Plasma cyclic nucleotide levels in juvenile-onset diabetes.

In patients with juvenile-onset diabetes, plasma concentrations of 3',5'-adenosine cyclic monophosphate (cAMP) were significantly lower than those of norman subjects [16 +/- 4 and 24 +/- 7 pmol per milliliter (p less than 0.025), respectively] as determined in this laboratory; whereas there were essentially no differences in plasma levels of 3',5'-guanosine cyclic monophosphate (cGMP). Because cAMP inhibits cell growth and cGMP stimulates it, these findings may represent an important factor in the atherosclerotic and obliterative angiopathies of diabetic individuals. We observed that cyclic nucleotide values were the same whether or not the subjects were receiving insulin. Those given insulin plus enough glucose to maintain hyperglycemia revealed modest elevations in cyclic nucleotide levels. Thus, the ratio of cAMP to cGMP, abnormally low in juvenile-onset diabetes, is relatively independent of short-term variations in plasma levels of either glucose of insulin.     

Plasma catecholamines during exercise-induced bronchoconstriction in bronchial asthma.

Plasma levels of adrenaline and noradrenaline during and after submaximal exercise in patients with bronchial asthma were investigated. Three groups were studied comprising 10 patients with exercise-induced bronchoconstriction (EIB), 10 asthmatic patients without EIB and four normal control subjects. Plasma catecholamines were measured at rest, at the end of exercise, and five and 15 minutes after exercise. Changes in airway resistance were assessed by measuring peak expiratory flow rate. Significant differences in catecholamine levels between reacting and non-reacting patients were found. In 10 patients developing EIB adrenaline and noradrenaline levels had risen significantly by the end of exercise and remained elevated up to the fifth minute of recovery. The rise in catecholamine levels in non-reacting asthmatics was insignificant. In control subjects noradrenaline had increased significantly by the end of exercise.     

Ketotifen in atopic asthma and exercise-induced asthma.

The efficacy of ketotifen, a tricyclic benzocycloheptathiophene derivative, was assessed in an outpatient clinical trial and in a group of 12 asthmatic subjects with exercise-induced asthma. Subjects in the outpatient trial had mild asthma and consisted of two groups: a group of 24 atopic asthmatics with at least one positive skin test reaction and with an associated history of bronchial reactivity to at least one allergen; and a group of eight asthmatics with one or more positive skin prick tests but not bronchial reactivity to an allergen. Both groups took four weeks medication of ketotifen 1 mg bd and placebo in a randomised double-blind crossover study. There was no difference between ketotifen and placebo for any measurement made during the study and consequently no evidence of drug efficacy. The exercise study followed a standardised protocol and each subject took in random double-blind order, placebo, 1 mg, 2 mg, and 4 mg ketotifen two hours before exercise. There was no difference in the mean decreases in lung function from pre-exercise baseline values after three doses of ketotifen than with placebo. Drug levels suggested ketotifen was well absorbed. It would appear that if given for a period of only four weeks ketotifen had no beneficial effects in the management of mild asthma, and that a single dose before exercise does not modify exercise-induced asthma.     

Dose-response study of sodium cromoglycate in exercise-induced asthma.

Ten patients with exercise-induced asthma participated in a single-blind dose-response study comparing the protective effect of inhaled sodium cromoglycate in increasing concentrations from 2 to 40 mg/ml. Saline was used as a control. Effects were assessed from the mean maximal percentage fall in forced expiratory volume in one second (FEV1) after the patients had run on a treadmill for eight minutes. There was slight bronchodilation evident from the increase in baseline FEV1 after inhalation of sodium cromoglycate, the difference reaching statistical significance with the highest concentration (5.7%, p less than 0.05). After exercise the maximal percentage falls in FEV1 (means and SEM) after saline and after sodium cromoglycate at 2, 10, 20, and 40 mg/ml were 37.3 +/- 4.7, 17.3 +/- 4.1, 10 +/- 3.3, 7.6 +/- 2.4, and 12 +/- 2.9. Sodium cromoglycate inhibited the exercise-induced fall in FEV1 at all the concentrations used in the study (p less than 0.001) and its inhibitory effect increased from 2 to 20 mg/ml. The mean FEV1 returned to baseline values within 15 minutes at higher concentrations of sodium cromoglycate (20 and 40 mg/ml) and a small bronchodilator effect was noted at 30 minutes. The findings suggest that the protective effect of sodium cromoglycate in exercise asthma is dose related. At higher concentration the drug suppresses chemical mediator release from the lung mast cells and may also modify the bronchial reactivity to release mediators.     

Sodium cromoglycate and ipratropium bromide in exercise-induced asthma.

