These physical properties were not significantly different from RM collected from awake volunteers using the bronchoscopy brush collection technique. Differences in spinnability, transportability, and solid content of paired mucus samples from the inside and outside of the ETTs are suggestive of altered RM hydration, but this requires further study. The decrease in MTR during general anesthesia is probably due to mechanisms other than alterations in the physical properties of mucus.     

Sodium cromoglycate-induced changes in the dose-response curve of inhaled methacholine and histamine in asthmatic children.

The effect of inhalation of 2 per cent solution of sodium cromoglycate compared to that of saline on the bronchial response to methacholine and histamine was studied in 30 asthmatic children. Seven of 17 children challenged with methacholine showed decreased sensitivity after pretreatment with sodium cromoglycate. In 4 of 13 children, sodium cromoglycate attenuated the response to inhaled histamine. We conclude that in some asthmatic children, sodium cromoglycate provides significant protection against these nonallergenic challenges. This may have some therapeutic implications in the management of these patients. Our findings raise the possibility that sodium cromoglycate might have an action on cholinergic or irritant receptor sites in addition to inhibition of mast cell degranulation.     

Bronchoconstriction due to exercise combined with cold air inhalation does not generally influence bronchial responsiveness to inhaled histamine in asthmatic subjects

We investigated immediate and late changes in airway responsiveness to histamine, after bronchoconstriction due to exercise combined with inhalation of cold air, in ten asthmatic subjects who came on six days. On the first visit, the provocation concentration producing 20% fall in FEV1 (PC20) histamine was obtained. After functional recovery, each subject walked on a treadmill whilst breathing dry, cold air. This resulted in an immediate fall greater than 15% (mean +/- SD = 31.9 +/- 11.0%) in forced expiratory volume in one second (FEV1). Following recovery, PC20 was measured again. FEV1 was then monitored for up to 6-8 h. PC20 was measured then and on the two following days at the same time of the day. Subjects were studied on three control days using the same design except that a resting period replaced the exercise with cold air. The mean changes in PC20 at each interval after exercise combined with cold air were not statistically significant. Physiologically significant changes were obtained in only two subjects, reaching a maximum 8 h after the manoeuvre. In these subjects, changes in PC20 were reproducible during a second series of visits. It is concluded that bronchial responsiveness to histamine is not generally influenced by the bronchoconstriction due to exercise combined with cold air.     

Effects of clonidine on bronchial responses to histamine in normal and asthmatic subjects

Our aim was to examine the effects of clonidine (C), an agonist of central and peripheral alpha-2 adrenoceptors, on bronchomotor responsiveness to histamine (H). In a double-blind study, we compared on two different days the effects of pretreatment with placebo (P) and with 200 micrograms or 150 micrograms of C given orally, in ten normal (NS) and eight asymptomatic asthmatic subjects (AS) respectively, the response to inhalation of serially increasing doses of H. On each day, five doubling doses of H (first dose = 3.5 and 1.1 mumol in NS and AS, respectively) were administered every 5 min; forced expiratory volume in one second (FEV1) was measured after each dose. The dose-response curves were compared by an analysis of variance. Clonidine caused hypotension with bradycardia in all subjects. Baseline values and pre-challenge values of FEV1 after P and C were identical on the two study days. Compared to P, C did not modify the response to H in NS but significantly increased it in AS (p less than 0.01). Our results suggest that the neural control of the airways differs in AS compared to NS and could be explained either by a decrease in sympathetic inhibitory activity or a greater responsiveness of the airways to parasympathetic stimulation and/or a higher parasympathetic tone in AS.     

