Endogenous opiates and the control of breathing in normal subjects and patients with chronic airflow obstruction

To investigate the role of endorphins in central respiratory control, the effect of naloxone, a specific opiate antagonist, on resting ventilation and ventilatory control was investigated in a randomised double-blind, placebo-controlled study of normal subjects and patients with chronic airways obstruction and mild hypercapnia due to longstanding chronic bronchitis. In 13 normal subjects the ventilatory response to hypercapnia increased after an intravenous injection of naloxone (0.1 mg/kg), ventilation (VE) at a PCO2 of 8.5 kPa increasing from 55.6 +/- SEM 6.2 to 75.9 +/- 8.21 min-1 (p less than 0.001) and the delta VE/delta PCO2 slope increasing from 28.6 +/- 4.4 to 34.2 +/- 4.21 min-1 kPa-1 (p less than 0.05). There was no significant change after placebo (saline) injection. Naloxone had no effect on resting ventilation or on the ventilatory response to hypoxia in normal subjects. In all six patients naloxone significantly (p less than 0.02) increased mouth occlusion pressure (P 0.1) responses to hypercapnia. Although there was no change in resting respiratory frequency or tidal volume patients showed a significant (p less than 0.01) decrease in inspiratory timing (Ti/Ttot) and increase in mean inspiratory flow (VT/Ti) after naloxone. These results indicate that endorphins have a modulatory role in the central respiratory response to hypercapnia in both normal subjects and patients with airways obstruction. In addition, they have an inhibitory effect on the control of tidal breathing in patients with chronic bronchitis.

Hyperventilation-induced asthma: evidence for two mechanisms

The mechanism by which airway cooling induces airflow obstruction in asthmatic subjects has not yet been established. Using a pair of isocapnic hyperventilation challenges, with a 40-minute interval, we looked for the presence of a refractory period in 19 asthmatic patients (aged 9-18 years). The subjects fell into two groups. The eight in the "non-refractory" group showed less than a 25% reduction in response to the second challenge, but the 11 in the "refractory" group showed at least a 35% reduction. Twelve subjects also performed a hyperventilation challenge after cholinergic blockade with inhaled ipratropium bromide. In five, in whom no refractoriness after hyperventilation was seen, there was a significant protection from cholinergic blockade (p less than 0.05). In these a vagal (cholinergic) reflex seems likely. The remaining seven, who had a refractory period, received no significant protection from cholinergic blockade and therefore no evidence for the presence of any cholinergic mechanism. We conclude that two mechanisms are responsible for hyperventilation-induced asthma, one of which is a vagal reflex while mediator release may be the other.

Plasma histamine and catecholamines in stable asthmatic subjects

1. Venous plasma histamine and catecholamines were measured in stable asthmatic subjects by a recently developed specific and sensitive radioenzymatic assay. 2. Plasma histamine concentrations were significantly elevated in both extrinsic and intrinsic asthmatic subjects compared with both normal controls and patients with chronic obstructive airways disease. There was no correlation between histamine concentration and severity of airways obstruction, however. 3. Elevated plasma histamine concentrations at rest may indicate increased release of mediators from 'leaky' mast cells in asthma. 4. Plasma catecholamine concentrations in asthmatic subjects did not differ from normal and there was no correlation with severity of bronchoconstriction or with plasma histamine concentration.

Circadian variation in adrenergic responses in asthmatic subjects

1. To determine whether circadian variations in adrenergic responsiveness might underlie nocturnal wheezing in asthma, we measured cardiovascular, airway and plasma adenosine 3':5'-cyclic monophosphate (cyclic AMP) responses to stepwise infusions of L-adrenaline (0.01, 0.03 and 0.075 microgram min-1 kg-1) at 4 h intervals over 24 h in five extrinsic asthmatic men. 2. Peak expiratory flow, blood pressure, heart rate and plasma cyclic AMP showed a significant circadian variation with peak values at 16.00 hours and trough values at 04.00 hours. 3. The beta 2-adrenoceptor-mediated increases in peak flow and cyclic AMP were similar at all times, but adrenergic responsiveness (measured by response/log dose of infused adrenaline) was greater at 04.00 hours than at 16.00 hours because of the lower baseline values at night. 4. Blood pressure and heart rate responses to adrenaline infusions did not significantly differ over 24 h. 5. Airway responses to inhaled adrenaline were studied on the second day; the mean peak flow after adrenaline was similar at 16.00 hours to that at 04.00 hours and since the pretreatment values were lower at 04.00 hours, the magnitude of response to inhaled adrenaline was greater at night. 6. We conclude that there is no significant circadian change in adrenergic responses in asthma and that adrenoreceptor dysfunction is not important in the pathogenesis of nocturnal asthma.