In thirteen patients with extrinsic asthma the effects of placebo, sodium cromoglycate, ipratropium bromide, and ipratropium bromide plus sodium cromoglycate were studied in a random double-blind fashion to assess their inhibitory action in exercise-induced asthma (EIA). Exercise testing consisted of steady state running on an inclined treadmill for up to eight minutes. In eight of the 13 patients studied the baseline ratio of expiratory flow at 50% vital capacity (VC) breathing helium-oxygen (V50He) to V50air was over 1.20 and they were called responders; the remaining five patients were called non-responders. There was a significantly lower baseline maximum mid-expiratory flow rate (MMEF) in non-responders (P less than 0.02) as compared to responders but no difference in forced expiratory volume in one second (FEV1) or forced vital capacity (FVC). Sodium cromoglycate (P less than 0.02), ipratropium bromide (P less than 0.01), and ipratropium bromide plus spdium cromoglycate (P less than 0.01) all significantly inhibited the percentage fall in FEV1 after exercise in the responders. Ipratropium bromide had no preventive action on non-responders, unlike sodium cromoglycate (P less than 0.05) and ipratropium bromide plus sodium cromoglycate (P less than 0.02). It is postulated that mediator release is an important factor in development of EIA in most extrinsic asthmatics, whereas cholinergic mechanisms are relevant only in those patients in whom the main site of airflow obstruction is in the large central airways.     

Cholinergic blockade in the prevention of exercise-induced asthma.

The contribution of vagal mechanisms to exercise-induced asthma has been studied in 10 adult asthmatic patients using the anticholinergic drug ipratropium bromide. Exercise tests were performed for eight minutes on a cycle ergometer and each individual's tests were standardised by matching oxygen uptake. Two tests were done on each of three study days, the first being without previous medication, and the second preceded by inhalation of ipratropium bromide, 0.1, or 1 mg or saline placebo given 90 minutes beforehand. The mean falls in FEV1 and PEFR after the initial tests were very similar on the three study days. The mean falls in FEV1 after the second test were 22.3%, 19.5%, and 12.5% with placebo, 0.1 mg, and 1 mg ipratropium bromide respectively. Only the higher dose was significantly better than placebo. The results were also analysed using a protection index to compare the first and second tests each day and 1 mg ipratropium bromide was significantly better than both 0.1 mg and placebo. Similar results were obtained using PEFR. Equal bronchodilatation was produced by the two doses of drug. We conclude that conventional doses of anticholinergic drugs are not effective in preventing exercise-induced asthma, while large doses may do so in the same group of subjects.     

Protective effects of repeated short sprints in exercise-induced asthma.

Many asthmatic patients demonstrate bronchial lability with a six-minute period of exercise, which is characterised by an initial bronchodilatation followed by bronchoconstriction. This early bronchodilatation response has been further analysed by investigation of the effects of repeated 30-second sprints before and after a six-minute run. It was found that these repeated short sprints did not induce bronchoconstriction, resulted in less bronchoconstriction after a subsequent six-minute run, and caused bronchodilatation if exercise-induced bronchoconstriction was present. It is postulated that this effect may be related to an increase in circulating catecholamines or altered vagal-sympathetic balance.     

Inhaled frusemide and exercise-induced bronchoconstriction in children with asthma.

BACKGROUND--Nebulised frusemide has been shown to be protective against bronchoconstricting stimuli in adult asthmatic subjects and against cold air challenge in children. Animal studies suggest that inhaled frusemide may be more effective in the young. METHODS--A double blind placebo, controlled, crossover study on the effect on exercise of pretreatment with frusemide (20 mg) from a metered dose inhaler via a large volume spacer (Volumatic) was performed in 12 asthmatic children. Exercise testing consisted of eight minutes of running on a treadmill in an environmentally controlled laboratory. RESULTS--Deterioration in lung function was less after frusemide than after the placebo exercise tests. The mean (95% CI) maximum percentage falls in forced expiratory volume in one second (FEV1) were 14.4% (7.7 to 21.0) for placebo and 5.7% (2.3 to 9.0) for frusemide. CONCLUSIONS--Inhaled frusemide via a metered dose inhaler reduces exercise-induced bronchoconstriction in children.     

Inhibition of exercise-induced asthma by different pharmacological pathways.