A comparison of three measures of the response to inhaled methacholine

In studies of asthma prevalence bronchial responsiveness has usually been measured as the provocative dose of bronchoconstrictor causing a 20% fall in FEV1 (PD20FEV1). This is relatively insensitive and only 10-20% of subjects in a general population sample will show such a response. Attempts to increase sensitivity, such as the use of the provocative dose causing a 10% fall in FEV1 (PD10FEV1), have not demonstrated any overall advantage, due to poorer repeatability. It has been suggested that measurement of bronchial reactivity using flow at low lung volumes measured from a partial flow volume curve is a more sensitive index of bronchoconstriction than PD20FEV1. If equally repeatable, it would have advantages in epidemiological practice. In 20 subjects with asthma, we compared the sensitivity and repeatability of PD10FEV1, PD20FEV1, and the provocative dose causing a 40% fall in flow at 30% of vital capacity (PD40V30P) following methacholine challenge. PD40V30P was more sensitive than both PD20FEV1 and PD10FEV1 by 1.48 and 0.35 doubling doses (DD) of methacholine, respectively. PD20FEV1 and PD40V30P showed equal repeatability, the 95% range for a single estimate of both being 2.02 DD. PD10FEV1 was less repeatable, with a 95% range of 2.35 DD. Values for the intraclass correlation co-efficient, which measures the ability of a test to discriminate between subjects, were 0.63, 0.79 and 0.69 for PD10FEV1, PD20FEV1, and PD40V30P, respectively. The increased sensitivity and comparable repeatability of measurement of bronchial reactivity for PD40V30P suggest that this method may be useful for studies of asthma prevalence.     

Central infusion of L-arginine or superoxide dismutase does not alter arterial pressure in SHR.

Cardiovascular responses to L-arginine and nitric oxide (NO) are augmented in the rostral ventrolateral medulla (RVLM) of spontaneously hypertensive rats (SHR), and the intravenous injection of superoxide dismutase (SOD) mimetic decreases the arterial pressure in these rats. In the present study, we examined whether the chronic central infusion of L-arginine or an SOD mimetic would reduce the blood pressure of SHR and alter responses to an NOS inhibitor or an NO donor in the RVLM. For this purpose, we administered L-arginine (SHR-Arg: 13.2 micromol/day, n=6), a stable membrane-permeable SOD mimetic, 4-hydroxy-2, 2,6,6-tetramethyl piperidine-1-oxyl (tempol) (SHR-Temp: 13.2 micromol/day, n=6), or vehicle (SHR-C: n=6) into the lateral ventricle of 12-week-old SHR for 2 weeks. When the rats reached 14 weeks of age, N(G)-nitro-L-arginine methyl ester (L-NAME: 10 nmol/50 nl) or NOC 18 (NO donor: 10 nmol/50 nl) was microinjected into the unilateral RVLM. Blood pressure did not decrease in any of the treatment groups (SHR-Arg: 209+/-4 mmHg, SHR-Temp: 210+/-6 mmHg, SHR-C: 197+/-6 mmHg). The microinjection of L-NAME into the RVLM induced a significant increase in the mean arterial pressure (MAP) (SHR-Arg: 10-4 mmHg, SHR-Temp: 12+/-4 mmHg, SHR-C: 11+/-3 mmHg), and the increases in MAP did not differ among the groups. The micro-injection of NOC 18 reduced MAP (SHR-Arg: -12+/-2 mmHg, SHR-Temp: -15+/-3 mmHg, SHR-C: -13+/-3 mmHg), and the depressor responses were comparable among groups. These results do not support the hypothesis that chronic L-arginine deficiency or the enhanced degeneration of NO by superoxide radicals in the central nervous system contributes to the maintenance of arterial pressure in SHR.     

Hypophysectomy does not alter the effects of somatostatin or growth hormone on canine splanchnic biogenic amine release

We have demonstrated previously that growth hormone (GH) and somatostatin (somatotropin release inhibitory factor, SRIF) exert comparable effects on the release of splanchnic biogenic amines. The purpose of the present investigation was to study further the response of the two hormones and see whether the similarity persists in dogs completely deprived of endogenous GH. Experiments were conducted in seven hypophysectomized dogs fitted with an indwelling portal catheter. Two to 4 weeks after surgery the responsiveness of their catecholaminergic neurons was tested by an injection of human beta-endorphin (20 micrograms/kg); it caused a rise in portal catecholamine levels equivalent to that seen in intact dogs. Then the effect of a spike concentration of SRIF or GH on hepatic portal and peripheral levels of free serotonin and catecholamines was studied, all by radioenzymatic methods. The intravenous injection of ovine GH (100 micrograms/kg) or equimolar amounts of SRIF (7.5 micrograms/kg) produced in the hepatic portal circulation a transient but statistically significant rise of serotonin and a concomitant reduction in the concentration of dopamine, norepinephrine, and epinephrine. No changes were found in the peripheral circulation. The response patterns to SRIF or GH were virtually identical, which is in keeping with our other data, suggesting that the effect of GH on splanchnic biogenic amine secretion is SRIF-dependent and mediated by SRIF-containing neurons.(ABSTRACT TRUNCATED AT 250 WORDS)