Single-dose slow-release aminophylline at night prevents nocturnal asthma

Twelve asthmatic patients with nocturnal wheezing were given a single nocturnal oral dose of slow-release aminophylline or matched placebo in a double-blind crossover trial. A dose of slow-release aminophylline (mean 683 mg; 10.4 mg/kg) gave a therapeutic plasma-theophylline concentration 10 h later (mean 10.9 mg/l). This was not associated with any adverse effects. Mean peak expiratory flow on waking was significantly greater with aminophylline (332 +/- 31 l/min) than placebo (283 +/- 32 l/min), whereas evening values did not differ. There was a significant difference between morning and evening peak flow on placebo (mean 22%) but not on aminophylline (5%), indicating abolition of the morning fall in peak flow. This was not at the expense of response to beta-agonists, since the response to inhaled salbutamol was the same for both treatments. The use of extra metered doses of inhaled beta-agonist during the night was significantly less with aminophylline, and there was a subjective improvement in nocturnal symptoms in all patients. Slow-release aminophylline in adequate dosage appears to be the most effective treatment yet demonstrated for nocturnal asthma.

In vivo identification and distribution of alpha- and beta-adrenoceptors in rat heart and lung

Uptake of 3H-prazosin (3H-PZ), a potent alpha-adrenoceptor antagonist, and 3h-dihydroalprenolol (3H-DHA), a potent beta-antagonist, was measured in rat heart and lung after intravenous injection. 3H-PZ binding was inhibited in a dose-dependent manner by phentolamine with maximum displacement at 5 mg/kg which represented 50-70% of the total binding. 3H-DHA was inhibited by increasing doses of l-propranolol with maximum displacement at 1 mg/kg (30-70% of total binding), whereas d-propranolol was approximately 100 times less potent, confirming stereospecificity of binding. These radioligands appeared to label adrenoceptors in vivo. The distribution of both radioligands in heart, lung and blood vessels was investigated.

Composition of cereal germ preparations

Germ from wheat, rye, triticale, barley and oat was prepared by passing the grain through an Entoleter impact mill. The content of a number of important nutrients in the germ preparations was determined in order to make a preliminary evaluation of the potential use of these preparations as food ingredients. alpha-Tocopherol, polyunsaturated lipids, protein, threonine, methionine, lysine, raffinose, sucrose, thiamin and riboflavin were chosen since these are the components regarded as most important in commercial wheat germ. All the germ preparations had compositions essentially similar to published values for commercial wheat germ derived from flour milling. The germ lipids of rye and triticale had a very high content of linolenic acid which could lead to problems of oxidative rancidity. Otherwise, the germ preparations appear suitable as an alternative to commercial mill gem for food ingredient applications.

Prazosin, an alpha 1-adrenoceptor antagonist, partially inhibits exercise-induced asthma

The effect of prazosin, a potent and specific alpha 1-adrenoceptor antagonist given by inhalation (total nebulized 2 mg) was compared with placebo in a double-blind randomized study of 10 atopic asthmatic children. Prazosin significantly (p less than 0.01) reduced the severity of post-exercise bronchoconstriction (maximum fall in peak expiratory flow after exercise 21.4% +/- SEM 6.3% after prazosin compared with 42.5% +/- 7.3% after placebo). This protective action of prazosin suggests that activation of alpha 1-adrenoceptor may be involved in the pathogenesis of exercise-induced asthma either by facilitation of mast-cell mediator release or by direct contraction of bronchial smooth muscle. Prazosin did not significantly change resting bronchomotor tone or histamine-induced bronchoconstriction, suggesting no effect on bronchial smooth muscle contractility.

Prostacyclin binding to guinea pig pulmonary receptors

[3H] Prostacyclin bound to membranes of guinea pig lung. Specific binding was saturable, and the results revealed two receptor classes (Kd =16 nM and 258 nM). The binding capacity of the high affinity site was 105 fmol [3H]prostacyclin per mg of membrane protein, and that of the low affinity site was 1257 fmol per mg membrane protein. A comparison of selected prostaglandins as inhibitors of [3H] prostacyclin binding revealed some of the structural requriements of the ligand for occupation of the high affinity receptor.