Exercise-induced asthma (EIA) was provoked by standardized treadmill running for 6 minutes in 15 asthmatic children. The tests were carried out after the administration of a placebo, salbutamol, sodium cromoglycate, choline theophyllinate, and atrophine methonitrate aerosol in randomized fashion on different days. The mean post-exercise percent fall in peak expiratory flow rate was 45-2, 4-1, 19-6, 18-3, and 24-9 respectively. The proportion of children having significant amelioration of their EIA compared with those taking the placebo was 100% for salbutamol, 80% for cromoglycate and theophyllinate, and 60% for atropine. Salbutamol, choline theophyllinate, and atropine were bronchodilators at rest whereas cromoglycate was not, and the ability to suppress EIA was unrelated to bronchodilator effect. Even after bronchodilatation at rest, further broncho-dilatation occurred during the exercise period.     

Effect of an inhaled antihistamine on exercise-induced asthma.

The ability of the H1 receptor antagonist clemastine to prevent exercise-induced asthma (EIA) has been studied in 10 adult asthmatic subjects. Exercise was performed for eight minutes on a cycle ergometer on two occasions on each of two days. The first test each day was without premedication and the second was preceded by inhalation of 0.05% clemastine or saline placebo given single blind in random order. Ventilatory function was assessed by serial measurements of peak expiratory flow rate (PEFR) and forced expiratory volume in one second (FEV1). All four tests for each patient were closely matched in terms of oxygen uptake and total ventilation which were monitored throughout exercise. The response to exercise after clemastine or placebo has been compared both directly and in terms of the degree of protection afforded against EIA compared with the initial test on the same day. Clemastine was significantly better than placebo for both PEFR and FEV1. All 10 subjects had less EIA after clemastine, which suggests an important role for histamine in its production. Other mechanisms may also be involved to a variable degree in different individuals.     

Multiple cyclic nucleotide phosphodiesterases in rat kidney.

Using DEAE-cellulose chromatography and Agarose gel filtration we have partially purified a low Km cyclic adenosine monophosphate (AMP) phosphodiesterase from the 100,000 X g supernatant of rat kidneys. The characteristics of this enzyme included a Km of approximately 4 muM a pH optimum of around 8.0 and a requirement for magnesium. This preparation should be suitable for investigation of possible effects of hormones, drugs and cellular constituents on the cyclic AMP pathway through any direct effects on the low Km enzyme. We have also demonstrated a nonspecific, high Km cyclic nucleotide phosphodiesterase and possibly a specific cyclic guanosine monophosphate (GMP) phosphodiesterase in the soluble fraction from rat kidneys.     

Controlled-analysis of the effects of inhaled lignocaine in exercise-induced asthma.

To determine whether anaesthesia of the intrathoracic airways would attenuate the development of exercise-induced asthma, we studied eight symptomless asthmatic patients by cycle ergometry after saline or lignocaine pretreatment while they were breathing air at 24 degrees C with 9.1 mg of H2O/l. Pulmonary mechanics were measured before and after the administration of each agent, and again five minutes after cessation of exercise. Sufficient lignocaine was administered to abolish the gag reflex and the cough response to aerosols of citric acid. Before exercise there were no significant differences for any lung function variable between the saline and lignocaine results. Equally, there were no significant differences between these agents for minute ventilation (VE) during exercise (VE lignocaine = 71.0 +/- 7.4 (SEM) l/min; VE saline 67.2 +/- 8.1 l/min;), or in the severity of the subsequent bronchospastic response (for example, the FEV1 with saline was 22.6 +/- 2.9% decrease, and with lignocaine 23.6 +/- 8.5%). Thus these results do not support the idea that there are thermally sensitive neural receptors in intrathoracic airways that play a role in the pathogenesis of exercise-induced asthma.     

Respiratory heat loss in exercise-induced asthma. Measurement and clinical application

The theoretical considerations of conditioning inspired air and the application of the respiratory heat loss (RHL) formula are discussed. An on-line method for measuring RHL is described together with the apparatus for generating frigid dry and warm humid air. Exercise-induced asthma (EIA) was studied using these methods. Thirteen asthmatic and 6 normal children and adolescents participated in the study. Each subject undertook two submaximal exercise tests consisting of 6 minutes' ergometric cycling against a fixed load. One test was done while breathing cold dry air (mean temperature -22 degrees C and 0% relative humidity) and the other while breathing warm humid air (mean temperature 36 degrees C and 100% relative humidity). All the other exercise parameters (e.g. heart rate, minute ventilation, oxygen uptake) were carefully matched between the two tests. In the cold dry air tests with a mean RHL of 1,43 kcal/min, all asthmatic subjects developed EIA with a mean fall in forced expiratory volume in the 1st second (FEV1) of 48% from baseline. In the warm humid air tests with negligible RHL (0,02 kcal/min) none of the asthmatics developed EIA (mean fall in FEV1 5%). The difference between the two tests was highly significant (P less than 0,001). Neither air condition caused bronchospasm in the normal subjects. A dose-response relationship was obtained between the degree of RHL and corresponding fall in FEV1.     