A calcium antagonist, nifedipine, modifies exercise-induced asthma

In eight extrinsic asthmatic subjects (age range 16-38 years) there was a significant reduction (p less than 0.01) in the severity of bronchoconstriction after a treadmill exercise test performed 30 minutes after nifedipine 20 mg sublingually. The maximum fall in peak expiratory flow after exercise was 36.0 +/- SEM 5.3% compared with a maximum fall of 56.5 +/- 4.1% after matched placebo capsules when given in double-blind randomised manner on separate days. There was no significant resting bronchodilation or change in blood pressure or heart rate after nifedipine. there was a significant rise in venous plasma histamine during exercise with placebo (6.1 +/- 0.8 to 13.5 +/- 3.5 nmol/l, p less than 0.01) but no significant increase with nifedipine (4.6 +/- 0.6 to 4.7 +/- 0.6 nmol/l) suggesting that nifedipine inhibits the release of mast cell mediators. The dose of inhaled histamine which provoked a 20% fall in peak expiratory flow was also significantly higher (p less than 0.05) with nifedipine (1.5 +/- 0.31 mg/ml) compared with placebo (2.7 +/- 0.63 mg/ml), indicating that there is a small inhibitory effect on bronchial smooth muscle contractility. Nifedipine is a potent antagonist of calcium ion influx in smooth muscle and secretory cells, and these studies suggest that it may inhibit release of mast cell mediators and reduce bronchial smooth muscle contractility in asthma.

Venous plasma histamine in exercise- and hyperventilation-induced asthma in man

1. Venous plasma histamine was measured by a specific and sensitive radioenzymatic assay in seven male extrinsic asthmatic and six age-matched non-atopic non-asthmatic male subjects during exercise and voluntary isocapnic hyperventilation. 2. There was no change in peak expiratory flow in normal subjects with exercise or hyperventilation, but asthmatic subjects showed a 29.4 +/- SEM 5.8% fall after exercise and a 29.0 +/- 5.4% fall after matched hyperventilation. 3. Plasma histamine was significantly higher (P less than 0.05) in asthmatic (6.2 +/- 0.95 nmol/l) than that in normal subjects (3.4 +/- 0.61 mol/l) and showed a significant (P less than 0.01) rise (to 14.4 +/- 1.83 nmol/l) during exercise in asthmatic, but not in normal subjects. This suggests that discharge of mast-cell mediators may occur during exercise in asthmatic subjects who develop exercise-induced asthma. 4. With hyperventilation there was no change in plasma histamine in either asthmatic or normal subjects, but this does not exclude the possibility that mediators may be released locally in the airways.

Circulating catecholamines in exercise and hyperventilation induced asthma

Plasma noradrenaline, adrenaline, and cyclic 3'5' AMP (cAMP) were measured in seven asthmatic patients with known exercise-induced bronchospasm and six matched non-atopic control subjects during a standard treadmill exercise test and then during matched isocapnic hyperventilation. Normal subjects showed a 5.5 fold rise in noradrenaline and a 3.2 fold rise in adrenaline during exercise compared with a 2.1 fold rise in noradrenaline and no significant rise in adrenaline in asthmatics who all developed bronchoconstriction after exercise (mean fall in peak flow rate 28.4 +/- 5.8%). Plasma cAMP rose 1.4 fold in controls but showed no significant rise in asthmatics. This reduced sympatho-adrenal response to exercise in asthmatics is difficult to explain. The failure of circulating catecholamines to rise and stimulate beta adrenoceptors on the mast cell may facilitate the release of bronchoconstrictor mediators. Matched hyperventilation produced bronchospasm in asthmatics (mean fall in peak flow rate 29.0 +/- 4.4%) but no change in catecholamines in either group suggesting that circulating catecholamines have no direct role in exercise-induced bronchospasm but may play a permissive role via the mast cell.