An unusual example of exercise-induced asthma

A patient with exercise-induced asthma is described in whom the post-exercise fall in F.E.V.₁ was not prevented by the inhalation of isoprenaline immediately before exercise but was almost completely prevented by subcutaneous atropine given 40 minutes before exercise. A large fall in F.E.V.₁ similar to the fall after exercise occurred after carbon dioxide-induced hyperventilation and voluntary hyperventilation performed at rest. Only a slight fall in F.E.V.₁ occurred when atropine was given before voluntary hyperventilation was performed. It is postulated that the post-exercise fall in F.E.V.₁ in this patient is due to hyperventilation reflexly causing bronchial constriction.     

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.     

Vardenafil‐induced relaxation and cyclic nucleotide levels in normal and obstructed rat urinary bladder

OBJECTIVE

To study the effects of the phosphodiesterase‐5 inhibitor, vardenafil, on contraction and cyclic nucleotide levels in isolated detrusor preparations with and without mucosa, from control rats and rats with partial urethral obstruction (PUO) and intact mucosa.

MATERIALS AND METHODS

Female Sprague‐Dawley rats were divided into groups subjected to PUO for 14 days (six), and sham‐operated control rats (12). Detrusor preparations were mounted in organ baths and effects of increasing concentrations of vardenafil (1 nm to 100 µm ) assessed on carbachol‐activated (1 µm ) preparations, and on contractions induced by transmural activation of nerves (electrical field stimulation, EFS). Levels of cGMP and cAMP were determined using radioimmunoassays.

RESULTS

Vardenafil caused concentration‐dependent relaxations of carbachol‐contracted detrusor, the mean (sd ) of which at 100 µm was 91 (4)% in control and 100% in PUO rats. The ?log 50% inhibitory concentration (IC₅₀) was 4.41 (0.08) and 4.73 (0.05) (P < 0.01), respectively. Removing the mucosa increased the relaxant effect of vardenafil at 1–10 µm (P < 0.05) although ?log IC₅₀ values were unaffected compared to the control. The cGMP levels ( pmol/mg protein) in control preparations increased from 2.5 (0.6) to 5.0 (0.8), and from 1.4 (0.2) to 7.2 (1.3) in obstructed bladders. In mucosa‐denuded preparations the cGMP content increased from 0.6 (0.1) to 1.6 (0.4) in response to vardenafil. In control rats, the levels of cAMP increased from 12.8 (2.5) to 18.9 (0.9) (P < 0.05) after vardenafil. In mucosa‐denuded preparations the cAMP levels after vardenafil increased from 16.5 (2.11) to 37.8 (3.4) (P < 0.01). In PUO bladders, the tissue content of cAMP increased from 12.6 (2.4) to 20.6 (3.4) (P < 0.01). Vardenafil concentration‐dependently inhibited nerve‐induced contractions in all groups studied. At 100 µm 19 (3)% of the control contraction remained, vs 8 (1)% for preparations from obstructed rats, and 11 (4)% in mucosa‐denuded preparations.

CONCLUSION

In normal rats, vardenafil relaxed carbachol‐ and inhibited EFS‐induced contractions of detrusor preparations with and without urothelium, and in PUO rats with urothelium. Relaxations were accompanied by increases in both cAMP and cGMP content. It is proposed that vardenafil‐induced relaxation of rat detrusor, also in obstructed and mucosa‐denuded preparations, is mediated via cAMP.     

Effects of ascorbate on leucocytes: Part I. Effects of ascorbate on neutrophil motility and intracellular cyclic nucleotide levels in vitro.

A preliminary series of experiments indicated that ascorbic acid and calcium and sodium ascorbate in the absence of serum had no stimulatory effect on neutrophil motility. However, when neutrophils were pre-incubated with ascorbate at concentrations between 5 X 10(-2)M and 1 X 10(-1)M in the presence of fresh normal autologous serum (5% final concentration) considerable stimulation of random motility and migration towards the leuco-attractants C5a and casein was observed. The serum factor required for ascorbate-mediated enhanced locomotion was heat unstable and was probably not serum albumin since no stimulation of cell migration was observed when serum was replaced with varying amounts of human serum albumin. Calcium ascorbate was the most potent stimulant of neutrophil motility. Concentrations of calcium and sodium ascorbate which increased migration promoted elevation of intracellular cyclic guanosine monophosphate (cGMP) levels, but not of adenosine monophosphate (cAMP). These same concentrations also caused increased glyclytic activity. It is suggested that the enhanced neutrophil motility mediated by ascorbic acid and calcium and sodium ascorbate in the presence of serum may be due to increased cGMP and/or glycolysis.