Partial flow-volume curves to measure bronchodilator dos-response curves in normal humans

We examined the use of partial expiratory flow-volume (PEFV) curves to obtain dose-response curves to an inhaled beta 2-adrenoceptor agonist (salbutamol) in eight normal subjects. Maximum expiratory flow at low lung volumes increased on both PEFV and full expiratory flow-volume curves, but the increase was always considerably greater on PEFV (28.4%) than on full (14.5%) curves. The percent increase in flow on the PEFV curve was not significantly influenced by the preceding volume history being 90-120 s of tidal breathing, forced expiration to residual volume, or breath holding after a full inflation. These results suggest that normal tone during tidal breathing is temporarily reduced but not abolished by a full inflation, and once basal tone has been restored it is not enhanced by a full expiration. In seven of the eight subjects a satisfactory cumulative dose-response curve to inhaled salbutamol was obtained with a plateau value of maximum flow at a dose of 110 microgram. The relatively good reproducibility of PEFV curves and the considerable bronchodilator signal obtained (29-70% increase in flow above base line in different individuals) suggest that such dose-response curves may be useful in studying normal bronchial pharmacology in vivo.

Inhaled prazosin in asthma

Prazosin, a potent and selective alpha-adrenergic antagonist, was given by inhalation to nine asthmatic subjects aged 25-48 years (six with positive skin tests). Prazosin 0.5 mg, salbutamol 1 mg, or placebo were given by nebuliser in randomised double-blind fashion on separate days. Although all subjects showed a significant increase in FEV1, vital capacity, and maximum expiratory flow at 70% of total lung capacity after salbutamol, there was no significant difference between prazosin and placebo. This suggests that alpha-adrenergic receptors are not important in the control of bronchial tone in asthma. The weak bronchodilatation ascribed to alpha-antagonists in previous studies could be explained by other pharmacological actions of the drugs used.

Preoperative cimetidine--effects on gastric fluid

A double blind study of 44 patients (24 placebo, 20 cimetidine) was undertaken to determine tha effect of cimetidine on the pH and volume of gastric fluid during anaesthesia. The pH was significantly higher on cimetidine-treated patients than placebo-treated patients at 0, 15, 30 and 45 minutes following intubation. At induction of anaesthesia, mean pH on cimetidine was 4.5 and on placebo mean H was 2.0. Approximately 70% of patients on cimetidine and 20% on placebo recorded a pH above 2.5 during anaesthesia. The reason for a pH recording of less than 2.5 in seven patients on cimetidine could not be ascertained. Mean volume of gastric aspirate was slightly lower in the cimetidine group at 0, 15, 30 and 45 minutes, but the differences were not significant.

Anaesthetic complications requiring intensive care. A five year review

In a five-year period 110 patients were admitted to the intensive therapy unit (ITU) as a result of 'a complication related to anaesthesia'. The nature of the complication and its outcome are analysed. The most common reasons for admission were cardiopulmonary arrest (32), failure to reverse after muscle relaxants (25), airway problems, and various drug reactions. Twelve deaths occurred in the 110 cases studied.

Activation of guinea pig pulmonary adenylate cyclase by prostacyclin

Prostacyclin activates adenylate cyclase of guinea pig lung homogenates. The concentration for half-maximum activation was 20 nM. Kinetic analysis of the increase in enzyme activity suggested a non-cooperative, bimolecular interaction between prostacyclin and a single receptor population. Comparison of the activity of prostacyclin with that of other prostaglandins revealed a rank order of potency: prostacyclin > prostaglandin E1 > prostaglandin E2 > prostaglandin F1 alpha. 6-Oxo-prostaglandin F1 alpha, the stable hydrolysis product of prostacyclin, produced no increase in adenylate cyclase activity. Lungs were dissected before homogenisation, and prostacyclin-sensitive adenylate cyclase was identified at high concentrations in peripheral lung tissue containing small airways, blood vessels and parenchyma. The precise cellular location of these receptors remains obscure, but the probability that they are in the pulmonary vascular bed rather than airway smooth muscle is discussed.

Human lung adrenoreceptors studied by radioligand binding

1. Direct radioligand-binding techniques have been used to characterize and quantify adrenoreceptors in human peripheral lung tissue removed at thoracotomy from ten patients, nine of whom had evidence of obstructive airways disease. 2. [3H]Dihydroalprenolol was used to characterize beta-adrenoreceptor sites and [3H]prazosin to identify alpha-adrenoreceptor sites. Binding of both ligands showed saturability, high affinity, rapid kinetics, reversibility and stereospecificity. The rank order of agonists and antagonists inhibiting specific binding correlated well with known physiological potencies. Specificity of [3H]dihydroalprenolol binding suggested that the population of lung beta-adrenoreceptors is predominantly of the beta 2 subtype.